Highly Enantioselective Proline-Catalysed Direct Aldol Reaction of Chloroacetone and Aromatic Aldehydes

Ready salted proline: The combination of proline and an achiral triazabicyclodecene‐derived guanidinium salt permits, for the first time, the direct aldol reaction of chloroacetone and aromatic aldehydes (see scheme). The resulting chlorohydrins are formed with high regio‐, diastereo‐ and enantioselectivity. This procedure is experimentally simple and green, working without solvent, in test tubes placed inside a standard laboratory fridge without agitation or mechanical stirring.