Vicinal syn dihydroxylation

The stereochemical consequences of the vicinal syn dihydroxylation of alkenes are conplementary to those of vicinal anti dihydroxylation. Show the products (indicate stereochemistry) of the vicinal... 

Syn-Dihydroxylation. When the reaction was first discovered, the syn-dihydroxylation of alkenes was carried out by using a stoichiometric amount of osmium tetroxide in dry organic solvent.56 Hoffman made the observation that alkenes could react with chlorate salts as the primary oxidants together with a catalytic quantity of osmium tetroxide, yielding syn-vicinal diols (Eq. 3.11). This catalytic reaction is usually carried out in an aqueous and tetrahydrofuran solvent mixture, and silver or barium chlorate generally give better yields.57... 

When asymmetric epoxidation of a diene is not feasible, an indirect route based on asymmetric dihydroxylation can be employed. The alkene is converted into the corresponding syn-diol with high enantioselectivity, and the diol is subsequently transformed into the corresponding trans-epoxide in a high-yielding one-pot procedure (Scheme 9.5) [20]. No cpirricrizalion occurs, and the procedure has successfully been applied to natural product syntheses when direct epoxidation strategies have failed [21]. Alternative methods for conversion of vicinal diols into epoxides have also been reported [22, 23]. 

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