Stereochemistry of α-halogeno-sulphoxides. Part I. Inversion of chirality at the sulphinyl sulphur atom in a reaction not involving the breaking of the sulphinyl bonds at the chiral sulphur atom

Abstract

Conversion of optically active aryl methyl sulphoxides into the corresponding chloro- and bromo-methyl sulphoxides by (dichloroiodo)benzene, N-chlorobenzotriazole, or bromine, in the presence of pyridine and of silver(I) nitrate, is accompanied by inversion of configuration at the sulphur atom. In the absence of silver ions, halogenation proceeds with retention of configuration. Neither of the two processes involves substitution of the groups initially bonded to the chiral centre. The possible mechanisms are discussed.