Deoxygenation of aromatic sulphoxides by thionyl chloride in the presence of cyclohexene. Synthesis of substituted phenoxathiins

Abstract

2,3,7,8-Tetrachlorophenoxathiin (1b) and bis-3,4-dichlorophenyl ether (2), structural analogues of the highly toxic pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (1a), have been synthesized. The preparation of (1b) by the aluminium chloride-catalysed condensation of (2) with thionyl chloride involves deoxygenation, and some aromatic chlorination also occurs. The scope of the latter reactions for the preparation of substituted phenoxathiins has been studied. Aromatic sulphoxides undergo deoxygenative chlorination upon treatment with thionyl chloride, but only deoxygenation occurs in the presence of cyclohexene, which traps the by-product chlorine.