Chiral diols: a new class of additives for direct aldol reaction catalyzed by L-proline.

Nine C2 symmetric diols have been examined as additives in the L-proline-catalyzed direct aldol reaction with significant improvement in enantioselectivity, conversion efficiency, and yield. Loading of 1 mol % of (S)-BINOL leads to the desired products in up to 98% ee and 90% yield. A transition state is proposed.