The asymmetric oxidation of prochiral sulfides in the presence of (4R,5R)-2,2-dimethyl-α,α,α′ ,α′-tetraphenyl-1,3-dioxolan-4,5-dimethanol (1) has been investigated. The best results were obtained with 1-t-butylthioisoquinoline (4) as substrate and reasons for this observation are advanced. Circular dichroism spectroscopy allowed the absolute configurations of a number of alkyl azaheterocyclic sulfoxides to be proposed.