An efficient protocol for the synthesis of highly sensitive indole imines utilizing green chemistry: optimization of reaction conditions

Abstract

Novel and highly sensitive indole-based imines have been synthesized. Their synthesis has been compared employing a variety of protocols. Ultimately, a convenient, economical and high yielding set of conditions employing green chemistry have been designed for their synthesis.

Introduction

The Schiff bases, a subclass of imines [1,2,3] first discovered by Schiff in 1864 [1], are compounds with the general formula RHC = $\hbox {N-R}^{1}$, where $\hbox {R}^{{1}}$ may be aryl, cycloalkyl or heterocyclic groups [1, 3, 4]. Schiff bases have been found to exhibit a broad range of biological activities such as anticancer [5,6,7], antitumor [8], anti-inflammatory [9], insecticidal [10], antibacterial [11,12,13,14,15], antituberculosis [16, 17], antimicrobial [18, 19], anticonvulsant [20], antifungal [15, 21, 22], antimalarial [23] and antiviral [15, 24], (including antiHIV-1 [25]) activities. Imines, acting as ligands to furnish extensively used coordination complexes [26], have physiological and pharmacological importance [27], are being widely used for metal ion extraction [28] and heavy metal ion estimation in environmental samples [29]. Imines often play a major role in organic catalysis [30], e.g., cyclopropanation and epoxidation of alkenes [31, 32], ring-opening polymerization of lactide [33], trimethylsilyl-cyanation of aldehyde [34], enantioselective oxidation of MeSPh [35] and enantioselective epoxidation of silyl enol ethers [28].

The nucleophilic attack of an amine at the $\hbox {C}{=}\hbox {O}$ functionality is a reversible reaction and the likelihood of imine formation largely depends on the rate of $\hbox {H}_{{2}}\hbox {O}$ removal [36]. Use of azeotropic distillation [37], dehydrating agents ($\hbox {Na}_{2}\hbox {SO}_{\mathrm {4 }}$ or molecular sieves etc.) [38] and dehydrating solvents [$\hbox {Si(OMe)}_{\mathrm {4}}$ or $\hbox {CH(OMe)}_{\mathrm {3}}$, etc.] [39, 40] also facilitates $\hbox {H}_{2}\hbox {O}$ removal. A lot of catalysts such as organic acids, mineral acids, Lewis acids, natural catalysts, polymers or even dehydrating agents are used for the synthesis of imine in appreciable yield (Table 1).

Green chemistry requires cleaner and eco-friendly methods of synthesis. Replacement of toxic, costly and volatile organic solvents is of prime importance. Enhancement in reaction efficiency, selectivity, ease of product separation and purification are being achieved by solvent-free approaches [41,42,43,44,45,46,47]. Acceptable yields of imines have also been reported in $\hbox {H}_{2}\hbox {O}$, as suspension, using no acid catalyst [48] and MW-assisted solvent-free conditions. Better selectivity and easy workup showed improvement in reaction rates [49] but this methodology is limited to small-scale reactions [50]. Table 1 presents a comparison of reported Schiff-base synthesis by protocols (entries 1–34) using organic solvents/$\hbox {H}_{2}\hbox {O}$ with catalysts applying green strategies [51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80].

Table 1 Comparison of Schiff-base synthesis by different reported methods

The use of aromatic solvents under high temperature conditions poses a severe health risk. Dehydrating agents are not usually efficient enough to trap all the $\hbox {H}_{2}\hbox {O}$ produced during a reaction. Therefore, the exploration of a convenient, high yielding and environment friendly methodology for furnishing targeted indole-fused imines was pursued. The condensation of 7-formylindoles with various aromatic 1°-amines was carried out using different conditions which included:

• 1. Natural lemon juice catalyzed condensation.

• 2. Condensation by refluxing in dry solvent (EtOH/MeOH) without catalyst.

• 3. The $\hbox {H}_{2}\hbox {O}$-assisted condensation.

• 4. Catalyst- and solvent-free condensation (SFC).

Scheme 1

a benzoin, $\hbox {PhNH}_{2}$, AcOH, reflux; b $\hbox {POCl}_{{3,}}$DMF; c lemon juice (5 mL), ambient; d dry EtOH, reflux; e 180 ºC; f $\hbox {H}_{2}\hbox {O}$/$\hbox {CHCl}_{{3}}$ (15:1), reflux

The use of above protocols offered several advantages such as:

• 1. Use of economically inexpensive and harmless reaction media (e.g., $\hbox {H}_{2}\hbox {O}$/lemon juice).

• 2. Avoidance of drying agents and catalysts.

• 3. Ease of product isolation (just simple filtration from reaction medium) in all above cited approaches (except 1).

The main indole nucleus of 2a and 2b has already been recognized for its anticancer, antimicrobial and many other biological activities. These indole imines can serve as a target for exploration of the aforementioned and many other biological activities. Furthermore, the position of donor (N) atoms in indole imines 4–15 makes these substrates potent ligands for complexation/chelation. If bound with metals to furnish six-member ring, these kinds of ligands can assume an excellent inhibitory character.

Results and discussion

We adopted a modified Bischler indole synthesis [81,82,83] to produce a series of 4,6-dimethoxy-2,3-diphenyl-(1H)-indoles 2a and 4,5,6-trimethoxy-2,3-diphenyl-(1H)-indoles 2b by employing commercially available substituted $\hbox {PhNH}_{2}$ 1a–b and benzoin. The indole ring formation was verified by various spectroscopic techniques. Concrete evidence was provided by single-crystal XRD studies (Fig. 1, Table 4). Indoles 2a–b were formylated via a Vilsmeier–Haack reaction in which the chlorinating agent is the chloroiminium ion intermediate, generated from the reaction between DMF and $\hbox {POCl}_{{3}}$ [84]. 7-Fomylindoles 3a–b were condensed with a variety of $\hbox {PhNH}_{2}$ derivatives to afford novel indole imines 4–15 (Scheme 1).

The disappearance of a signal corresponding to $\hbox {H}^{{7}}$ in the aromatic region and the emergence of a new singlet at 10.41 ppm (CHO) confirm formylation. Supportive proof came from the $^{\mathrm {13}}$C-NMR, which recorded $\hbox {C}^{\mathrm {5}}$ as a doublet and $\hbox {C}^{{7}}$ as a quaternary carbon. Moreover, the aldehyde C$=$O singlet emerged at 188.2 ppm. The downfield shift of $\hbox {C}^{{7}}$ may be due to electron withdrawing (–I and –R) effects of the aldehyde functionality. The bathochromic shift in the $\lambda _{\max }$ of formylated indoles 3a and 3b (372, 358 nm) as compared to reactants 2a–b (322, 318 nm) and the appearance of C$=$O at 1606 $\hbox {cm}^{\mathrm {-1}}$ indicate the successful introduction of a carbonyl functionality. The EIMS of formylated indoles exhibited [M]$^{\mathrm {+\cdot }}$ as the base signal, no further fragmentation was observed. The XRD studies finally concluded the structure of 3a–b (Fig. 1, Table 4).

Fig. 1

ORTEP presentation of 2a (left) and 3b (right)

Table 2 Optimization of conditions for imine synthesis

Table 3 Comparison of yields of imines 4–15 using different protocols

In the beginning the conversion of reactants into products remained incomplete after changing a variety of protocols. This pointed out the reversibility of imines. We observed that the acidic nature of silica on TLC (for monitoring the progress of reaction) was misguiding the completion of reaction, converting the product (imine) back into the reactant (aldehyde) on the TLC plate. The TLC plate was neutralized by eluting with $\hbox {Et}_{{3}}\hbox {N}$ and n-hexane (2:3), prior to TLC to monitor the progress of the reaction. Similarly, the use of neutralized $\hbox {CHCl}_{{3}}$ (obtained by eluting through a thin and short column packed with $\hbox {NaHCO}_{{3}})$ for TLC showed no decomposition. With this strategy no traces of reactant were observed, showing completion of reaction.

The reversibility in the formation of imine would be due to the poor electrophilicity of C$=$O (attributed to strong $+$R effect of OMe groups of indole ring) as well as the poor nucleophilicity of anilines. Since column chromatography could not be adopted under such circumstances, therefore, attempts were made to synthesize imines with complete consumption of reactants. Four strategies gave fruitful results briefly discussed in the introduction.

