Introduction

In recent years, green chemistry has become to one of the best approaches for green and efficient synthesis of organic compounds. The special benefits of green chemistry are using non-toxic substrate and environmentally benign solvent for the synthesis of organic compounds. Herein, our recent studies focused on developing of green catalyst [1–6] in multi-component reactions [7–10].

In the past decades, most of the researches have been focused on a study for the synthesis of heterocyclic compounds. Organic compounds containing nitrogen heterocyclic rings are important compounds in medicinal chemistry.

Recently, extensive studies have been accomplished on Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones, 1H-pyrazolo[1,2-b]phthalazine-5,10-dione and substituted dihydro-2-oxypyrroles using multi-component reactions [11]. These compounds have several biological and pharmaceutical properties [12, 13], for example anti-microbiological [14, 15], anti-tumor [16], anti-inflammatory [17]. Moreover, these compounds have been employed as calcium channel blockers, α-1a-antagonists [18], antifungal [19], anti-diabetics [20] activity. In addition, they have been used as Pl-091 [21]; many of number alkaloids with biological activities have pyrrole rings [22].

In recent decades, a number of methodologies for preparation of these compounds have been reported that is including Brønsted or Lewis acid catalysts such as Cu(OAc)2 [23], bakers’ yeast [24], TBAB [25], calcium fluoride [26], copper(II) tetrafluoroborate [27], hexaaquaaluminium(III) tetrafluoroborate [28], hydrotalcite [29], NiCl2·6H2O [30], [Btto][p-TSA] [31], PTSA/[Bmim]Br [32], CuI nanoparticles [33], InCl3 [34, 35], STA [36], ultrasound-assisted [37], SBA-Pr-SO3H [38], I2 [39], [n-Bu4N][HSO4] [40], Al(H2PO4)3 [41], oxalic acid dehydrate [42], AcOH [43] and ZrCl4 [44]. Some of these methodologies have limitations such as toxic and expensive catalysts, long time reactions, low yields, use of strongly acidic conditions, difficult work-up, high temperature. Because of their pharmaceutical and biological properties, the development of green, simple and environmentally safe methodology for the synthesis of these heterocyclic compounds has become the most important aim of our researches, and finally, we have reported saccharin as a green, economical and efficient acidic catalyst. The advantages of saccharin as a catalyst in organic compounds synthesis is environmental-friendly, green, mild, inexpensive, non-toxic. We carried out the one-pot, multi-component condensations by saccharin catalyst in excellent yields and short reaction times, and also, saccharin can be successfully used in the formation of carbon–carbon bonds as mild and green acidic catalyst in organic synthesis.

Results and discussion

In this protocol, we reported saccharin as a green acidic catalyst for an efficient and environmental-friendly methodology to diverse synthesis of 3,4-dihydropyrimidin-2-(1H)-ones derivatives via one-pot three-component condensation Biginelli reaction of aldehyde derivatives 1 (1.0 mmol), urea/thiourea 2 (1.5 mmol) and ethyl/methyl acetoacetate 3 (1.0 mmol) under thermal and solvent-free conditions (Scheme 1).

Scheme 1
scheme 1

Synthesis of 3,4-dihydropyrimidin-2-(1H)-one derivatives

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In order to optimize the reaction conditions, the synthesis of compound 4b (Table 3, entry 2) was used as a model reaction. The influence of catalyst loading on the reaction has been studied in this protocol. No product could be detected in the absence of the catalyst even after 4 h (Table 1, entry 1). Good yields were obtained in the presence of catalyst. The best catalyst loading was 15 mol% (0.027 g) (Table 1, entry 4). The higher amount of catalyst did not increase the yield of the product. (Table 1, entry 5). And the highest yield of the product was obtained in the presence of 0.027 g of catalyst, and the results are summarized in Table 1.

Table 1 Optimization of the reaction condition for the synthesis of 4b
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Also, the effect of temperature on the reaction has been studied. No product could be detected in room temperature condition (Table 2, entry 1). The reaction was investigated by changing temperature from 40 to 100 °C and the high yield of product was obtained in 80 °C temperature (Table 1, entry 4) and yields of product at different temperature are reported in Table 2.

