Catalytic asymmetric dihydroxylation of substituted trans-stilbene derivatives: implications of the variation of enantioselectivities on the mechanism of OsO4 addition to olefins

The OsO₄ catalyzed asymmetric dihydroxylation of substituted trans-stilbene derivatives using 9-O-acetyldihydrocinchonidine as chiral ligand gives the corresponding diols with lower enantioselectivity in the case of substrates containing electron-donating and electron-withdrawing substituents. The Hammett correlations of the enantiomeric ratios exhibit non-linear plots, in accordance with the conclusion that the reaction involves a 1,3-dipolar type 3+2] cycloaddition transition state.