Employing NaOH [85], HCl [60] and AcOH [53, 56, 57] resulted in no product formation. To avoid harsh conditions and the need to use high temperature, a reported procedure, in which lemon juice was used as a catalyst, was tried [77, 78]. The use of natural lemon juice as a catalyst has a few advantages over other catalysts, since it is an eco-friendly method, which in our case afforded better results (60–80% yield). Lemon juice may contain some organic acids and metals (which may coordinate to C$=$O to increase the electrophilicity of 7-formylindoles 3a–b) that may contribute to its better catalytic profile. The imines thus formed were separated by partitioning between $\hbox {CHCl}_{{3}}$ and $\hbox {H}_{2}\hbox {O}$. A little decomposition of imines was observed upon workup, which may be due to acidic aqueous medium. Neutralizating the reaction mixture first with 0.5M aq $\hbox {NaHCO}_{{3}}$followed by partitioning with $\hbox {CHCl}_{{3}}$ avoided the decomposition of imines; however, this did not improve the reaction yield.

To avoid acidic medium, 7-formylindoles 3a–b and $\hbox {PhNH}_{{2}}$derivatives were refluxed in dry EtOH, which afforded crystalline product in better yield (70–95%) by just washing thoroughly with dry EtOH/MeOH to remove unreactive aniline. The long reaction duration ($\ge$ 70 h) drove us to think about an alternate strategy.

The $\hbox {H}_{2}\hbox {O}$-assisted condensation proved to be detrimental for the formation of imines 4a–15a; however, the same strategy furnished better yields (77–94%) for imines 4b–15b (Table 2). The condensation of anilines with 7-formylindoles 3a–b in molten state (solvent-free condition, SFC) provided excellent yields (78–98%, Table 2). The accumulation of $\hbox {H}_{2}\hbox {O}$-droplets above the reactants near the neck of flask indicated the progress of reaction.

In order to check the effect of substituents, on indole and phenyl rings, on the yield of product the aforementioned conditions were employed for the condensation of 7-formylindoles 3a/3b with a variety of substituted aniline. The comparison of yields of the product is displayed in Table 3.

The successful condensation of 7-formylindoles 3a–b with various substituted $\hbox {PhNH}_{2}$ to afford the desired imines was verified by various spectroscopic techniques. Primarily, the transformation was supported by the disappearance of IR absorptions of HC$=$O at 1608, 1647 $\hbox {cm}^{\mathrm {-1 }}$ for 3a–b, respectively, and emergence of new signals at $1560\pm 20\,\hbox {cm}^{\mathrm {-1}}$ indicating C$=$N absorptions. The $\lambda _{\mathrm {max }}$ indicated a bathochromic shift from $355\pm 20$ (3a–b) to $370\pm 20\,\hbox {nm}$ (4–15) due to an increase in conjugation. The expected increase in $\lambda _{\mathrm {max}}$ was about 450–500 nm due to increase in conjugation of an additional aromatic ring. It indicates that the resonance of additional phenyl ring to indole nucleus would be restricted due to the presence of two phenyl groups at indolic ring, which pushes the incoming phenyl ring out of plane; hence, its contribution to the resonance is not observed in UV/Vis studies.

Fig. 2

ORTEP presentation of 10b

Table 4 Crystal data of 2a, 3b and 10b

The disappearance of a singlet of HC$=$O at 10.41/10.43 ppm of 3a and 3b, respectively, and the appearance of a singlet corresponding to HC$=$N at 9.00 ± 0.15 ppm in the $^{\mathrm {1}}$ H-NMR confirmed the imine formation. Furthermore, additional signals of aromatic protons also authenticated the attachment of aniline fragment with indole nucleus. The downfield shift of NH signal from 10.43 ± 0.02 ppm (in reactants) to 11.5 ± 0.3 (in imines) is due to H-bonding between indolic NH and iminic nitrogen (HC$=$ N). The presence of additional signals in the aromatic region corresponding to the aniline fragment confirmed the formation of imines. The disappearance of a methine carbon at 189 ± 1 ppm (corresponding to CHO) and the appearance of a methine carbon at 155 ± 4 ppm (corresponding to HC$=$N) in broad band $^{\mathrm {13}}$ C-NMR supports our claim of successful imine formation. The XRD studies of a representative of imine (10b) ultimately confirmed the imine synthesis beyond any doubt (Fig. 2, Table 4).

Conclusion

The comparison of a variety of protocols for indole-based imine synthesis indicated high reversibility of the products to respective reactants (7-formylindole 3a–b and amines) under acidic conditions. The lemon catalyzed, $\hbox {H}_{2}\hbox {O}$-assisted, EtOH-mediated and neat conditions furnished fruitful results. The lemon catalyzed protocol, although a green approach, furnished lower yields even after the use of neutralized $\hbox {CHCl}_{{3}}$. The EtOH-mediated strategy gave fair yields that required dry reaction conditions and reflux for a long duration, which increased the cost and decreased the efficiency of reaction. The $\hbox {H}_{2}\hbox {O}$-assisted protocol proved inadequate for the synthesis of indole imines 4a–15a but produced good results for indole imines 4b–15b. Stability and good yield may be favored by the presence of three methoxy groups in case of 4,5,6-trimethoxyindole imines 4b–15b. Most efficient, economical and high yielding protocol was solvent-free synthesis, which yielded both kind of indole imines (4a–15a and 4b–15b) rapidly in excellent yields.

Experimental section

Pre-coated silica gel (0.25 mm thick layer over Al sheet, Merck, Darmstadt, Germany) TLC was used to monitor reactions. Glass column-packed silica gel (0.6–0.2 mm, 60Å mesh size, Merck) was used for purification. IR spectra were recorded on a Prestige 21 (Shimadzu, Japan) as KBr disks. UV/Vis spectra were recorded on a Thermo Spectronic (UV-1700) spectrophotometer as solution in MeOH/$\hbox {CHCl}_{{3}}$. $^{\mathrm {1}}$H-NMR and $^{\mathrm {13}}$C-NMR were recorded in $\hbox {CDCl}_{{3}}$ on a Bruker AVANCE DPX (300, 400 or 500 MHz) spectrometer (Bruker, Billarica, MA) using TMS as internal standard (s, d, t, q, dd, ddd and m stands for singlet, doublet, triplet, quarterate, double doublet, doublet of double doublet and multiplet, respectively). HR ESI was recorded on a Q-TOF Ultima API (Micromass, Waters, Milford, MA) at the Biomedical Mass Spectrometry Facility (BMSF), UNSW, Sydney (Australia). Single-crystal X-Ray data were recorded on a Bruker Kappa APEX 11 CCD diffractometer. Crystallographic data in this article have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC 1,562,669, 1,526,270 and 1,562,120 for 2a, 3b and 10b, respectively. The X-ray structure was obtained by Prof Dr Muhammad Nawaz Tahir, Department of Physics, University of Sargodha, Sargodha (Pakistan).

Representative procedure for the synthesis of indoles 2a–b

A mixture of 3,5-$\hbox {(OMe)}_{2}$ 1a or 3,4,5-$\hbox {(OMe)}_{{3}}\hbox {C}_{\mathrm {6}}\hbox {H}_{2}\hbox {NH}_{{2}}$ 1b (13.1 mmol, 3 eq) and 2-hydroxy-1,2-diphenylethanone (benzoin, 13.1 mmol, 3 eq) was stirred at 120 ºC for 2 h. The mixture was cooled to ambient temperature and stirred upon the addition of $\hbox {PhNH}_{2}$ (4.4 mmol, 1 eq) and AcOH (8.1 mL, 8.5 g, 0.141 mol, 32 eq). The resulting mixture was further stirred for 5 h at 130 ºC. The resulting mixture was cooled to ambient temperature and filtered. The crude product was washed with MeOH to afford a white solid (50–60%).

