Zemanova NBC 12-2(1 Nova Biotechnologica et Chimica 12-2 (2013) 100 DOI 10.2478/nbec-2013-0012  University of SS. Cyril and Methodius in Trnava SYNTHESIS AND REACTIONS OF NEW DERIVATIVES OF FURO[3,2-b]PYRROLE IVANA ZEMANOVÁ, RENATA GAŠPAROVÁ Department of Chemistry, Faculty of Natural Sciences, University of SS. Cyril and Methodius, J. Herdu 2, Trnava, SK-917 01, Slovak Republic (IvanaZemanova@zoznam.sk) Abstract: Synthesis of methyl 4H-furo[3,2-b]pyrrole-5-carboxylate is taken place in two step synthesis. Vilsmeier-Haack reaction of 4H-furo[3,2-b]pyrrole-5-carboxylate 1 led to methyl 2-formyl-4H-furo[3,2- b]pyrrole-5-carboxylate 4, which served as starting compound for synthesis of furo[3,2-b]pyrrole-2- aldoxime 5 and methyl 2-[(4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene)methyl]-4H-furo[3,2-b]pyrrole-5- carboxylate 7. The hydrazinolysis of 1 was prepared by carbohydrazide 2, which subsequently reacted with aldehydes to form of derivatives 3. Pyrazole derivatives 11 were prepared by the reaction of azlactone 9 with derivatives 10. Reactions were carried out under microwave irradiation or at classical heating. Key words: aldoxime, carbohydrazide, furo[3,2-b]pyrrole, microwave irradiation, hippuric acid 1. Introduction During the past few decades many results have been published in the area of the synthesis of heterocyclic compounds containing furo[3,2-b]pyrrole skeleton (PUTEROVÁ et al., 2004) due to their biological activity (KRUTOŠÍKOVÁ et al., 1994; GORUGANTULA et al., 2010). Carboxhydrazides and their derivatives are interesting class of compounds, which exhibits antitubercular (JORDÃO et al., 2011), antimicrobial (PIACZONKA et al., 2013), antifungal (TELVEKAR et al., 2012), anticonvulsant and anti-inflammatory (ULLOORA et al., 2013) activities. The present paper is a continuation of previous research, which dealt with the synthesis and reactions of furo[3,2-b]pyrrole system (GAŠPAROVÁ et al., 2005; GAŠPAROVÁ et al., 2007). 2. Material and methods Melting points of products were determined on a Kofler hot place and are uncorrected. 1H NMR spectra were obtained on a 300 MHz spectrometer VARIAN GEMINI 2000 in CDCl3 or DMSO-d6 with tetramethylsilane as the internal standard. The infrared spectra (IR) were taken on a FTIR IRAffinity-1 spectrophotometer using KBr technique. All microwave experiments were performed in a Panasonic NN-E205 type microwave oven. The apparatus was adapted for laboratory applications; n- hexane was used as coolant for the condenser. Methyl 4H-furo[3,2-b]pyrrole-5- carboxylate (4), 4H-furo[3,2-b]pyrrole-5-carbohydrazide (5) and methyl 2-formyl-4H- furo[3,2-b]pyrrole-5-carboxylate (7) were synthesized following the published procedures (KRUTOŠÍKOVÁ et al., 1994; GAJDOŠ et al., 2005). Bereitgestellt von