Condensed thiophen ring systems. Part 21. 5-Arylthieno[3,2-c]pyrazoles and attempted preparation of 5-arylthieno[2,3-c]pyrazoles, resulting in a novel thiophen to pyrrole transformation

Abstract

Whereas reductive cyclisation of the o-nitro-anils (1) and (2) with triethyl phosphite gave the corresponding 5-arylthieno[3,2-c]pyrazoles (6) and (7), respectively, similar treatment of the o-nitro-anils (14) and (15) gave, unexpectedly, the 1-arylpyrrole-3-carbonitriles (16) and (17), respectively, as the only isolable products. Convenient syntheses of 3-nitrothiophen-2- and 2-nitrothiophen-3-carbaldehyde are described.