Osmylation of chiral cis-cyclohexadienediols

A study on the osmylation of a series of chiral cis-cyclohexadienediols is described. Dihydroxylation takes place preferentially on the more electron-rich double bond. For 3-methylcyclohexa-3,5-diene-1,2-diol, 1a, the presence of protecting groups on the diol functionality is crucial in determining the degree of regio- and stereoselectivity of the reaction. X-ray crystal structure data of the major product of the osmylation of diene 1a, a protected (2S)-2-methylconduritol E, is reported. The regioselectivity of the reaction also depends on the method of osmylation used, the stoichiometric procedure being more selective than the catalytic one.