One pot synthesis of tetrasubstituted thiophenes: [3 + 2] annulation strategy

Abstract

A simple, efficient and economical synthesis of dimethyl 3-amino-5-(2-oxo-2-arylethyl)thiophene-2,4-dicarboxylates has been reported by ring opening of methyl 3-amino-6-aryl-4-oxo-4H-thieno[3,2-c]pyran-2-carboxylates by alkoxide ions. Pyranothiophenes have been obtained by the reaction of methyl thioglycolate and 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles in the presence of triethylamine. A one-pot multicomponent protocol for the synthesis of tetrasubstituted thiophenes has been developed by reaction of 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles and methyl thioglycolate in the presence of sodium methoxide in excellent yields. The structure of the isolated compound was confirmed by single crystal X-ray diffraction and spectroscopic studies.