Intramolecular rearrangements: Epimerization of bicyclic vinyl tertiary alcohols via a [2,3] sulfoxide sigmatropic rearrangement

Abstract

A general method for inverting the stereochemistry of bicyclic vinyl endo alcohols such as 6 and 12 to give the corresponding exo isomers 10 and 18 is described. The procedures employ a [2,3] sulfoxide rearrangement as a key step. In the case of the norbornene alcohol 12 the intermediate sulfenate ester 13 gives the oxetane 14 rather than the expected sulfoxide 17. It was therefore prepared by thionyl chloride induced rearrangement of 12 to the allylic chloride 15 followed by displacement (PhSNa) and oxidation (m-chloroperbenzoic acid). The exo alcohol thus obtained underwent smooth anionic oxy-Cope rearrangement (KH, THF) to the cis-hydrindenone 19.