4,6-Dimethoxy-2,3-diphenyl-(1H)-indole 2a 3,5-$\hbox {(OMe)}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{3}}\hbox {NH}_{2}$ 1a (2.01 g, 13.1 mmol, 3 eq), benzoin (2.8 g,13.1 mmol, 3 eq); 2a as colorless solid (2.4 g, 56%); $\hbox {R}_{f}$: 0.3 (EtOAc/n-hexane, 2:3); mp: 240–$242\,^\circ \hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 5.56330 (274), 4.62403 (325); $\acute{\upsilon }_{\max }$ $(\hbox {cm}^{\mathrm {-1}})$: 3343 (N–H); $\delta _{\mathrm {H}}$ in ppm (300 MHz): 3.73, 3.92 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.26 (d, 1H, $J =$ 1.9 Hz, $\hbox {H}^{\mathrm {5}})$, 6.57 (1H, d, $J =$ 1.9 Hz, $\hbox {H}^{{7}})$, 7.22–7.45 (10H, m, $2 \times \hbox { Ph}$), 8.16 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (75 MHz): 55.2, 55.7 (q, OC$\hbox {H}_{{3}})$, 86.5, 92.5 (d, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{{7}})$, 113.0, 115.0 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 125.9, 126.9 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.3, 127.8, 128.5, 131.5 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 131.9, 133.0 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 135.9, 137.4 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 155.3, 157.8 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$; LR EIMS (m/z, amu): 329 [M]$^{\mathrm {+\cdot }}$ (100%), 314 [M–$\hbox {Me}^{\mathrm {\cdot }}$]$^{\mathrm {+}}$ (54%); CHNS analysis: found for $\hbox {C}_{\mathrm {22}}\hbox {H}_{\mathrm {19}}\hbox {NO}_{2}$: C (79.9%); H (5.7%), N (4.2%), requires: C (80.2%); H (5.8%); N (4.3%); Crystallographic data: Molecular Formula: $\hbox {C}_{\mathrm {22}}\hbox {H}_{\mathrm {19}}\hbox {NO}_{2}$, Molecular mass [amu]: 329.38, Crystal System: Monoclinic, a, b, c [Å]: 11.7435(16), 9.4480(12), 15.940(2), $\alpha$, $\beta$, $\gamma$ $[^\circ ]$: 90, 106.682(7), 90, Density of crystal (calc.) [g/$\hbox {cm}^{\mathrm {3}}$]: 1.291.

4,5,6-Trimethoxy-2,3-diphenyl-(1H)-indole 2b 3,4,5-$\hbox {(OMe)}_{{3}}\hbox {C}_{\mathrm {6}}\hbox {H}_{2}\hbox {NH}_{2}$ 1b (2.40 g, 13.1 mmol, 3 eq), benzoin (2.8 g, 13.1 mmol, 3 eq); 3b as off white crystalline solid (2.4 g, 50%); $\hbox {R}_\mathrm{f}$: 0.25 (EtOAc/n-hexane, 1:7); mp: 218–$220\,^\circ \hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 2.89228 (318); $\acute{{\upsilon }}_{\max }$ $(\hbox {cm}^{\mathrm {-1}})$: 3363 (N–H); $\delta _{\mathrm {H}}$ in ppm (300 MHz): 3.36, 3.72, 3.87 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.78 (1H, s, $\hbox {H}^{{7}})$, 7.23–7.48 (10H , m, $2 \times \hbox { Ph}$), 8.12 (bs, 1H, NH); $\delta _{\mathrm {C}}$ in ppm (75 MHz): 56.3, 60.9, 61.2 (q, OC$\hbox {H}_{{3}})$, 90.7 (d, $\hbox {C}^{{7}})$, 113.5, 115.8 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 126.4, 127.2 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.9, 128.0, 128.7, 131.3 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2}''}$ and $\hbox {C}^{\mathrm {3}''})$, 132.9, 133.0, (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 133.4, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 136.8, 146.7, 151.0 (all s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$; LR EIMS (m/z, amu): 359 [M]$^{\mathrm {+\cdot }}$ (100%).

General procedure for formylation of indoles 3a–b

The indole 2a/2b (3 mmol, 1 eq) was added to a stirred solution of $\hbox {POCl}_{{3}}$ (0.85 mL, 1.4 g, 9 mmol, 3 eq) in DMF (20 mL) at ambient temperature. The reaction was stirred at room temperature for 2.5 h before being quenched with chilled $\hbox {H}_{2}\hbox {O}$ (100 mL) and was basified with aq. NaOH solution (50 mL of 1 M). The resulting precipitate was filtered, washed with chilled $\hbox {H}_{2}\hbox {O}$ and dried over anhydrous silica in desiccator under reduced pressure to afford aldehyde (90–92%) as a yellow solid.

4,6-Dimethoxy-2,3-diphenyl-(1H)-indole-7-carbaldehyde 3a Indole 2a (0.99 g), 3a as yellow solid (0.99 g, 92%); $\hbox {R}_\mathrm{f}$: 0.18 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: 180–182 $^\circ \hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 3.770941 (326), 3.59740 (372); $\acute{\upsilon }_{\max } (\hbox {cm}^{\mathrm {-1}})$: 1608 (C$=$O), 3298 (N–H); $\delta _{\mathrm {H}}$ in ppm (300 MHz): 3.81, 4.00 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.15 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.23–7.36 (10H, m, 2 Ph), 10.41 (1H, s, $\hbox {D}_{2}\hbox {O}$ non-exchangeable, CHO), 10.59 (1H, bs, $\hbox {D}_{2}\hbox {O}$ exchangeable, NH); $\delta _{\mathrm {C}}$ in ppm (75 MHz): 55.5, 56.4 (q, OC$\hbox {H}_{{3}})$, 86.9 (d, $\hbox {C}^{\mathrm {5}})$, 104.2 (s, $\hbox {C}^{{7}})$, 112.76, 114.7 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 126.2, 127.3 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.5, 127.9, 128.5, 131.3 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 132.2, 133.3 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 135.4, 136.8 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 161.7, 163.0 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$, 188.2 (d, $\hbox {C}^{\mathrm {8}})$; LR EIMS (m/z, amu): 357 [M]$^{\mathrm {+\cdot }}$ (100%).

4,5,6-Trimethoxy-2,3-diphenyl-(1H)-indole-7-carbaldehyde 3b Indole 2b (1.08 g), 3b as yellow solid (0.93 g, 80%); $\hbox {R}_\mathrm{f}$: 0.65 ($\hbox {CHCl}_{{3}}$/n-hexane, 3:7); mp: $158\,^\circ \hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 3.92456 (358); $\acute{\upsilon }_{\max } (\hbox {cm}^{\mathrm {-1}})$: 1647 (C$=$O), 3347 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 3.62, 3.89, 4.10 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.26–7.40 (10H, m, 2Ph), 10.43 (1H, s, $\hbox {D}_{2}\hbox {O}$ non-exchangeable, CHO), 10.45 (1H, bs, $\hbox {D}_{2}\hbox {O}$ exchangeable, NH); $\delta _{\mathrm {C}}$ in ppm (125 MHz): 61.5 (q, OC$\hbox {H}_{{3}})$, 63.2 ($2\times$ , q, OC$\hbox {H}_{{3}})$, 107.8 (s, $\hbox {C}^{{7}})$, 114.3, 118.8 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 126.6, 127.7 (d, $\hbox {C}^{\mathrm {4}'}$ and $\hbox {C}^{\mathrm {4}''})$, 128.0, 127.8, 128.6, 131.2 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 131.8, 132.0 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.6, 135.2 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 153.1 (s, $\hbox {C}^{\mathrm {5}})$, 154.0 ($2\times$, s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$, 190.0 (d, $\hbox {C}^{\mathrm {8}})$; LR EIMS (m/z, amu): 388.3 [M $+$ 1]$^{\mathrm {+\cdot }}$ (26%); 387.3 [M]$^{\mathrm {+\cdot }}$ (100%), 372.3 [M–Me]$^{\mathrm {+\cdot }}$ (34%); crystallographic data; molecular formula: $\hbox {C}_{\mathrm {24}}\hbox {H}_{\mathrm {21}}\hbox {NO}_{{4}}$; molecular mass [amu]: 387.42; crystal system: monoclinic; a, b, c [Å]: 6.4296(7), 19.445(3), 15.858(2); ${\alpha }$, $\beta$, ${\gamma }$ $[^\circ ]$90: 96.230(6), 90; density of crystal (calc.) [g/$\hbox {cm}^{\mathrm {3}}$] 1.306.

