Regioselective synthesis of 2-pyrazolines and pyrazoles from ethyl α-cyanocinnamates

Abstract

The cycloaddition of nitrilimines 1a–e to ethyl α-cyanocinnamate 6a furnished the 2-pyrazoline derivatives 11a–e respectively. Similar reactions of 1a–e with ethyl α-cyano-p-nitrocinnamate 6b yielded 1,3-disubstituted 4-(p-nitrophenyl)-5-ethoxycarbonylpyrazoles 14a–e, via elimination of hydrogen cyanide from their precursors, the 2-pyrazoline derivatives 13a–e, respectively. The structures of the cycloadducts 11 and 14 were supported by spectral (13C and 1H nuclear magnetic resonance and infrared) and analytical data.