Slovenská poľnohospodárska knižnica | Heruntergeladen 16.01.20 15:11 UTC Nova Biotechnologica et Chimica 12-2 (2013) 101 2.1. Synthesis of compounds 3a-d The mixture of 4H-furo[3,2-b]pyrrole-5-carbohydrazide 2 (1.21 mmol), 5- substituted furan-2-karbaldehyde (1.21 mmol) in ethanol (5 ml), and catalytic amount of 4-methylbenzenesulfonic acid was refluxed at 70-80°C for 0.5-1 h (Scheme 1). After cooling, the solid product was filtered off, washed with ethanol and recrystallized from ethanol. 2.1.1 N'-{[5-(4-nitrophenyl)furan-2-yl]methylidene}-4H-furo[3,2-b]pyrrole-5- carbohydrazide (3a) Yield 48 %; m. p 279-282 °C. Calcd. for C18H12N4O5 (364.31) C, 59.34; H, 3.32; N, 15.38. Found: C, 58.84; H, 3.24; N, 14.76 %. IR (KBr): 3350, 3140, 1650, 1594, 1510, 1330, 1275, 1137, 1075, 1022, 915, 852, 753, 656 cm-1. 1H NMR (DMSO-d6): 11.71 (s,1H, NH); 11.54 (s, 1H, NH); 8.75 (d, 2H, J = 7.8 Hz, H-11', H-7'); 7.78 (d, 1H, J = 4.5 Hz, H-2); 7.73 (d, 2H, J = 8.4 Hz, H-10', H-8'); 7.5 (s, 1H, H-7); 6.98 (s, 1H, H-6); 6.28 (d, 1H, J = 3 Hz, H-3'); 5.88 (s, 1H, H-3). 2.1.2 N'-{[5-(4-methylphenyl)furan-2-yl]methylidene}-4H-furo[3,2-b]pyrrole-5- carbohydrazide (3b) Yield 53 %; m. p 207-210 °C. Calcd. for C19H15N3O3 (333.34) C, 68.46; H, 4.54; N, 12.61. Found: C, 67.80; H, 4.39; N, 12.40 %. IR (KBr): 3453, 3235, 3113, 1634, 1616, 1571, 1490, 1431, 1251, 1137, 1072, 1028, 986, 819, 724 cm-1. 1H NMR (DMSO-d6): 11.58 (s,1H, NH); 11.59 (s, 1H, NH); 8.28 (s, 1H, H-7); 7.77 (d, 1H, J = 4.5 Hz, H-2); 7.70 (d, 2H, J = 7.8 Hz, H-11', H-7'); 7.31 (d, 2H, J = 8.4 Hz, H-10', H- 8'); 7.07 (d, 1H, J = 3.3 Hz, H-4'); 7.02 (m, 2H, H-6, H-3'); 6.60 (d, 1H, J = 3.9 Hz, H- 3); 2.36 (s, 3H, CH3). Bereitgestellt von Slovenská poľnohospodárska knižnica | Heruntergeladen 16.01.20 15:11 UTC 102 Zemanová, I. and Gašparová, R. 2.1.3 N'-[(5-phenylfuran-2-yl)methylidene]-4H-furo[3,2-b]pyrrole-5-carbohydrazide (3c) Yield 35 %; m. p 198-200 °C. Calcd. for C18H13N3O3 (319.31) C, 67.71; H, 4.10; N, 13.16. Found: C, 67.38; H, 3.96; N, 13.62 %. IR (KBr): 3331, 3124, 1631, 1471, 1441, 1358, 1305, 1273, 1135, 1075, 1022, 914, 806, 762, 734, 688, 646 cm-1. 1H NMR (DMSO-d6): 11.53 (br, 2H, NH); 8.28 (s, 1H, H-7); 7.70 (m, 3H, H-2, H-7', H- 11'); 7.49 (m, 3H, H-10', H-8'); 7.37 (m, 1H, H-9'); 7.02 (d, 1H, J = 3 Hz, H-4'); 7.04 (d, 1H, J = 3 Hz, H-3'); 6.99 (s, 1H, H-6); 6.60 (d, 1H, J = 3.9 Hz, H-3). 2.1.4 4-Methyl-2-{[2-({2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrol-5- yl}carbonyl)hydrazinylidene]methyl}-4H-furo[3,2-b]pyrrole-5-carboxylic acid (3d) Yield 40 %; m. p 244-246 °C. IR (KBr): 3257, 2962, 2596, 1674, 1614, 1533, 1448, 1332, 1261, 1222, 1161, 1072, 957, 796, 694 cm-1. 