Diastereo- and Enantioselective Direct Aldol Reactions Mediated by CoCl₂/l-Proline

Significance

Metal-amino acid combinations have proved to be highly useful in catalysis; in the context of enantioselective aldol reactions zinc-proline systems received considerable attention. In this work the CoCl₂/l-proline catalyst was found to be superior to proline itself and other metal-amino acid combinations in direct aldol ­reactions. Cyclic and acyclic (including unsymmetrical) ketones were treated with aromatic and aliphatic aldehydes to give high yields of aldol products with high to excellent enantioselectivities and moderate to excellent dr values.