Proline catalysis in the asymmetric direct intermolecular aldol reactions 1,2 has recently received extraordinary attention due to its fundamental importance to the evolution of so-called organocatalysis. 3 The acidic proton of the carboxylic acid group of proline was shown to be critical for both the reactivity and stereoselectivity. 1b However, such an acidic proton has been proven to be not indispensable by the finding that chiral aminoalcohol derived proline ...
