Synthesis of Thione-Propiolic Acid Adducts

Abstract

Reaction of adamantane-2-thione with propiolic acid gave a novel type of cycloadducts, spiro[adamantane-2,2′-(1,3)-oxathiin]6-one, quantitatively. Thiocamphor and thiofenchone also reacted with propiolic acid to give the corresponding adducts stereoselectively. The observation of second-order reaction kinetics and highly stereoselective addition strongly support a cycloaddition mechanism for the thermal addition. The reaction of selenoketones with propiolic acid afforded a similar cylcoadduct. This is the first example of the reaction of monomeric thiones or selones with acetylenic acids.