One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates.

Herein, we describe a novel approach for the practical synthesis of tetrasubstituted thiophenes . The developed method was particularly used for the facile preparation of thienyl heterocycles . The mechanism for this reaction is based on the formation of a sulfur ylide-like intermediate. It was clearly suggested by (i) the intramolecular cyclization of ketene -acetals to the corresponding thiophenes , (ii) H NMR studies of Meldrum's acid-substituted aminothioacetals , and (iii) substitution studies of the methoxy group on Meldrum's acid containing -acetals . Notably, in terms of structural effects on the reactivity and stability of sulfur ylide-like intermediates, 2-pyridyl substituted compound exhibited superior properties over those of others.