Procedures for the synthesis of imines 4a–15a, 4b–6b, 8b–15b

Procedure-A A mixture of 4,6-dimethoxy-2,3-diphenyl-1H-indole-7-carbaldehyde 3a/4,5,6-trimethoxy-2,3-diphenyl-1H-indole-7-carbaldehyde 3b (1.0/1.1 g, 2.8 mmol, 1 eq) and $\hbox {PhNH}_{2}$ derivatives (8.4 mmol, 3 eq) in dry EtOH (30 mL) with activated molecular sieves, was refluxed under stirring for 24 h. The resulting crystals (70–90%) were thoroughly washed with MeOH to remove excess of $\hbox {PhNH}_{\mathrm {2 }}$derivatives.

Procedure-B To a well stirred mixture of 3a/3b (1.0/1.1 g, 2.8 mmol, 1 eq) and lemon juice extract (5 mL of 1.9 to 2.2 pH), the $\hbox {PhNH}_{2}$ derivatives (8.4 mmol, 3 eq) were added. The mixture was stirred at room temperature for 48 h. The reaction mixture was partitioned between $\hbox {H}_{2}\hbox {O}$ (25 mL) and neutralized $\hbox {CHCl}_{{3}} (3 \times 25 \hbox {\,mL})$. The combined organic extract was dried over anhydrous $\hbox {Na}_{2}\hbox {SO}_{{4}}$, filtered and concentrated under reduced pressure to afford reddish yellow solid (70–90%). This impure product was thoroughly washed with MeOH, to remove excess $\hbox {PhNH}_{\mathrm {2 }}$derivatives, which afforded pure bright yellow imine.

Procedure-C A homogenous mixture of 3a/3b (1.0/1.1 g, 2.8 mmol, 1 eq) and $\hbox {PhNH}_{2}$ derivatives (8.4 mmol, 3 eq) in $\hbox {CHCl}_{{3}}$ (1 mL) was refluxed in $\hbox {H}_{2}\hbox {O}$ (15 mL) for 24 h. Upon the completion of reaction, the resulting solid (70–95%) was thoroughly washed with MeOH to remove excess of $\hbox {PhNH}_{\mathrm {2 }}$derivatives.

Procedure-D A mixture of solid 3a/3b (1.0/1.1 g, 2.8 mmol, 1 eq) and $\hbox {PhNH}_{2}$ derivatives (8.4 mmol, 3 eq) was stirred at $200\,^\circ \hbox {C}$ for 24–48 h in a flask without stopper. The $\hbox {H}_{2}\hbox {O}$ produced as a by-product was collected at the neck of the flask. Upon the completion of reaction, the resulting solid (70–95%) was thoroughly washed with MeOH to remove excess of $\hbox {PhNH}_{\mathrm {2 }}$derivatives.

N-Phenyl (4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl) methanimine 4a $\hbox {PhNH}_{2}$ (0.77 mL, 1.0 g); 4a as light yellow crystals (1.04 g, 86%); $\hbox {R}_\mathrm{f}$: 0.33 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: $255--257\,^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 3.53965 (363); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1585 (C$=$N), 3329 (N–H); $\delta _{\mathrm {H}}$ in ppm (300 MHz): 3.80, 3.98 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.24 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.21–7.44 (15H, m, 3 Ph), 9.11 (1H, s, HC$=$N), 11.54 (1H, bs, NH); LR EIMS (m/z, amu): 433 [M $+$ 1]$^{\mathrm {+\cdot }}$ (25%), 432 [M]$^{\mathrm {+\cdot }}$ (100%).

N-(4-Chlorophenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 5a 4-$\hbox {ClC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.1 g); 5a as bright yellow crystals (1.18 g, 90%); $\hbox {R}_\mathrm{f}$: 0.30 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: 235 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.24303 (379); $\acute{{\upsilon }}_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1566 (C$=$N), 3338 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.78, 3.97 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.20 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.20–7.42 (14H, m, 3 Ph), 9.07 (1H, s, HC$=$N), 11.41 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.4, 55.7 (q, OC$\hbox {H}_{{3}})$, 87.7 (d, $\hbox {C}^{\mathrm {5}})$, 101.9 (s, $\hbox {C}^{{7}})$, 113.2, 114.6 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 122.5 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 126.1, 127.0 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.4, 127.8, 128.5, 131.5 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 129.2 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 130.5 (s, $\hbox {C}^{\mathrm {4}'''})$, 132.9 ($2\times$ , s, $\hbox {C}^{\mathrm {1}''}$, $\hbox {C}^{\mathrm {1}'})$, 135.9, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 151.4 (s, $\hbox {C}^{\mathrm {1}'''})$, 156.5 (d, $\hbox {C}^{\mathrm {8}})$ 159.1, 159.6 (s, $\hbox {C}^{\mathrm {4 }}$ and $\hbox {C}^{\mathrm {6}})$; CHNS analysis: found for $\hbox {C}_{\mathrm {29}}\hbox {H}_{\mathrm {23}}\hbox {ClN}_{2}\hbox {O}_{2}$: C (72.19%), H (4.56%), N (6.08%), requires: C (74.59%), H (4.96%), Cl (7.59%), N (6.00%), O (6.85%).

N-(3-Chlorophenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 6a 3-$\hbox {ClC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (0.9 mL, 1.1 g); 6a as light yellow crystals (1.02 g, 78%); $\hbox {R}_\mathrm{f}$: 0.69 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 185 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.02584 (379); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1566 (C$=$N), 3338 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.79, 3.98 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.22 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.14–7.41 (m, 14H), 9.07 (1H, s, HC$=$N), 11.36 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.4, 56.6 (q, OC$\hbox {H}_{{3}})$, 87.6 (d, $\hbox {C}^{\mathrm {5}})$, 101.7 (s, $\hbox {C}^{{7}})$, 113.0, 114.6 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 119.8, 121.3, 125.0 (d, $\hbox {C}^{\mathrm {2}'''}$, $\hbox {C}^{\mathrm {4}'''}$ and $\hbox {C}^{\mathrm {6}'''})$, 126.1, 126.9 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.4, 127.8, 128.5, 131.5 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 130.5 (d, $\hbox {C}^{\mathrm {5}'''})$, 132.8, 132.9 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.6 (s, $\hbox {C}^{\mathrm {3}'''})$, 135.9, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 151.3 (s, $\hbox {C}^{\mathrm {1}'''})$, 157.0 (d, $\hbox {C}^{\mathrm {8}})$, 159.3, 159.8 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {29}}\hbox {H}_{\mathrm {23}}\hbox {ClN}_{2}\hbox {O}_{2}$: C (72.93%), H (4.56%), N ( 5.69%), requires: C (74.59%), H (4.96%), Cl (7.59%), N (6.00%), O (6.85%).

N-(2,3-Dichlorophenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 7a 2,3-$\hbox {Cl}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{3}}\hbox {NH}_{2}$ (1.4 g); 7a as light yellow crystals (1.3 g, 92%); $\hbox {R}_\mathrm{f}$: 0.33 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.79, 3.97 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.21 (1H, s, $\hbox {H}^{\mathrm {5}})$, 6.24 (1H, dd, $J = 8.4. 2.2$ Hz, $\hbox {H}^{\mathrm {4}})$, 7.21–7.44 (12H, m, 3 Ph), 9.05 (1H, s, HC$=$N), 11.28 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.4, 56.6 (q, OC$\hbox {H}_{{3}})$, 87.6 (d, $\hbox {C}^{\mathrm {5}})$, 101.7 (s, $\hbox {C}^{{7}})$, 113.1, 114.7 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 121.1, 122.9 (d, $\hbox {C}^{\mathrm {4 }'''}$ and $\hbox {C}^{\mathrm {6}'''})$, 126.2, 127.1 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$ 127.5, 127.8 ($2\times$ , d, any two of $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 128.4 (s, $\hbox {C}^{\mathrm {3}'''})$, 130.7 (d, $\hbox {C}^{\mathrm {5}'''})$, 128.5, 131.5 ($2\times$ , d, any two of $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 132.7, 132.8 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 133.0 (s, $\hbox {C}^{\mathrm {2}'''})$, 135.8, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$ 152.5 (s, $\hbox {C}^{\mathrm {1}'''})$, 157.2 (d, $\hbox {C}^{\mathrm {8}})$ 159.5, 159.9 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {29}}\hbox {H}_{\mathrm {22}}\hbox {Cl}_{2}\hbox {N}_{2}\hbox {O}_{2}$: C (66.86%), H (4.75%), N (5.25%), requires: C (69.47%), H (4.42%), Cl (14.14%), N (5.59%), O (6.38%).

