Regioselective Synthesis of ()-3-((Alkylamino)methylene)-2-thioxothiochroman-4-one Derivatives and Their Regioselective Cycloaddition with Alkynes.

The catalyst-free reaction between 4-hydroxydithiocoumarin and isocyanide was investigated, yielding substituted ()-3-aminomethylene-2-thioxothiochroman-4-one derivatives () regioselectively at the C-3 position of 4-hydroxydithiocoumarin. Cycloaddition of product with acetylene-1,4-dicarboxylate ester afforded adduct regioselectively in good yields. Substrates and reacted with propargyl bromide () in the presence of potassium carbonate in acetone, giving the unusual products and . DFT calculations explored the mechanism of formation and its reaction energy profile with alkynes. This protocol offers a broad substrate scope, good yields, ease of handling, catalyst-free conditions, high atom economy, regioselectivity, and a shorter reaction time.