Preparation of stable, camphor-derived, optically active allyl and alkyl sulfoxides and thermal epimerization of the allyl sulfoxides

Abstract

(+)-Camphor is converted by thioalkylation of the lithium enolate with allyl and alkyl p-toluenethiolsulfonates into exo-3-(allylthio)- and exo-3-(alkylthio)camphors, which upon reduction with diisobutylaluminum hydride give the corresponding exo-(allylthio)- and exo-(alkylthio)isoborneols. Oxidation of the sulfides with mchloroperbenzoic acid gives the exo-(allylsulfinyl)- and exo-(alkylsulfinyl)isoborneols in a stereochemically pure state. The configuration at sulfur in the sulfoxides is determined by X-ray crystallography of the allyl derivative to be S_S; this configuration implies that the exo-hydroxyl group at C2 controls the stereochemical outcome of the oxidation. The allylic sulfoxides are stable at room temperature, but upon heating through their melting points undergo a remarkable and generally quantitative rearrangement into the R_S epimers.