Attempted Simmons-Smith reaction on α-oxoketene dithioacetals: a new general route to 3,4-substituted and annelated thiophenes

Abstract

A new general synthesis of 3- and 3,4-substituted 4a–q, 3,4-annelated 7a–d and condensed tricyclic 9a–e thiophenes has been developed through Simmons-Smith reaction on the respective α-oxoketene dithioacetals. Extension of the reaction to α-cinnamoylketene dithioacetals 10a–e and its higher enyl analogs 13a–d, 15a–c gave the corresponding 3-styryl 11a–e and 3-di- and trienyl 14a–d, 16a–c thiophenes in highly regioselectivemanner. A probable mechanism involving an unutual intramolecular aldol condensation of sulphonium ylid formed through carbenoid methylene insertion on divalent sulfur has been suggested.