Neighbouring-group participation by sulphinyl oxygen. Part I. Norbornene sulphoxides

Abstract

3-endo-syn-Phenylsulphinylbicyclo[2,2,1]hept-5-ene-2-endo-carboxylic acid under the conditions of iodolactonisation yields, together with the expected iodolactone, a iodohydrin, of inverted (anti) configuration at the sulphur atom. From the methyl ester a sulphoxonium salt is isolated, which by hydrolysis readily yields the anti-iodohydrin-ester. The stereochemistry of the reactions, and the ¹⁸O-exchange data suggest neighbouring-group participation by sulphinyl-oxygen, followed by nucleophilic substitution by water and Walden inversion at the sulphur atom. Occurrence of a similar mechanism is proposed for the conversion of the syn-iodolactone into the anti-hydroxylactone by aqueous sodium hydroxide.