Desymmetrization of meso-hydrobenzoin using chiral, nucleophilic phosphine catalysts

The desymmetrization of meso-hydrobenzoin is described using chiral phosphine catalysts 8b-d and 9-11. The best enantioselectivity at room temperature was obtained with the newly synthesized phospholane 8c and benzoic anhydride, but the reaction is very slow. Much faster reactions, but somewhat lower enantioselectivities were observed using the bicyclic phosphine catalyst 9. To obtain product 5a with >90% ee required conditions where the ee is upgraded due to the formation of the dibenzoate 6a. Among the new phospholane catalysts, 8b has the best selectivity in the kinetic resolution of benzylic alcohols, but not at the level observed previously with catalyst 11.