Functionalisation of alkenes by a cycloaddition–cycloreversion sequence. Part 1. Anionic cycloreversion of tetrahydrofuran and tetrahydrothiophen derivatives

Abstract

The cycloaddition of carbonyl and thiocarbonyl ylides to cycloalkenes gives adducts whose derivatives can be made to undergo anionic cycloreversion. In this way a new synthesis of an acyclic bifunctional alkane (16) from an unactivated cycloalkene (8) has formally been achieved by way of the intermediate (14). The cycloaddition of the thiocarbonyl ylide (24) to a variety of cycloalkenes occurs in good yield. The anionic cycloreversion of the sulphonium salt (21) to give the methylthiodiene (22) serves as a model for the cycloreversion of the salt (34), but this undergoes preferential elimination in base to give products (35) and (36).