N-(4-methylphenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 8a 4-$\hbox {MeC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (0.9 g); 8a as light yellow crystals (1.28 g, 98%); $\hbox {R}_\mathrm{f}$: 0.3 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: 180 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.41288 (372); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1581 (C$=$N), 3294 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 2.38 (3H, s, $\hbox {ArC}\underline{\hbox {H}}_{{3}})$, 3.79, 3.97 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.23 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.20–7.42 (14H, m, 3 Ph), 9.11 (1H, s, HC$=$N), 11.56 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 20.9 (q, C$\hbox {H}_{{3}})$, 55.4, 56.8 (q, OC$\hbox {H}_{{3}})$, 87.9 (d, $\hbox {C}^{\mathrm {5}})$, 102.2 (s, $\hbox {C}^{{7}})$, 113.2, 114.5 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 121.1 ($2\times$ , d, $\hbox {C}^{\mathrm {3}})$, 126.0, 126.9 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.4 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 127.8, 128.5, 129.7, 131.5 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 132.5, 133.0 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.8, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 134.6 (s, $\hbox {C}^{\mathrm {4}'''})$, 150.3 (s, $\hbox {C}^{\mathrm {1}'''})$, 155.5 (d, $\hbox {C}^{\mathrm {8}})$, 158.6, 159.2 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {30}}\hbox {H}_{\mathrm {26}}\hbox {N}_{2}\hbox {O}_{2}$: C (76.80%), H (6.10%), N (5.79%), requires: C (80.69%), H (5.87%), N (6.27%), O (7.17%).

N-(3-Methylphenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 9a 3-$\hbox {MeC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (0.9 mL, 0.9 g); 9a as pale yellow crystals (1.28 g, 98%); $\hbox {R}_\mathrm{f}$: 0.78 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 193 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.16495 (363); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1573 (C$=$N), 3318 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 2.40 (3H, s, $\hbox {C}\underline{\hbox {H}}_{{3}})$, 3.73, 3.91 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.17 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.04–7.37 (14H, m, 3 Ph), 8.98 (1H, s, HC$=$N), 11.57(1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 18.5 (q, C$\hbox {H}_{{3}})$, 52.3, 56.5 (q, OC$\hbox {H}_{{3}})$, 87.8 (d, $\hbox {C}^{\mathrm {5}})$, 102.3 (s, $\hbox {C}^{{7}})$, 113.2, 114.5 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 118.0 (d, $\hbox {C}^{\mathrm {4}'''})$, 125.1 (d, $\hbox {C}^{\mathrm {2}'''})$, 126.1 (d, $\hbox {C}^{\mathrm {4 }'}$/$\hbox {C}^{\mathrm {4}''})$, 127.0 ($2\times$ , d, $\hbox {C}^{\mathrm {4 }'}$/$\hbox {C}^{\mathrm {4 }''}$ and $\hbox {C}^{\mathrm {6}'''})$, 127.5, 127.7, 128.5, 131.5 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 130.2 (d, $\hbox {C}^{\mathrm {5}'''})$, 131.7, 132.9 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 136.0, 136.7 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 148.6 (s, $\hbox {C}^{\mathrm {3}'''})$, 151.8 (s, $\hbox {C}^{\mathrm {1}'''})$, 155.6 (d, $\hbox {C}^{\mathrm {8}})$, 158.7, 159.3 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {30}}\hbox {H}_{\mathrm {26}}\hbox {N}_{2}\hbox {O}_{2}$: C (69.73%), H (5.21%), N (5.0%), requires: C (80.69%), H (5.87%), N (6.27%), O (7.17%).

N-(2,3-Dimethylphenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl) methanimine 10a 2,3-$\hbox {Me}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{3}}\hbox {NH}_{2}$ (1 mL, 0.99 g); 10a as yellow crystals (1.13 g, 88%); $\hbox {R}_\mathrm{f}$: 0.35 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: 205 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.67862 (364); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1585 (C$=$N), 3350 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 2.35, 2.39 (3H each, s, $\hbox {ArC}\underline{\hbox {H}}_{{3}})$, 3.78, 3.96 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.23 (1H, s, $\hbox {H}^{\mathrm {5}})$, 6.93 (1H, d, $J =$ 7.7 Hz, $\hbox {H}^{\mathrm {4}'''})$, 7.03 (1H, d, $J = 7.4$ Hz, $\hbox {H}^{\mathrm {6}'''})$, 7.12–7.44 (11H, m, 2 Ph and $\hbox {H}^{\mathrm {5}'''}$ ), 9.01 (1H, s, HC$=$N), 11.62 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 14.3, 20.3 (q, C$\hbox {H}_{{3}})$, 55.4, 56.8 (q, OC$\hbox {H}_{{3}})$, 87.9 (d, $\hbox {C}^{\mathrm {5}})$, 102.4 (s, $\hbox {C}^{{7}})$, 113.2, 114.5 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 121.1 (d, $\hbox {C}^{\mathrm {4}'''})$, 126.1, 126.2, 126.7, 126.9 (all d, $\hbox {C}^{\mathrm {4}'}$,$\hbox {C}^{\mathrm {4}''}$, $\hbox {C}^{\mathrm {5 }'''}$ and $\hbox {C}^{\mathrm {6}'''})$, 127.4, 127.8, 128.5, 131.5 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 129.9 (s, $\hbox {C}^{\mathrm {2 }'''}$/$\hbox {C}^{\mathrm {3}'''})$, 132.8, 132.9 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 136.1 (s, $\hbox {C}^{\mathrm {2}'''}$/$\hbox {C}^{\mathrm {3}'''})$, 136.7, 137.3 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$ 152.1 (s, $\hbox {C}^{\mathrm {1}'''})$, 155.7 (d, $\hbox {C}^{\mathrm {8}})$ 158.6, 159.2 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {31}}\hbox {H}_{\mathrm {28}}\hbox {N}_{2}\hbox {O}_{2}$: C (77.03%), H (5.12%), N (5.49%), requires: C (80.84%), H (6.13%), N (6.08%), O (6.95%).

N-(4-Methoxyphenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 11a 4-$\hbox {MeOC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.0 g); 11a as greenish yellow crystals (1.15 g, 89%); $\hbox {R}_\mathrm{f}$: 0.61 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 171 $^{\circ }\hbox { C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 3.65085 (379); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1543 (C$=$N), 3345 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.69 (3H, s, $\hbox {OC}\underline{\hbox {H}}_{{3}}$ at 4”’), 3.76, 3.89 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.14 (1H, s, $\hbox {H}^{\mathrm {5}})$, 6.87 (2H, d, $J = 8.2$, $\hbox {H}^{\mathrm {3}'''})$, 7.12–7.34 (12H, m, 2 Ph and $\hbox {H}^{\mathrm {2}'''})$, 9.03 (1H, s, HC$=$N), 11.50 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.3, 55.6, 56.8 (all q, OC$\hbox {H}_{{3}})$, 87.9 (d, $\hbox {C}^{\mathrm {5}})$, 102.2 (s, $\hbox {C}^{{7}})$, 113.1, 114.5 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 114.4 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 122.2 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 126.1, 126.9 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.4, 127.8, 128.5, 131.5 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 132.9, 133.1 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 136.1, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 146.0 (s, $\hbox {C}^{\mathrm {1}'''})$, 154.6 (d, $\hbox {C}^{\mathrm {8}})$, 154.6 (s, $\hbox {C}^{\mathrm {4}})$, 158.5, 159.1 (s, $\hbox {C}^{\mathrm {4}'''}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {30}}\hbox {H}_{\mathrm {26}}\hbox {N}_{2}\hbox {O}_{{3}}$: C (74.04%), H (4.97%), N (4.88%), requires: C (77.90%), H (5.67%), N (6.06%), O (10.38%).

