K2CO3 catalyzed regioselective synthesis of thieno[2,3-b]thiochromen-4-one oximes: access to the corresponding amine and nitroso derivatives

Abstract

An unprecedented and efficient method for the synthesis of useful thieno[2,3-b]thiochromen-4-one oximes is accomplished via a thio[3 + 2] cyclization reaction of 4-hydroxydithiocoumarins and trans-β-nitrostyrenes in the presence of 10 mol% K₂CO₃ in ethanol under reflux conditions. Furthermore, hitherto, these precursors were converted into the corresponding 2-amino thieno[2,3-b]thiochromen-4-one and 2-nitroso thieno[2,3-b]thiochromen-4-one derivatives respectively. The salient features of the present protocol are mild reaction conditions, shorter reaction times, good yields and unexpected formation of C–C and C–S bonds in a regioselective manner.