Ring-Opening Reactions of Thiophene Derivatives by the Use of the Birch Reduction

It was found that the Birch reduction of 2-(2-thienyl)alkanoic acid and subsequent alkylation with benzyl bromide resulted in the formation of 2-alkyl-3-benzylthio-3-hexenoic acid selectively. Further, the Birch reduction of a 2,3-dialkylthiophene and subsequent alkylation with benzyl bromide gave a tetrasubstituted olefin which was formed by a selective C–S bond fission between the 1 and 5 positions of the thiophene nuclei. In contrast to these results, the Birch reduction of 3-thiophenecarboxylic acid derivatives and subsequent benzylation gave 2-alkyl-4-benzylthio-3-butenoic acid which was formed by a C–S bond fission between the 1 and 2 positions of the thiophene nuclei.