1H NMR (DMSO-d6): 11.84 (s,1H, NH); 11.66 (s, 1H, NH); 8.27 (s, 1H, H-7); 8.12 (m, 2H, H-7˝, H-9˝); 7.67 (m, 2H, H-10˝, H-11˝); 7.43 (s, 1H, H-6'); 7.25 (s, 1H, H-6); 7.04 (s, 1H, H-3'); 7.03(s, 1H, H-3); 6.82 (s, 1H, H-5'); 3.96 (s, 3H, CH3). 2.2 Synthesis of methyl 2-[(hydroxyimino)methyl]-4H-furo[3,2-b] pyrrole-5-carboxylate (5) Classical heating (A). To mixture of ethanol (26 ml) and water (8 ml) was added hydroxylamine hydrochloride (0.6 g, 9 mmol), sodium hydroxide (2 g, 50 mmol) and methyl 2-formyl-4H-furo[3,2-b]pyrrole-5-carboxylate 4 (0.38 g, 2 mmol) (Scheme 1). The reaction mixture was stirred at room temperature for 24 h. The precipitate was filtered off, washed with water and recrystallized from methanol. Microwave method (B). To mixture of ethanol (26 ml) and water (8 ml) was added hydroxylamine hydrochloride (0.6 g, 9 mmol) and methyl 2-formyl-4H- furo[3,2-b]pyrrole-5-carboxylate 4 (0.38 g, 2 mmol) (Scheme 1). The reaction mixture was irradiated at 90 W for 13 min. After cooling, the solid product was filtered off, washed with water and recrystallized from methanol. Yield: 50 % (A), 70 % (B); m. p 236-241 °C. Calcd. for C9H8N2O4 (208.17): C, 51.93; H, 3.87; N, 13.46. Found: C, 51.88; H, 3.89; N, 13.61 %. IR (KBr): 3290, 3145, 3084, 2960, 1678, 1458, 1315, 1273, 1220, 1124, 985, 920, 769 cm-1. 1H NMR (DMSO-d6): 12.09 (d, 1H, J = 0.6 Hz, OH); 11.88 (s, 1H, NH); 7.59 (s, 1H, H-6); 7.26 (d, 1H, J = 0.9 Hz, H-3); 6.79 (d, 1H, J = 0.7 Hz, CH); 3.81 (s, 3H, OCH3). 2.3 Methyl 2-{[(benzyloxy)imino]methyl}-4H-furo[3,2-b]pyrrole-5- carboxylate (6) The mixture of methyl 2-[(hydroxyimino)methyl]-furo[3,2-b]pyrrole-5-carboxylate 5 (3.3 g, 1.6 mmol), benzyl chloride (3.8 g, 30 mmol) and catalytic amount of sodium carbonate in acetone (200 ml) was refluxed for 48 h (Scheme 1). Sodium carbonate Bereitgestellt von Slovenská poľnohospodárska knižnica | Heruntergeladen 16.01.20 15:11 UTC Nova Biotechnologica et Chimica 12-2 (2013) 103 was filtered off and the excess of benzylchloride was distilled under reduced pressure. Ice water (100 ml) was added and the mixture was extracted with diethylether (2×50 ml). The organic layer was dried with sodium sulphate and the solvent was evaporated. Yield: 20 %; m. p 224-227 °C. Calcd. for C16H14N2O4 (298.29): C, 64.42; H, 4.73; N, 9.39. Found: C, 64.01; H, 4.69; N, 9.12 %. 1H NMR (CDCl3): 11.72 (s, 1H, NH); 7.77 (s, 1H, H-6); 7.42 (m, 6H, Ph); 6.77 (s, 1H, CH); 5.01 (s, 2H, CH2); 3.88 (s, 3H, OCH3). 2.4 Synthesis of methyl 2-[(4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene) methyl]-4H-furo[3,2-b]pyrrole-5-carboxylate (7) The mixture of methyl 2-formyl-4H-furo[3,2-b]pyrrole-5-carboxylate 4 (5 g, 26 mmol), rhodanine (7 g, 53 mmol) and sodium acetate (13 g) in glacial acetic acid (45 ml) was refluxed for 30 min. (Scheme 2). The reaction mixture was poured into water (260 ml). The separated precipitate was washed with water (140 ml), ethanol (50 ml), diethylether (20 ml), and the solid product was recrystallized from acetone. Yield: 70 %; m. p 296-298 °C. Calcd. for C12H8N2O4S2 (308.33): C, 46.74; H, 2.62; N, 9.09. Found: C, 46.44; H, 2.60; N, 8.88 %. 