Stereoselective free radical phenylsulfenylation of a nonactivated δ-carbon atom

A stereoselective free radical introduction of a phenylthio group onto a nonactivated methyl group in the ?-position, adjacent to a prochiral carbon atom, was achieved by photolysis of (-)-menthyl benzenesulfenate in the presence of hexabutylditin and (1R, 3R, 4S, 8S)-9-phenylthiomenthol (4) was obtained with 91%optical purity. High stereoselectivity of the reaction was calculated (ab initio MP2/6-31G**) to be the consequence of the difference in the transition state eneregies (??G# = 5.08 kJ/mol) favouring 4 relative to (1R,3R,4S,8R)-9-phenylthiomenthol (5). The absolute configuration of a the new chiral carbon atom was confirmed by its correlation with the corresponding menthane-3,9-diol of known stereochemistry.