Table 2 Effect of temperature on the synthesis of 4b
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In this regard, a series of 3,4-dihydropyrimidin-2-(1H)-ones have been synthesized with type of electron-donating and electron-withdrawing aldehydes derivatives such as Cl, Br, NO2, OH, OMe, in the presence of catalytic amount of saccharin (15 mol%) at 80 °C temperature and the results are given in Table 3.

Table 3 Saccharin catalyzed synthesis of 3,4-dihydropyrimidin-2-(1H)-one derivatives
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After the successful synthesis of 3, 4-dihydropyrimidin-2-(1H)-one derivatives, we turned our attention toward the synthesis of pyrazolo [1,2-b] phthalazine-5, 10-dione derivatives. In order to the optimal conditions, we investigated the four-component of phthalimide (5, 1.0 mmol), hydrazine monohydrate (6, 1.0 mmol), aromatic aldehydes derivatives (7, 1.0 mmol) and malononitrile (8, 1.0 mmol) in the presence of saccharin as a green and efficient catalyst. (Scheme 2).

Scheme 2
scheme 2

Synthesis of pyrazolo[1,2-b]phthalazine-5,10-dione derivatives

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In order to optimize the reaction conditions, the synthesis of compound 9c (Table 6, entry 3) was used as a model reaction. The effect of different amount of catalyst on the reaction has been studied in this protocol. No product could be detected in the absence of the catalyst even after 10 h (Table 4, entry 1). Good yields were obtained in the presence of catalyst. The best amount of catalyst was 20 mol% (0.036 g) (Table 4, entry 5). The higher amount of catalyst did not increase the yields products. (Table 4, entry 6). However, the higher yield of product is obtained with 20 mol% of catalyst and the results are summarized in Table 4.

Table 4 Optimization of the reaction condition for the synthesis of pyrazolo[1,2-b]phthalazine-5,10-dione 9c
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Also, the effect of temperature on the reaction has been investigated. No product could be detected in room temperature condition (Table 5, entry 1). The reaction was investigated by changing temperature from 40 to 110 °C and the high yield of product is obtained in 90 °C temperature (Table 5, entry 5) and yields of product at different temperature are reported in Table 5.

Table 5 Effect of the reaction temperature on the synthesis of 9c
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In order to study of this procedure, we have synthesized a series of compounds with the type of electron-donating and electron-withdrawing aldehydes derivatives such as Cl-, Br-, NO2-, OH-, OMe-substituted benzaldehydes which gave excellent yields and the generality of these four condensation reaction was studied by using of saccharin (20 mol%) via phthalimide (1.0 mmol), hydrazine monohydrate (1.0 mmol) and the type of aldehydes derivatives (1.0 mmol) malononitrile (1.0 mmol) under thermal and solvent-free conditions and the results are given in Table 6.

Table 6 Saccharin catalyzed synthesis of pyrazolo[1,2-b]phthalazine-5,10-dione derivatives under solvent-free conditions
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Also, successfully, we reported a green, mild and simple procedure for the synthesis of substituted dihydro-2-oxypyrrole by using of a one-pot four-component domino reaction via amines (aromatic or aliphatic) 10, 12 (2.0 mmol), dialkyl acetylenedicarboxylate 11 (1.0 mmol) and formaldehyde 13 (1.5 mmol) in the presence of saccharin as a green catalyst at ambient temperature with excellent yields and short reaction times (Scheme 3).

Scheme 3
scheme 3

Synthesis of substituted dihydro-2-oxypyrrole

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The generality of this four condensation reaction was studied under optimized conditions. And the reaction between aniline, dimethyl acetylenedicarboxylate (DMAD) and formaldehyde was investigation as a model reaction 14e (Table 9, entry 5), and then, the effect of various solvents was investigated for this method EtOH, H2O, CHCl3, CH2Cl2, CH3CN, MeOH. And among these solvents, MeOH (Table 7, entry 3) was found to be the best solvent for this methodology and the results are given in Table 7.

Table 7 Optimization of the reaction condition in the presence of different solvents
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The effect of different amount of catalyst was also studied in this protocol, and in the absence of catalyst, a trace amount of this product was detected after 6 h (Table 8, entry 1). Good yields were obtained in the presence of catalyst. The best amount of catalyst was 15 mol% (0.027 g) (Table 8, entry 4). The higher amount of catalyst did not increase the yields products (Table 8, entry 5), and the results are summarized in Table 8.

