The dithiole series. Part V. Reactions of 1,2-dithiole-3-thiones and 1,3-dithiolan-2-thiones with acetylenic esters and with benzyne

Abstract

5-Substituted and 4,5-disubstituted 1,2-dithiole-3-thiones react with dimethyl acetylenedicarboxylate to give 1 : 1 adducts, containing a 2-thioacylmethylene-1,3-dithiole system, and 1 : 2 adducts containing a thiopyran-4-spiro-2′-(1,3-dithiole) system. 4-Phenyl-1,2-dithiole-3-thione and 1,2-benzodithiole-3-thione give 1 : 2 adducts only. 5-Phenyl-1,2-dithiole-3-thione, with esters of acetylenic monocarboxylic acids, gives only 1 : 1 adducts and the 4-phenyl isomer gives a derivative of 1,4-bis-(1,3-dithiol-2-ylidene)but-2-ene. Related products are formed when 1,2-dithiole-3-thiones react with benzyne. 1,3-Dithiolan-2-thiones react with dimethyl acetylenedicarboxylate and with benzyne to give dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate and 1,3-benzodithiole-2-thione, respectively; a molecule of olefin is eliminated.