1H NMR δH (DMSO-d6): 13.69 (brs, 1H, NH); 12.12 (s, 1H, NH); 7.51 (s, 1H, CH); 7.29 (s, 1H, H-6); 6.87 (s, 1H, H- 3); 3.83 (s, 3H, OCH3). 2.5 Synthesis of 2-[(E)-2-carboxy-2-sulfanylethenyl]-4H-furo[3,2-b] pyrrole-5-carboxylic acid (8) The mixture of 2-[(4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene)methyl]-furo[3,2- b]pyrrole-5-carboxylate 7 (4 g, 1.5 mmol) and aqueous sodium hydroxide (7 g NaOH in 18 ml H2O) was refluxed for 30 min. (Scheme 2). After cooling, 20 M hydrochloric acid (24 ml) was added into the reaction mixture. The formed solid product was filtered off and recrystallized from methanol. Yield: 80 %; m. p >350 °C for C10H7NO5S (253.23). 1H NMR (DMSO-d6): 11.74 (s, 1H, NH); 7.56 (s, 1H, H-6); 6.99 (d, 1H, H-3); 6.74 (dd, 1H, J = 2.7 Hz, 1.1 Hz, H- 7); 3.64 (brs, 1H, SH). Bereitgestellt von Slovenská poľnohospodárska knižnica | Heruntergeladen 16.01.20 15:11 UTC 104 Zemanová, I. and Gašparová, R. 2.6 Synthesis of methyl 2-[(5-oxo-2-phenyl-1,3-oxazol-4(5H)-ylidene) methyl]-4H-furo[3,2-b] pyrrole-5-carboxylate (9) Classical heating (A). The mixture of methyl 2-formyl-4H-furo[3,2-b]pyrrole-5- carboxylate 4 (0.5 g, 2.6 mmol), hippuric acid (0.46 g, 2.6 mmol) and catalytic amount of fused potassium acetate (0.38 g, 38 mmol) in acetanhydride (12.5 ml) was refluxed for 1 h (Scheme 3). After cooling, the reaction mixture was poured into ice water. The formed solid product was filtered off, washed with water and recrystallized from ethanol. Microwave method (B). The mixture methyl 2-formyl-furo[3,2-b]pyrrole-5- carboxylate 4 (0.5 g, 2.6 mmol), hippuric acid (0.46 g, 2.6 mmol) and catalytic amount of fused potassium acetate (0.38 g, 38 mmol) in acetanhydride (12.5 ml) was irradiated at 90 W for 12 min (Scheme 3). The work-up was the same as above method A. Yield: 80 % (A), 92 % (B); m. p 324-326 °C. Calcd. for C18H12N2O5 (336.30): C, 64.29; H, 3.60; N, 8.33. Found: C, 63.96; H, 3.55; N, 8.21 %. IR (KBr): 3286, 3140, 1786, 1768, 1689, 1631, 1500, 1450, 1396, 1288, 1247, 1219, 1132, 977, 854, 761, 702 cm-1. 1H NMR (CDCl3): 11.76 (s, 1H, NH); 7.61 (m, 5H, Ph); 7.18 (s, 1H, H-6); 7.01 (s, 1H, H-3); 6.82 (s, 1H, H-7); 3.93 (s, 3H, OCH3). 