Base-catalyzed synthesis of 2-thioxo-2,3-dihydrothieno[2,3-d]pyrimidin-4(1H)-ones and isolation of intermediates using microwave irradiation

Abstract

A simple and fast method for the synthesis of some 3-substituted-5,6-dimethyl-2-thioxo-2,3-dihydrothieno[2,3-d]pyrimidin-4(1H)-ones has been developed via base-catalyzed cyclocondensation of ethyl 2-amino-4,5-dimethylthiophene-3-carboxylate with isothiocyanates. The uncyclized intermediates, ethyl 4,5-dimethyl-2-[(substituted carbamothioyl)amino]thiophene-3-carboxylates, were isolated when the reactions were carried out under microwave irradiation. These intermediates subsequently underwent cyclization in t-butanol in the presence of potassium t-butoxide on heating under reflux to give the desired bicyclic products