Table 8 Optimization of the reaction condition in the presence of different amounts of saccharin
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In order to study of this procedure, we have synthesis a series of dihydro-2-oxypyrrole derivatives with the type of aromatic or aliphatic amines with electron-donating or electron-withdrawing groups such as Cl, Br, F, Me, OMe,… and diethyl/dimethyl acetylenedicarboxylate with formaldehyde under ambient temperature in MeOH which gave excellent yields and the results are given in Table 9. The proposed mechanism for the synthesis of 3,4-dihydropyrimidin-2-(1H)-one derivatives, 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives is shown in Schemes 4 and 5 and that of dihydro-2-oxypyrroles is shown in Scheme 6.

Table 9 Synthesis of dihydro-2-oxypyrrole derivatives
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Scheme 4
scheme 4

Proposed mechanistic route for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones

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Scheme 5
scheme 5

Proposed mechanistic route for the synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives

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Scheme 6
scheme 6

Proposed mechanistic route for the synthesis of substituted dihydro-2-oxypyrrole

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Comparison of catalytic ability some of catalysts reported in the literature for synthesis of 3, 4-dihydropyrimidin-2-(1H)-one derivative, 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives is given in Tables 10 and 11 and that of substituted dihydro-2-oxypyrrole is given in Table 12.

Table 10 Comparison of catalytic ability some of catalysts reported in the literature for synthesis of 3,4-dihydropyrimidin-2-(1H)-ones derivatives
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Table 11 Comparison of catalytic ability some of catalysts reported in the literature for synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives
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Table 12 Comparison of catalytic ability some of catalysts reported in the literature for synthesis of substituted dihydro-2-oxypyrrole
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Experimental

General

Melting points of all compounds were determined using an Electro thermal 9100 apparatus. Also, nuclear magnetic resonance, 1H NMR spectra were recorded on a Bruker DRX-400 Avance instruments with CDCl3 or DMSO-d6 as solvents. In this article, all reagents and solvents were purchased from Merck, Fluka and Acros chemical companies and were used without further purification.

General procedure for preparation of 3,4-dihydropyrimidin-2-(1H)-one derivatives (4a–t)

A mixture of aldehydes derivatives (1, 1.0 mmol) and urea/thiourea (2, 1.5 mmol), ethyl/methyl acetoacetate (3, 1.0 mmol) under solvent-free conditions was heated for appropriate time in the presence of saccharin (15 mol%) at 80 °C (Table 3). After completion of the reaction (by thin-layer chromatography TLC), the mixture was cooled to r.t. and cold water was added and the precipitated was separated with filtration and solid was recrystallized from ethanol to afford the pure products (4a–t). The products have been characterized by melting points and 1H NMR spectroscopy. Spectra data of selected and known products are represented below:

5-Methoxycarbonyl-6-methyl-4-(2-chloro-phenyl)-3,4-dihydropyrimidin-2(1H)-one (4a)

Yellow solid, mp: 248–250 °C; 1H NMR (400 MHz, DMSO-d6): 2.31(3H, s, CH3), 3.46 (3H, s, OCH3), 5.62 (1H, s, CHN), 7.28–7.34 (3H, m, ArH), 7.42 (1H, d, J = 7.2 Hz, ArH), 7.72 and 9.36 (2H, 2s, 2NH).

5-Ethoxycarbonyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (4b)

Yellow solid, mp: 201–203 °C; 1H NMR (400 MHz, DMSO-d6): 1.10 (3H, t, J = 7.2 Hz, CH3CH2), 2.26 (3H, s, CH3), 3.99 (2H, q, J = 7.2 Hz, CH2O), 5.15 (1H, s, CHN), 7.26 (3H, d, J = 7.2 Hz, ArH),7.33 (2H, t, J = 7.2 Hz, ArH), 7.76 and 9.21(2H, 2s, 2NH).

5-Methoxycarbonyl-6-methyl-4-(4-nitro-phenyl)-3,4-dihydropyrimidin-2(1H)-one (4e)

Brown solid, mp: 213–214 °C; 1H NMR (400 MHz, DMSO-d6): 2.28 (3H, s, CH3), 3.55 (3H, s, OCH3), 5.28 (1H, s, CHN), 7.52 (2H, d, J = 8.4 Hz, ArH), 8.22 (2H, d, J = 8.8 Hz, ArH), 7.93 and 9.40 (2H, 2s, 2NH).

