DIASTEREOSELECTIVITY IN THE OSMIUM-CATALYZED DIHYDROXYLATION OF ALLYLIC AMIDES AND CARBAMATES

The stereochemistry of the osmium-catalyzed dihydroxylation of a series of chiral allylic amides and carbamates has been studies. The diastereoselectivity of these reactions was found to be dependent upon the solvent and the nitrogen protecting group as well as the geometry and substitution pattern of the olefin substrate. In contrast to the erythro selectivity observed with allylic alcohols, osmylations of the allylic amides and carbamates in this study were threo selective. Stoichiometric osmylations were consistently more selective than the corresponding catalytic reactions. Control experiments suggest this is due to the presence of a second catalytic cycle based upon an osmium glycolate catalyst which accumulates as the reaction proceeds to completion. Double diastereoselective dihydroxylations of allylic carbamates were also briefly examined.