N-(3,4,5-Trimethoxyphenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl) methanimine 12a 3,4,5-$\hbox {(OMe)}_{{3}}\hbox {C}_{\mathrm {6}}\hbox {H}_{2}\hbox {NH}_{2}$ (1.54 g); 12a as shiny yellow crystals (1.27 g, 87%); $\hbox {R}_\mathrm{f}$: 0.08 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: 215 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.07061 (379); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1581 (C$=$N), 3337 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.73, 3.80, 3.92 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 3.86 (6H, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.17 (1H, s, $\hbox {H}^{\mathrm {5}})$, 6.44 (2H, s, $\hbox {H}^{\mathrm {2 }'''}$ and $\hbox {H}^{\mathrm {6}'''})$, 7.12–7.36 (10H, m, 2 Ph), 8.99 (1H, s, HC$=$N), 11.33 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.4, 56.2, 56.3, 56.8, 61.1 (q, OC$\hbox {H}_{{3}})$, 87.7 (d, $\hbox {C}^{\mathrm {5}})$, 98.5 ($2\times$ , d, $\hbox {C}^{\mathrm {2 }'''}$ and $\hbox {C}^{\mathrm {6}'''})$, 101.9 (s, $\hbox {C}^{{7}})$, 113.1, 114.6 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 126.1, 127.0 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.5, 127.9, 128.5, 131.5 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 133.0 ($2\times$ , s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 136.0, 137.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 149.4 (s, $\hbox {C}^{\mathrm {1}'''})$, 153.6 (d, $\hbox {C}^{\mathrm {8}})$, 156.0 ($3\times$ , s, $\hbox {C}^{\mathrm {3}'''}$, $\hbox {C}^{\mathrm {4}'''}$, $\hbox {C}^{\mathrm {5}'''}$ ), 158.9, 159.4 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {32}}\hbox {H}_{\mathrm {30}}\hbox {N}_{2}\hbox {O}_{{5}}$: C (72.57%), H (5.09%), N (4.69%), requires: C (73.55%), H (5.79%), N (5.36%), O (15.31%).

N-(4-Nitrophenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 13a 4-$\hbox {NO}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.2 g); 13a as rusty yellow crystals (1.31 g, 98%); $\hbox {R}_\mathrm{f}$: 0.52 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:3); mp: 266 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm) 3.98706 (351); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1583 (C$=$N), 3345 N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.82, 3.98 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.08–7.29 (10H, m, 2 Ph), 7.36 (2H, d, $J = 5.0 \hbox {Hz}, \hbox {H}^{\mathrm {2}'''})$, 8.25 (2H, d, $J = 5.0 \hbox {Hz}, \hbox {H}^{\mathrm {3}'''})$, 9.14 (1H, s, HC$=$N), 11.25 (1H, bs, NH).

N-(3-Nitrophenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 14a 3-$\hbox {NO}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.2 g); 14a as orange crystals (1.1 g, 82%); $\hbox {R}_\mathrm{f}$: 0.18 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 268 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.15902 (347); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1578 (C$=$N), 3310 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.80, 3.99 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.22 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.22–7.58 (12H, m, 3 Ph), 8.03 (1H, d, $J =$ 7.8 Hz, $\hbox {H}^{\mathrm {4}'''})$, 8.10 (1H, t, $J =$ 2.0 Hz, $\hbox {H}^{\mathrm {2}'''})$, 9.13 (1H, s, HC$=$N), 11.26 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.4, 56.5 (q, OC$\hbox {H}_{{3}})$, 87.5 (d, $\hbox {C}^{\mathrm {5}})$, 101.7 (s, $\hbox {C}^{{7}})$, 113.0, 114.8 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 115.6 (d, $\hbox {C}^{\mathrm {5}'''})$, 119.5 (d, $\hbox {C}^{\mathrm {6}'''})$, 126.2, 127.1 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.5, 127.8, 128.6, 131.4 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 128.1 (d, $\hbox {C}^{\mathrm {4}'''})$, 129.7 (d, $\hbox {C}^{\mathrm {2}'''})$, 132.8, 133.0 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 135.7, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 149.1 (s, $\hbox {C}^{\mathrm {3}})$, 154.2 (s, $\hbox {C}^{\mathrm {1}})$, 157.2 (d, $\hbox {C}^{\mathrm {8}})$, 159.8, 160.2 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {29}}\hbox {H}_{\mathrm {23}}\hbox {N}_{{3}}\hbox {O}_{{4}}$: C (69.59%), H (4.57%), N (7.84%), requires: C (72.94%), H (4.85%), N (8.80%), O (13.40%).

N-(4-Bromophenyl)(4,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 15a 4-$\hbox {BrC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.5 g); 15a as dark yellow crystals (1.26 g, 88%); $\hbox {R}_\mathrm{f}$: 0.71 (EtOAc/$\hbox {CHCl}_{{3}}$/n-hexane, 1:3:6); mp: 246 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.46683 (382); $\acute{\upsilon }_{\max }$, $\hbox {cm}^{\mathrm {-1}}$ (KBr): 1578 (C$=$N), 3336 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.73, 3.91 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.15 (1H, s, $\hbox {H}^{\mathrm {5}})$, 7.09 (1H, d, $J = 8.7 \hbox {Hz}, \hbox {H}^{\mathrm {3}'''})$, 7.13–7.35 (10H, m, 2 Ph), 7.43 (1H, d, $J = 8.0 \hbox {Hz}, \hbox {H}^{\mathrm {2}'''})$, 9.00 (1H, s, HC$=$N), 11.33 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.4, 56.6 (q, OC$\hbox {H}_{{3}})$, 87.6 (d, $\hbox {C}^{\mathrm {5}})$, 101.9 (s, $\hbox {C}^{{7}})$, 113.0, 114.6 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 118.5 (s, $\hbox {C}^{\mathrm {4}'''})$, 123.0 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 126.1, 127.0 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.5, 131.5, 128.6, 131.4 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$,$\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 132.1 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 132.9, 133.0 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 135.9, 136.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 151.9 (s, $\hbox {C}^{\mathrm {1}'''})$, 156.5 (d, $\hbox {C}^{\mathrm {8}})$, 159.1, 159.6 (s, $\hbox {C}^{\mathrm {4}}$ and $\hbox {C}^{\mathrm {6}})$.

N-Phenyl(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 4b $\hbox {PhNH}_{2}$ (0.77 mL, 1.0 g); 4b as yellow crystals (1.08 g, 90%); $\hbox {R}_\mathrm{f}$: 0.44 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 168 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 5.25953 (364); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1570 (C$=$N), 3390 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 3.55, 3.90, 4.04 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.21–7.43 (15H, m, 3 Ph), 9.04 (1H, s, HC$=$N), 11.38 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (125 MHz): 61.3 , 61.6, 62.9 (q, OC$\hbox {H}_{{3}})$, 108.7 (s, $\hbox {C}^{{7}})$, 114.3, 118.8 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 121.2 ($4\times$ , d, $\hbox {C}^{\mathrm {2 }'''}$ and $\hbox {C}^{\mathrm {3}'''})$, 126.4, 127.4 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.7, 129.3, 128.6, 131.3 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 128.0 (d, $\hbox {C}^{\mathrm {4}'''})$, 131.7, 132.5 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.9, 135.7 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 142.2 (s, $\hbox {C}^{\mathrm {1}'''})$, 151.3, 152.5, 153.5 (s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 156.7 (d, $\hbox {C}^{\mathrm {8}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {30}}\hbox {H}_{\mathrm {26}}\hbox {N}_{2}\hbox {O}_{{3}}$: C (77.53%), H (5.61%), N (5.81%), requires: C (77.90%), H (5.67%), N (6.06%), O (10.38%).

N-(4-Chlorophenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 5b

-$\hbox {ClC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.1 g); 5b as light yellow crystals (1.08 g, 84%); $\hbox {R}_\mathrm{f}$: 0.60 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:4); mp: 150 $^{\circ }\hbox { C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 5.39486 (364); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1595 (C$=$N), 3350 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.50, 3.80, 3.99 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.17–7.36 (14H, m, 3 Ph), 8.95 (1H, s, HC$=$N), 11.22 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 61.4 , 61.6, 63.0 (all q, OC$\hbox {H}_{{3}})$, 108.3 (s, $\hbox {C}^{{7}})$, 114.3, 118.6 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 122.5 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 126.5, 127.4 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.8, 128.0, 128.7 (all $2\times$ , d, any three of $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3 }''})$, 129.4 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 131.3 (higher than $2\times$ , s of $\hbox {C}^{\mathrm {4 }'''}$ and d of $\hbox {C}^{\mathrm {2 }'}$/$\hbox {C}^{\mathrm {3 }'}$/$\hbox {C}^{\mathrm {2 }''}$/$\hbox {C}^{\mathrm {3}''}$ merged), 131.7, 132.6 (s, $\hbox {C}^{\mathrm {1}''}$, $\hbox {C}^{\mathrm {1}'})$, 134.6, 135.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 140.0 (s, $\hbox {C}^{\mathrm {1}'''})$, 150.9, 152.1, 153.4 (all s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 157.0 (d, $\hbox {C}^{\mathrm {8}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {30}}\hbox {H}_{\mathrm {25}}\hbox {ClN}_{2}\hbox {O}_{{3}}$: C (69.99%), H (4.76%), N (5.04%), requires: C (72.50%), H (5.07%), Cl (7.13%), N (5.64%), O (9.66%).

