One-pot synthesis of 2-thioxothiazolidin-4-one, thiazolidine-2,4-dione, 2-iminothiazolidin-4-one based spiro-thiolane and bicyclic chromene-thiolane hybrids via Knoevenagel, 1,4-sulfa-Michael and aldol Reactions

A simple and efficient method for the synthesis of new class of 2-thioxothiazolidin-4-one (Rhodanine), thiazolidine-2,4-dione, and 2-iminothiazolidin-4-one based spiro-thiolane hybrids is reported. The title compounds were obtained by the reaction of Knoevenagel adducts of 2-thioxothiazolidin-4-one, thiazolidine-2,4-dione, 2-iminothiazolidin-4-ones and alpha-mercaptoacetaldehyde in the presence of DABCO (20 mol %) at room temperature. The reaction proceeds via 1,4-sulfa-Michael followed by intramolecular aldol reaction to form spiro-thiolane in good to moderate yields. This method was extended for the one-pot synthesis of bicyclic chromene-thiolane hybrids to generate functionalized chromene-tetrahydrothiophene derivatives in good yield.