2.2.1. Synthesis of 2-(Benzothiazol-2-yl)-3-(thiophen-2-yl)acrylonitrile (3) and 2-(1-Methyl-1H-benzimidazol-2-yl)-3-(thiophen-2-yl)acrylonitrile (4)
General Procedure. To a mixture of acetonitrile 1 or 2 (10 mmol) and the thiophene 2-carbaldehyde (10 mmol) in ethanol (10 mL), piperidine (0.2 mL) was added, and the mixture was refluxed for 30 min. The formed coloured crystalline products were collected by filtration, washed with ethanol, and dried. Recrystallization from the appropriate solvent gave 3 or 4, respectively.
(1) 2-(Benzothiazol-2-yl)-3-(thiophen-2-yl)acrylonitrile (
3
). Yield (70%), mp 156–7°C; IR (KBr)
ν
2211 (C≡N), 3055 (aromatic CH) cm−1; 1H NMR [DMSO-d
6]
δ
7.34–7.60 (m, 3H), 8.04–8.18 (m, 4H), 8.68 (s, 1H); MS m/z (%) 268 (M+, 100.0), 242 (7.81), 134 (9.6), 83 (1.14). Anal. Calcd for C14H8N2S2: C, 62.66; H, 3.00; N, 10.44. Found: C, 62.75; H, 3.12; N, 10.35%.
(2) 2-(1-Methyl-1H-benzimidazol-2-yl)-3-(thiophen-2-yl)acrylonitrile (
4
). Yield (75%), mp. 100°C (methanol); IR (KBr)
ν
1609 (C=N), 2207 (C≡N), 2956 (aliphatic CH), 3087 (aromatic CH) cm−1; 1H NMR [DMSO-d
6]
δ
4.0 (s, 3H, CH3), 7.25–7.36 (m, 3H), 7.63–7.70 (m, 2H), 7.95 (d, 1H), 8.08 (d, 1H), 8.47 (s, 1H); MS m/z (%) 267 (5.96), 265 (M+, 100.0), 131 (23.95), 83 (4.47). Anal. Calcd for C15H11N3S: C, 67.90; H, 4.18; N, 15.84. Found: C, 67.82; H, 4.25; N, 15.77%.
2.2.2. Synthesis of 5-Cyanopyrazole Derivatives 7 and 9
General Procedure. Equimolar quantities of the appropriate acrylonitrile 3 or 4 (5 mmol) and
N
′
-phenylbenzohydrazonoyl chloride 5 (5 mmol) were dissolved in dry benzene (20 mL). To the resulting solution, triethylamine (0.5 mL, 5 mmol) was added and the reaction mixture was stirred for 12 h, and then the solvent was distilled under reduced pressure. The oil residue was triturated with MeOH and the solid product was collected by filtration, washed with methanol, and recrystallized from the suitable solvent to afford the corresponding pyrazole derivatives 7 and 9, respectively.
(1) 5-(Benzothiazol-2-yl)-1,3-diphenyl-4-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole-5-carbonitrile (
7
). Yield (56%), mp. 190–1°C; IR (KBr)
ν
1600 (C=N) cm−1; 1H NMR [CDCl3]
δ
5.68 (s, 1H, Pyrazole-H), 7.02–8.19 (m, 17H, ArH); MS m/z (%) 465 (2.1), 464 (8.1), 463 (M+, 14.4). Anal. Calcd for C27H18N4S2: C, 70.10; H, 3.92; N, 12.11. Found: C, 70.05; H, 3.85; N, 12.17%.
(2) 5-(1-Methyl-1H-benzimidazol-2-yl)-1,3-diphenyl-4-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole-5-carbonitrile (
9
). Yield (45%), mp. 176–7°C (ethanol); IR (KBr)
ν
1600 (C=N) cm−1; 1H NMR [CDCl3]
δ
3.71 (s, 3H, CH3), 5.66 (s, 1H, Pyrazole-H), 6.95–7.96 (m, 17H, ArH). For C28H21N5S Calcd.: C, 73.18; H, 4.61; N, 15.24. Found: C, 73.09; H, 4.66; N, 15.18%.
(3) Synthesis of 2-(1,3-diphenyl-4-(thiophen-2-yl)-1H-pyrazol-5-yl)benzothiazole (
11
). A mixture of 5-cyanopyrazole 7 (1.38 g, 3 mmol) and sodium ethoxide (prepared from sodium metal (0.07 g, 3 mmol) in EtOH (15 mL)) was heated under reflux for 1 h and then left to cool. The precipitated solid was collected by filtration, washed with water, and recrystallized from ethanol to give compound 11 in 75% yield, mp. 178–9°C (ethanol); IR (KBr)
ν
1600 (C=N) cm−1; 1H NMR [CDCl3]
δ
7.04–7.99 (m, ArH); MS m/z (%) 438 (1.6), 437 (8.1), 436 (M+, 25.4), 352 (1.3), 134 (2.8), 83 (1.6), 77 (100.0). For C26H17N3S2 Calcd.: C, 71.70; H, 3.93; N, 9.65. Found: C, 71.79; H, 3.98; N, 9.60%.