Fused thia-heterocycles via isothiocyanates. Part II. A convenient synthesis of some new thieno[2,3-b]thiopyran-4-one derivatives

A facile synthesis of some methyl 5-(arylamino)-4-oxothieno[2,3-b]thiopyran-6-carboxylates 6a–g is achieved via direct reaction of deprotonated methyl 3-(2,5-dichlorothien-3-yl)-3-oxopropanoate with aryl isothiocyanates in anhydrous tetrahydrofuran (THF) under reflux. Upon saponification of 6a,b, the ester group is eliminated, most logically via decarboxylation of the presumably-formed carboxyl group. Structures of the new compounds 6a–g and 7a,b are supported by microanalytical and spectral [NMR, MS electron impact (EI) and HRMS] data.