2.7 Synthesis of compounds (11a-b) The mixture of methyl 2-[(5-oxo-2-phenyl-1,3-oxazol-5(4H)-ylidene)methyl]-furo [3,2-b]pyrrole-5-carboxylate 9 (1.4 mmol) and corresponding carbohydrazide (1.4 mmol), acetic acid (10 ml) and catalytic amount of fused potassium acetate (0.4 g) was irradiated at 90 W for 17 min (Scheme 3). After cooling, the solid product was filtered off, washed with water and recrystallized from ethanol. Bereitgestellt von Slovenská poľnohospodárska knižnica | Heruntergeladen 16.01.20 15:11 UTC Nova Biotechnologica et Chimica 12-2 (2013) 105 2.7.1 Methyl 2-{[1-{[(2,3-dimethyl-4H-furo[3,2-b]pyrrole-5-yl)carbonyl]imino}-5-oxo -2-phenyl-4H-imidazol-4-ylidene]methyl}-4H-furo[3,2-b]pyrrole-5-carboxylate (11a) Yield: 65 %; m. p 285-287 °C. Calcd. for C27H21N5O6 (511.49): C, 63.40; H, 4.14; N, 13.69. Found: C, 63.19; H, 4.35; N, 12.82 %. 1H NMR (DMSO-d6): 11.78 (s, 1H, NH); 11.30 (s, 1H, NH); 10.14 (s, 1H, NH); 8.09 (m, 2H, H-2', H-6'); 7.62 (m, 3H, H- 3', H-4', H-5'); 7.26 (s, 1H, H-7); 6.87 (s, 1H, H-6˝); 6.86 (d, 1H, J = 1.9 Hz, H-6); 6.68 (d, 1H, J = 1.8 Hz, H-3); 3.78 (s, 3H, OCH3); 2.28 (s, 3H, CH3); 2.04 (s, 3H, CH3). 2.7.2 Methyl 2-{[1-(phenylcarbonylimino)-5-oxo-2-phenyl-4H-imidazol-4-ylidene] methyl}-4H-furo[3,2-b]pyrrole-5-carboxylate (11b) Yield: 74 %; m. p 310-314 °C. Calcd. for C25H18N4O5 (454.43): C, 66.07; H, 3.99; N, 12.33. Found: C, 65.78; H, 3.94; N, 11.78 %. IR (KBr): 3296, 1685, 1629, 1512, 1450, 1286, 1219, 1143, 817, 758, 698 cm-1. 1H NMR (DMSO-d6): 12.07 (s, 1H, NH); 11.71 (s, 1H, NH); 8.05 (dd, 2H, J = 8.1 Hz. J = 1.5 Hz, H-2',H-6'); 7.91 (dd, 2H, J = 8.2 Hz, J = 1.5 Hz, H-3', H-5'); 7.66 (m, 6H, Ar); 7.53 (s, 1H, H-6); 7.26 (s, 1H, H-7); 6.88 (s, 1H, H-3); 3.85 (s, 3H, OCH3). 3. Results and discussion Methyl 2-formyl-4H-furo[3,2-b]pyrrole-5-carboxylate 7 was routinely prepared by condensation of furan-2-carboxaldehyde with methyl azidoacetate in methanol in the presence of sodium methoxide giving methyl 2-azido-3-(furan-2-yl)propenoate, which underwent the cyclization in boiling toluene to give methyl 4H-furo[3,2-b]pyrrole-2- carboxylate 4 (KRUTOŠÍKOVÁ et al., 1994). Compounds 3a-d were formed by reaction with carbohydrazide 2 using corresponding aldehydes in 35-53% yield. The structures of compounds 3a-d were corroborated by the presence two singlets of NH protons at 11.84 and 11.53 ppm. IR spectra of 3a-d exhibit absorption bands of carbonyl group at 1631-1674 cm-1 and absorption bands of NH group at 3258-3453 cm-1. One of the most interesting results in the study is synthesis of methyl 2- [(hydroxyimino)methyl]-4H-furo[3,2-b]pyrrole-5-carboxylate 5, which was prepared by reaction of methyl 2-formyl-4H-furo[3,2-b]pyrrole-5-carboxylate 4 with hydroxylamine hydrochloride in sodium hydroxide either by classical heating for 24 h in 50% yield or in microwave oven for 13 min. in 70% yield. The only one preparation of 4H-furo[3,2-b]pyrrole-2-aldoxime 5 has been described by GORUGANTULA et al., 2010. In their study there was described the synthesis of 4H-furo[3,2-b]pyrrole-2- aldoxime via 4-nitro-5-(2-phenylethenyl)furan-2-aldoxime palladium-catalysed reductive cyclization. Reaction of aldehyde 4 with hydroxylamine has been described as useful method of nitrile synthesis (KRUTOŠÍKOVÁ et al., 1993), but in that case aldoxime 5 has not been isolated. 