Thiophene S,N-ylides: a new versatile class of sulphimides

Abstract

Tetrachlorothiophene reacts with methyl, ehtyl, and phenyl azidoformates and with toluene-p-sulphonyl azide at 130–150 °C to give stable thiophene S,N-ylides. 2,5-Dichloro- and 2,5-dibromothiophene and tetrabromothiophene yield products derived by nitrene attack at the α-position. The S,N-ylides undergo ready photolysis to liberate the parent nitrene, and react with a wide variety of electron-rich dienophiles as 4π-components to give tetrachlorodihydrobenzenes with extrusion of a thionitroso compound. With dienes the ylides react either as 2π- or 4π-systems. Thus with anthracene a dihydrothiophene analogue of triptycene is generated, efficiently aromatised and de-ylidated with zinc in methanol. With dimethyl acetylenedicarboxylate the ylides yield a thiazocine by a novel ring expansion. Oxidation of the ylide system with 3-chloroperbenzoic acid gives the corresponding ylide S-oxide. Tetrachlorothiophene also reacts efficiently with diazoalkanes under rhodium acetate catalysis to give thiophene S,C-ylides, which undergo cycloaddition with nucleophilic alkenes much more slowly than their nitrogen analogues.