N-(3-Chlorophenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 6b 3-$\hbox {ClC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (0.9 mL, 1.1 g); 6b as bright yellow crystals (1.18 g, 92%); $\hbox {R}_\mathrm{f}$: 0.60 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 149 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.70187 (370); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1558 (C$=$N), 3348 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 3.59, 3.92, 4.08 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.24–7.45 (14H, m, 3 Ph), 9.02 (1H, s, HC$=$N), 11.28 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (125 MHz): 61.3 , 61.6, 63.0 (all q, OC$\hbox {H}_{{3}})$, 108.0 (s, $\hbox {C}^{{7}})$, 114.5, 118.7 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 119.7, 121.3 (d, $\hbox {C}^{\mathrm {4}'''}$ and $\hbox {C}^{\mathrm {6}'''})$, 125.7 (d, $\hbox {C}^{\mathrm {2}'''})$, 126.5, 127.5 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.7, 128.0, 128.6, 131.3 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3 }''})$, 130.3 (s, $\hbox {C}^{\mathrm {5}'''})$, 131.7, 132.5 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.4 (s, $\hbox {C}^{\mathrm {3}'''})$, 134.9, 135.6 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$ 144.0 (s, $\hbox {C}^{\mathrm {1}'''})$, 151.0, 152.0, 153.4 (all s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 157.6 (d, $\hbox {C}^{\mathrm {8}})$.

N-(4-methylphenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 8b 4-$\hbox {MeC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (0.9 g); 8b as greenish yellow crystals (1.08 g, 88%); $\hbox {R}_\mathrm{f}$: 0.63 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 154 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.18727 (369); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1589 (C$=$N), 3387 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 2.45 (3H, s, $\hbox {ArC}\underline{\hbox {H}}_{{3}})$, 3.60, 3.90, 4.09 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.30–7.50 (14H, m, 3 Ph), 9.11 (1H, s, HC$=$N), 11.45 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 21.1 (q, C$\hbox {H}_{{3}})$, 61.4 , 61.6, 63.0 (all q, OC$\hbox {H}_{{3}})$, 108.6 (s, $\hbox {C}^{{7}})$, 114.1, 118.6 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 121.1 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 126.4, 127.3 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.7 127.9, 128.6, 131.3 (all $2\times$ , d, $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3 }''})$, 129.9 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 131.8, 132.7 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.6 (s, $\hbox {C}^{\mathrm {2 }}$/$\hbox {C}^{\mathrm {7a}})$, 135.7 ($2\times$ , s, $\hbox {C}^{\mathrm {2 }}$/$\hbox {C}^{\mathrm {7a}}$ and $\hbox {C}^{\mathrm {4}'''})$, 140.1 (s, $\hbox {C}^{\mathrm {1}'''})$, 149.8, 151.4, 153.0 (all s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 156.0 (d, $\hbox {C}^{\mathrm {8}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {31}}\hbox {H}_{\mathrm {28}}\hbox {N}_{2}\hbox {O}_{{3}}$: C (77.23%), H (5.57%), N (4.84%), requires: C (78.13%), H (5.92%), N (5.88%), O (10.07%).

N-(3-Methylphenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 9b 3-$\hbox {MeC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (0.9 mL, 0.9 g); 9b as Light yellow crystals (1.18 g, 96%); $\hbox {R}_\mathrm{f}$: 0.69 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 165 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.58235 (364); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1580 (C$=$N), 3348 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 2.45 (3H, s, $\hbox {ArC}\underline{\hbox {H}}_{{3}})$, 3.56, 3.93, 4.06 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.12 (1H, d, $J = 7.5 \hbox {Hz}, \hbox {H}^{\mathrm {4}'''})$, 7.20 (1H, d, $J = 7.5 \hbox {Hz}, \hbox {H}^{\mathrm {6}'''})$, 7.22–7.47 (12H, m, 2 Ph, $\hbox {H}^{\mathrm {2}'''}$ and $\hbox {H}^{\mathrm {5}'''})$, 9.01 (1H, s, HC$=$N), 11.47 (1H, bs, NH).

N-(2,3-Dimethylphenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 10b 2,3-$\hbox {Me}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{3}}\hbox {NH}_{2}$ (1 mL, 0.99 g); 10b as dark yellow crystals (1.11 g, 88%); $\hbox {R}_\mathrm{f}$: 0.63 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 186 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.80254 (362); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1570 (C$=$N), 3336 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 2.28, 2.31 (3H each, s, $\hbox {ArC}\underline{\hbox {H}}_{{3}})$, 3.46, 3.83, 3.95 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.86 (1H, d, $J =$ 7.5 Hz, $\hbox {H}^{\mathrm {4}'''})$, 7.01 (1H, d, $J =$ 7.5 Hz, $\hbox {H}^{\mathrm {6}'''})$, 7.13–7.36 (11H, m, 2 Ph and $\hbox {H}^{\mathrm {5}'''})$, 8.87 (1H, s, HC$=$N), 11.37 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (125 MHz): 14.2, 20.2 (q, C$\hbox {H}_{{3}})$, 61.4 , 61.6, 63.0 (q, OC$\hbox {H}_{{3}})$, 108.8 (s, $\hbox {C}^{{7}})$, 114.4, 118.8 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 116.1 (d, $\hbox {C}^{\mathrm {4}'''})$, 126.4, 127.4 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.8 ($4\times$ , d, $\hbox {C}^{\mathrm {5}'''}$,$\hbox {C}^{\mathrm {6}'''}$ and any two of $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2}''}$, $\hbox {C}^{\mathrm {3}''})$, 128.6, 131.3 ($2\times$ , d, any two of $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2}''}$, $\hbox {C}^{\mathrm {3}''})$, 128.6 (s, $\hbox {C}^{\mathrm {2}'''})$, 132.0, 131.7 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 135.2, 135.7 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 138.5 (s, $\hbox {C}^{\mathrm {3}'''})$, 141.1 (s, $\hbox {C}^{\mathrm {1}'''})$, 150.5, 151.9, 153.1 (all s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 156.2 (d, $\hbox {C}^{\mathrm {8}})$. CHNS analysis: found for $\hbox {C}_{\mathrm {32}}\hbox {H}_{\mathrm {30}}\hbox {N}_{2}\hbox {O}_{{3}}$: C (77.84%), H (5.16%), N (4.81%), requires: C (78.34%), H (6.16%), N (5.71%), O (9.78%); Crystallographic data:    molecular formula: $\hbox {C}_{\mathrm {32}}\hbox {H}_{\mathrm {30}}\hbox {N}_{2}\hbox {O}_{{3}}$; molecular mass [amu]: 490.58; crystal system: triclinic; a, b, c [Å]: 10.4673(10), 11.3389(12), 11.9563(11); $\alpha$, $\beta$, $\gamma [^\circ ]$:111.371(3), 98.510(3), 90.301(3); density of crystal (calc.) [g/$\hbox {cm}^{\mathrm {3}}$]: 1.249.