1H NMR spectrum displayed doublet signal of =N- OH proton at 12.09 ppm. Doublet signal of CH proton occur at 6.79 ppm. IR spectrum of 5 shows the absorption bands of carbonyl group at 1678 cm-1 and of NH group at 3290 cm-1. Bereitgestellt von Slovenská poľnohospodárska knižnica | Heruntergeladen 16.01.20 15:11 UTC 106 Zemanová, I. and Gašparová, R. Reaction of 5 with benzyl chloride in acetone led to methyl 2- {[(benzyloxy)imino]methyl}-4H-furo[3,2-b]pyrrole-5-carboxylate 6 in yield 20 % after 48 h of refluxed. 1H NMR spectra display singlet signal of NH proton at 11.72 ppm, multiplet signal of Ph group at 7.42 ppm, singlet signal of CH2 bond at 5.01 ppm. The reaction of methyl 2-formyl-4H-furo[3,2-b]-pyrrole-5-carboxylate 4 with rhodanine afforded compound 7, which subsequently underwent hydrolysis to provide derivative 8 in 80 % yield. Compound 8 display singlet signal of NH group at 1.74 ppm and broad signal of SH group at 3.64 ppm. Signal COOH group is not occurring in the spectrum as a result of the rapid exchange hydrogen for deuterium. The reactions of azlactone 9 with carbohydrazides 10 were carried in acetic acid under microwave irradiation in the presence of potassium acetate to give compounds 11a-b in yields 65-74 %. Compounds 11a and 11b display two or three singlets at 12.01–10.14 ppm in their 1H NMR spectra due to NH group. Three singlets of NH groups of compound 11a appear at 11.78, 11.30 and 10.14 ppm. The characteristic bands observed at 1680 cm-1 and 3296 cm-1 in IR spectra correspond to the C=O and NH group. The structures of the prepared compounds were confirmed by 1H NMR and IR spectra. 4. Conclusions Derivatives 3 were obtained by the reaction of carbohydrazide 2 with heterocyclic aldehydes. Methyl 2-formyl-4H-furo[3,2-b]pyrrole-5-carboxylate 4 served as the substrate for synthesis of furo[3,2-b]pyrrole-2-aldoxime 5 as well as derivatives 7, 9. The prepared furo[3,2-b]pyrrole-2-aldoxime 5 was used as starting compound for the condensation reaction with benzyl chloride to give a compound 6. The hydrolysis of compound 7 gave 2-[2-carboxy-2-sulfanylethenyl]-4H-furo[3,2-b]pyrrole-5-carboxylic acid 8. Pyrazole derivatives 11 were prepared by the reaction of azlactone 9 with derivatives 10. Acknowledgement: This work was supported by the Slovak Research Agency under the contract No. VEGA 1/0233/12 References GAJDOŠ, P., PAVLÍKOVÁ, S., BUREŠ, F., KRUTOŠÍKOVÁ, A.: 2-[3- (Trifluoromethyl)phenyl]furo[3,2-b]pyrroles: Synthesis and reactions. Cent. Eur. J. Chem., 3, 2005, 311-325. 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