β-Thioxo-esters. Part III. The spontaneous intramolecular cyclization of tautomeric diethyl thioacetylsuccinate. Preparation and tautomerism of 4-ethoxycarbonyl-5-methylthiophen-2(3H)-one
Abstract
The acid-catalysed reaction of diethyl acetylsuccinate (1) with hydrogen sulphide in ethanolic solution yields a mixture of ethyl (Z)-3-ethoxycarbonyl-4-mercaptopent-3-enoate (3), 4-ethoxycarbonyl-5-methylthiophen-2(3H)-one (6), and 2-ethoxy-4-ethoxycarbonyl-5-methylthiophen (7), the last two products being formed by a spontaneously occurring intramolecular cyclization condensation of the non-observed ethyl (E)-3-ethoxycarbonyl-4-mercaptopent-3-enoate (4). In appropriate acidic media (3) can be completely converted into (6) or (7).