Synthesis of 4-isobutyl substituted thiophenes byGewald reaction

TheGewald reaction of 4-methyl-2-pentanone with alkyl cyanoacetates was investigated. Alkyl 2-amino-4-isobutylthiophene-3-carboxylates (4) were formed, together withbis-(2-amino-3-alkoxycarbonyl-4-isobutyl-5-thienyl)-disulfides (5) and alkyl 2-amino-4-isobutyl-5-morpholinothiophene-3-carboxylates (6). The absence of any 4-methyl substituted aminothiophene in the product mixtures came up highly unexpected. The mechanism of the reaction is discussed with respect to previously reported suggestions.