Enantiomerically pure sulphinyl-4,5-dihydroisoxazoles. Part 2. Synthesis of masked and unmasked β,β′-dihydroxy ketones via stereocontrolled double aldol condensation

Reaction of stereoisomerically pure sulphinyl-4,5-dihydroisoxazoles having one or two stereocentres at C-4 and C-5 of the heterocycle with aliphatic or aromatic aldehydes resulted in highly stereoselective formal double aldol condensation; the adducts, depending on desulphurization conditions, could be converted either into optically active ββ′-dihydroxy ketones (by Raney nickel catalyzed hydrogenation in the presence of boric acid) or hydroxyisoxazolines (by Na-Hg in buffered conditions); the latter have the heterocyclic ring available for further synthetic elaboration such as highly stereoselective lithium aluminium hydride reduction to amino diols.