Functionalisation of alkenes by a cycloaddition–cycloreversion sequence. Part 2. Anionic cycloreversion reactions of 2,5-dihydrothiophene derivatives

Abstract

The anionic cycloreversions of the 2,5-dihydrothiophene sulphonium salts (3), (7), (12), and (16) gave the thiodienes (4), (8), (13), and (17) respectively. The 2,5-dihydrothiophenes were prepared by reduction of the corresponding sulphones (which were obtained by SO₂ addition to appropriate dienes) or by the cycloaddition of thiocarbonyl ylides to electron-deficient dipolarophiles.