Reaction of 1,3-dienes with sulphur dioxide. Part 1. Thermal decomposition of 2,5-dihydrothiophen 1,1-dioxides

Abstract

Rates of decomposition of 18 substituted dihydrothiophen 1, 1-dioxides in solution (to yield the corresponding butadiene and SO₂) are reported, together with activation parameters and solvent and isotope effects. Rates are mildly accelerated by +M groups at C-3 and by alkyl substituents at C-2 but sterically retarded by bulky groups at C-3 and especially by two β-substituents. 3, 4, 5, 6-Tetrahydro-1H-cyclopenta[c]thiophen 2, 2-dioxide is especially reactive and this is attributed to strain release during fragmentation. The reactions accord in general with requirements for a chelotropic reaction.