5-Ethoxycarbonyl-6-methyl-4-(4-methylphenyl)-3,4-dihydropyrimidin-2(1H)-one (4n)

Yellow solid, mp: 203–205 °C; 1H NMR (400 MHz, DMSO-d6): 1.11 (3H, t, J = 7.2 Hz, CH3CH2), 2.26 (6H, d, J = 9.2 Hz, 2CH3), 3.99 (2H, q, J = 7.2 Hz, CH2O), 5.11 (1H, s, CHN), 7.13 (4H, s, ArH), 7.70 and 9.17(2H, 2s, 2NH).

5-Ethoxycarbonyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-thione (4p)

White solid, mp: 206–208 °C; 1H NMR (400 MHz, DMSO-d6): 1.11 (3H, t, J = 7.2 Hz, CH3CH2), 2.31 (3H, s, CH3), 4.02 (2H, q, J = 7.2 Hz, CH2O), 5.19 (1H, s, CHN), 7.23 (2H, d, J = 7.2 Hz, ArH), 7.28 (1H, t, J = 7.2 Hz, ArH), 7.36 (2H, t, J = 7.2 Hz, ArH), 9.68 and 10.36 (2H, 2s, 2NH).

General procedure for preparation of pyrazolo [1,2-b]phthalazine-5,10-dione derivatives (9a–r)

A mixture of phthalimide (5, 1.0 mmol), hydrazine monohydrate (6, 1.0 mmol) and saccharin (20 mol%) was heated for 2 h at 90 °C. Then aromatic aldehyde (7, 1.0 mmol) and malononitrile (8, 1.0 mmol) were added and the mixture was heated for the appropriate time (Table 6). After completion of the reaction (by thin-layer chromatography TLC), the mixture was cooled to rt the solid products were filtered and then were recrystallized from ethanol to give pure compounds (9a–r). The products have been characterized by melting points and 1H NMR spectroscopy. Spectra data of selected and known are represented below:

3-Amino-1-(2-thenaldehyde)-5,10-dihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine-2-carbonitrile (9a)

Brown solid, mp: 242–244 °C; 246–248 °C; 1H NMR (400 MHz, DMSO-d6): 6.09 (1H, s, CHAr), 6.88–7.30 (4H, m, ArH), 7.96–8.28 (6H, m, NH2 and ArH).

3-Amino-1-(3-methoxyphenyl)-5,10-ihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine-2-carbonitrile (9 h)

Brown solid, mp: 250–252 °C; 1H NMR (400 MHz, DMSO-d6): 3.34 (3H, s, OCH3), 6.09 (1H, s, CHAr), 6.88–7.30 (4H, m, ArH), 7.83–8.26 (6H, m, NH2 and ArH).

3-Amino-1-(3,4,5-trimethoxyphenyl)-5,10-dihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine2-carbonitrile (9m)

Yellow solid, mp: 253–255 °C; 1H NMR (400 MHz, DMSO-d6): 3.66 (3H, s, OCH3), 3.76 (6H, s, 2 OCH3), 6.07 (1H, s, CHAr), 6.78 (2H, s, ArH), 7.89–8.29 (6H, m, NH2 and ArH).

3-Amino-1-(4-fluorophenyl)-5,10-dihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine-2carbonitrile (9n)

Yellow solid, mp: 264–266 °C; 1H NMR (400 MHz, DMSO-d6): 6.17 (1H, s, CHAr), 7.20 (2H, t, J = 8.8 Hz, ArH), 7.53–7.57 (2H, m, ArH), 7.96–8.26 (6H, m, NH2 and ArH).

3-Amino-1-(4-methylphenyl)-5,10-dihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine-2-carbonitrile (9o)

Yellow solid, mp: 254–256 °C; 1H NMR (400 MHz, DMSO-d6): 2.30 (3H, s, CH3), 6.10 (1H, s, CHAr), 7.18 (2H, d, J = 8.0 Hz, ArH), 7.34 (2H, d, J = 8.0 Hz, ArH), 7.97–8.28 (6H, m, NH2 and ArH).