N-(4-Methoxyphenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 11b 4-$\hbox {MeOC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.0 g); 11b as greenish yellow crystals (1.11 g, 87%); $\hbox {R}_\mathrm{f}$: 0.54 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 157 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.37780 (375); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1591 (C$=$N), 3336 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.47 (3H, s, $\hbox {OC}\underline{\hbox {H}}_{{3}}$ at $\hbox {C}^{\mathrm {4}'''})$, 3.78, 3.84, 3.96 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 6.91 (2H, d, $J = 8.8, \hbox {H}^{\mathrm {3}'''})$, 7.18-7.37, (12H, m, 2 Ph, and $\hbox {H}^{\mathrm {2}'''})$, 8.98 (1H, s, HC$=$N), 11.33 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 55.6, 61.4 , 61.7, 63.0 (q, OC$\hbox {H}_{{3}})$, 108.6 (s, $\hbox {C}^{{7}})$, 114.2, 118.7 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 114.5 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 122.3 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 126.4, 127.3 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.7, 127.9, 128.6, 131.3 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2}''}$, $\hbox {C}^{\mathrm {3}''})$, 131.7, 132.7 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.5, 135.7 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 140.0 (s, $\hbox {C}^{\mathrm {1}'''})$, 145.4, 151.2, 152.8 (s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 154.8 (d, $\hbox {C}^{\mathrm {8}})$, 158.2 (s, $\hbox {C}^{\mathrm {4}'''})$. CHNS analysis: found for $\hbox {C}_{\mathrm {31}}\hbox {H}_{\mathrm {28}}\hbox {N}_{2}\hbox {O}_{{3}}$: C (74.83%), H (5.07%), N (5.14%), O (10.99%). requires: C (75.59%), H (5.72%), N (5.69%), O (12.99%).

N-(3,4,5-Trimethoxyphenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 12b 2,3,4-(MeO)$_{{3}}\hbox {C}_{\mathrm {6}}\hbox {H}_{2}\hbox {NH}_{2}$ (1.54 g); 12b as dark yellow crystals (1.27 g, 89%); $\hbox {R}_\mathrm{f}$: 0.21 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 163 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.33289 (372); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1576 (C$=$N), 3379 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.50, 3.81, 3.84, 3.98 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 3.86 (6H, s, $\hbox {OC}\underline{\hbox {H}}_{\mathrm {3 }}$at $\hbox {C}^{\mathrm {3 }'''}$ and $\hbox {C}^{\mathrm {5}'''})$, 6.45 (2H, s, $\hbox {H}^{\mathrm {2 }'''}$ and $\hbox {H}^{\mathrm {6}'''})$, 7.17–7.36 (10H, m, 2 Ph), 8.94 (1H, s, HC$=$N), 11.12 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (100 MHz): 56.3 ($2\times$ , q, OC$\hbox {H}_{\mathrm {3 }}$at $\hbox {C}^{\mathrm {3 }'''}$ and $\hbox {C}^{\mathrm {5}'''})$, 61.0, 61.4, 61.7, 63.0 (q, OC$\hbox {H}_{{3}})$, 98.5 ($2\times$ , d, $\hbox {C}^{\mathrm {2 }'''}$ and $\hbox {C}^{\mathrm {6}'''})$, 108.3 (s, $\hbox {C}^{{7}})$, 114.0, 118.7 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 126.4, 127.4 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.7, 128.0, 128.6, 131.3 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 131.7, 132.6 ($2\times$ , s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.6, 135.5 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 140.0 (s, $\hbox {C}^{\mathrm {1}'''})$, 148.9, 151.7, 153.1 (s, $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 153.7(d, $\hbox {C}^{\mathrm {8}})$, 156.3 ($3\times$ , s, $\hbox {C}^{\mathrm {3}'''}$, $\hbox {C}^{\mathrm {4}'''}$, $\hbox {C}^{\mathrm {5}'''})$. CHNS analysis: found for $\hbox {C}_{\mathrm {32}}\hbox {H}_{\mathrm {30}}\hbox {N}_{2}\hbox {O}_{{5}}$: C (72.25%), H (4.99%), N (5.02%), requires: C (73.55%), H (5.79%), N (5.36%), O (15.31%).

N-(4-Nitrophenyl)(4,5,6-dimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 13b 4-$\hbox {NO}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.2 g); 13b as dark yellow crystals (1.07 g, 82%); $\hbox {R}_\mathrm{f}$: 0.62 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 168 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.04059 (375); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1584 (C$=$N), 3356 (N–H); $\delta _{\mathrm {H}}$ in ppm (400 MHz): 3.59, 3.88, 4.07 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.22–7.38 (12H, m, 2 Ph, $\hbox {H}^{\mathrm {5 }'''}$ and $\hbox {H}^{\mathrm {6}'''})$, 7.40 (1H, d, $J = 7.8 \hbox {Hz}, \hbox {H}^{\mathrm {4}'''})$, 8.34 (1H, t, $J =$ 2.0 Hz, $\hbox {H}^{\mathrm {2}'''})$, 9.10 (1H, s, HC$=$N), 11.14 (1H, bs, NH).

N-(3-Nitrophenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 14b 3-$\hbox {NO}_{2}\hbox {C}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.2 g); 14b as golden yellow crystals ( 1.25 g, 95%); $\hbox {R}_\mathrm{f}$: 0.51 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 179 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 5.16388 (388); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1576 (C$=$N), 3350 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 3.53, 3.84, 4.00 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.19–7.29 (10H, m, 2 Ph), 7.36 (2H, d, $J = 5.0 \hbox {Hz}, \hbox {H}^{\mathrm {2}'''})$, 8.25 (2H, d, $J =$ 5.0 Hz, $\hbox {H}^{\mathrm {3}'''})$, 8.96 (1H, s, HC$=$N), 10.98 (1H, bs, NH); $\delta _{\mathrm {C}}$ in ppm (125 MHz): 61.3, 61.5, 62.9 (q, OC$\hbox {H}_{{3}})$, 107.8 (s, $\hbox {C}^{{7}})$, 114.6, 118.7 (s, $\hbox {C}^{\mathrm {3}}$ and $\hbox {C}^{\mathrm {3a}})$, 121.8 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'''})$, 125.2 ($2\times$ , d, $\hbox {C}^{\mathrm {3}'''})$, 127.6, 127.7 (d, $\hbox {C}^{\mathrm {4 }'}$ and $\hbox {C}^{\mathrm {4}''})$, 127.8, 127.9, 128.7, 131.2 ($2\times$ , d, $\hbox {C}^{\mathrm {2}'}$, $\hbox {C}^{\mathrm {3}'}$, $\hbox {C}^{\mathrm {2 }''}$ and $\hbox {C}^{\mathrm {3}''})$, 131.2, 131.8 (s, $\hbox {C}^{\mathrm {1}'}$ and $\hbox {C}^{\mathrm {1}''})$, 134.7, 135.4 (s, $\hbox {C}^{\mathrm {2}}$ and $\hbox {C}^{\mathrm {7a}})$, 145.4 (s, $\hbox {C}^{\mathrm {4 }}$/$\hbox {C}^{\mathrm {5}}$/$\hbox {C}^{\mathrm {6}})$, 153.2 ($2\times$ , s, any two of $\hbox {C}^{\mathrm {4}}$, $\hbox {C}^{\mathrm {5}}$ and $\hbox {C}^{\mathrm {6}})$, 154.1 (s, $\hbox {C}^{\mathrm {4}'''})$, 159.1 (d of $\hbox {C}^{\mathrm {8}}$ and s of $\hbox {C}^{\mathrm {1}}$ merged).

N-(4-Bromophenyl)(4,5,6-trimethoxy-2,3-diphenyl-1H-indol-7-yl)methanimine 15b 4-$\hbox {BrC}_{\mathrm {6}}\hbox {H}_{{4}}\hbox {NH}_{2}$ (1.5 g); 15b as orange yellow crystals (1.31 g, 94%); $\hbox {R}_\mathrm{f}$: 0.66 ($\hbox {CHCl}_{{3}}$/n-hexane, 1:1); mp: 152 $^{\circ }\hbox {C}$; log $\varepsilon$ ($\lambda _{\max }$ in nm): 4.78249 (373); $\acute{\upsilon }_{\max }$ ($\hbox {cm}^{\mathrm {-1}})$: 1583 (C$=$N), 3356 (N–H); $\delta _{\mathrm {H}}$ in ppm (500 MHz): 3.59, 3.92, 4.07 (3H each, s, $\hbox {OC}\underline{\hbox {H}}_{{3}})$, 7.23–7.48 (14H, m, 3 Ph), 9.09 (1H, s, HC$=$N), 11.49 (1H, bs, NH). CHNS analysis: found for $\hbox {C}_{{30}}\hbox {H}_{\mathrm {25}}\hbox {BrN}_{2}\hbox {O}_{{3}}$: C (64.25%), H (4.09%), N (5.12%), requires: C (66.55%), H (4.65%), Br (14.76%), N (5.17%), O (8.86%).