Synergistic asymmetric activation of α,β-unsaturated carboxylic acids and its synthetic application

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While catalytic asymmetric reactions using α,β-unsaturated carboxylic acids as substrate have been examined, useful reactions could not be developed. The main reason is the catalyst decomposition due to the high acidity of carboxylic acids. However, novel optically active ligands readily prepared from naturally occurring amino acid proline were synthesized and its titanium complexes were found to be an efficient catalyst for asymmetric epoxidation of olefins in the presence of aqueous hydrogen peroxide as the stoichiometric oxidant. In the reaction of styrene derivatives, high enantioselectivity ranging from 96 to 98% ee was achieved.