General procedure for preparation of substituted dihydro-2-oxypyrrole (14a–s)

A mixture of amine (10, 1.0 mmol) and dialkyl acetylenedicarboxylate (11, 1.0 mmol) was stirred in MeOH (3 mL) for 15 min. Next, amine (12, 1.0 mmol) and formaldehyde (13, 1.5 mmol) and saccharin (15 mol%) were added and the reaction was stirred for appropriate time (Table 9). After completion of the reaction (by thin-layer chromatography TLC), the mixture was separated with filtration and the solid washed with ethanol (3 × 2 mL) with no column chromatographic separation to give pure compounds (14a–s). The products have been characterized by melting points and 1H NMR spectroscopy. Spectra data of selected and known products are represented below:

Methyl 4-(4-fluoroyphenylamino)-1-(4-fluorophenyl)-2,5-dihydro-5-oxo-1H-pyrrole-3-carboxylate (14c)

White solid, mp: 163–165 °C; 1H NMR (400 MHz, CDCl3): 3.79 (3H, s, OCH3), 4.52 (2H, CH2–N), 7.04 (2H, t, J = 8.4 Hz, ArH), 7.08–7.16 (4H, m, ArH), 7.73–7.79 (2H, m, ArH), 8.05 (1H, s, NH).

Methyl 4-(4-methylphenylamino)-1-(4-methylphenyl)-2,5-dihydro-5-oxo-1H-pyrrole-3-carboxylate (14g)

White solid, mp: 176–178 °C; 1H NMR (400 MHz, CDCl3): 2.36 (3H, s, 2CH3), 3.77 (3H, s, OCH3), 4.52 (2H, CH2–N), 7.06 (2H, d, J = 8.4 Hz, ArH), 7.14 (2H, d, J = 8.4 Hz, ArH), 7.21 (2H, d, J = 8.4 Hz, ArH), 7.68 (2H, d, J = 8.8 Hz, ArH), 8.03 (1H, s, NH).

Ethyl 4-(4-methylphenylamino)-1-(4-methylphenyl)-2,5-dihydro-5-oxo-1H-pyrrole-3-carboxylate (14h)

White solid, mp: 130–132 °C; 1H NMR (400 MHz, CDCl3): 1.25 (3H, t, J = 7.2 Hz, CH2CH3), 2.37 (6H, s, 2CH3), 4.23 (2H, q, J = 7.2 Hz, 2CH2CH3), 4.53 (2H, s, CH2–N), 7.06 (2H, d, J = 8.4 Hz, ArH), 7.1 (2H, d, J = 8.4 Hz, ArH), 7.21 (2H, d, J = 8.4 Hz, ArH), 8.00 (1H, s, NH).

Methyl 4-(4-methoxyphenylamino)-1-(4-methoxyphenyl)-2,5-dihydro-5-oxo-1H-pyrrole-3-carboxylate (14i)

Pale yellow solid, mp: 175–176 °C; 1H NMR (400 MHz, CDCl3): 3.77 (3H, s, CH3), 3.83 (6H, s, 2OCH3), 4.50 (2H, CH2–N), 6.89 (4H, d, J = 17.6 Hz, ArH), 7.13 (1H, s, ArH), 7.68 (1H, s, ArH), 8.03 (1H, s, NH).

Ethyl 4-(4-methoxyphenylamino)-1-(4-methoxyphenyl)-2,5-dihydro-5-oxo-1H-pyrrole-3-carboxylate (14j)

Pale yellow solid, mp: 152–154 °C; 1H NMR (400 MHz, CDCl3): 1.26 (3H, t, J = 7.2 Hz, CH2CH3), 3.83 (6H, s, 2OCH3), 4.23 (2H, q, J = 7.2 Hz, CH2CH3), 4.50 (2H, s, CH2–N), 6.87 (2H, d, J = 8.8 Hz, ArH), 6.93 (2H, d, J = 8.8 Hz, ArH), 7.12 (2H, d, J = 8.8 Hz, ArH), 7.69 (2H, d, J = 8.8 Hz, ArH), 8.02 (1H, s, NH).

Conclusion

In summary, we have studied the use of saccharin as a green, economical and efficient catalyst for the multi-component synthesis of 3,4-dihydropyrimidin-2-(1H)-one derivatives and pyrazolo [1, 2-b] phthalazine-5,10-dione derivatives and dihydro-2-oxypyrrole derivatives from starting materials. And we reported saccharin as a solid acid catalyst which has developed a new procedure in the field of green approach which has important benefits such as non-toxic, eco-friendly, green, high efficiently, environmentally benign nature, high catalytic activity, low cost.