Regioselective Synthesis of Some Pyrazole Scaffolds Attached to Benzothiazole and Benzimidazole Moieties

Abstract

Condensation of 2-(benzothiazol-2-yl)acetonitrile (1) or 2-(1-methyl-1H-benzimidazol-2-yl)acetonitrile (2) with thiophene-2-carbaldehyde afforded the corresponding acrylonitrile derivatives3or4, respectively. The 1,3-dipolar cycloaddition reaction of the acrylonitrile3or4with nitrile-imine6gave novel pyrazole derivatives pendant to benzothiazole and benzimidazole. The pyrazoline derivative7was converted into the corresponding pyrazole derivative11via thermal elimination of hydrogen cyanide upon heating in sodium ethoxide solution. The structures of the synthesized products were confirmed by IR,1H NMR, and mass spectral techniques.