Establishment and maintenance of an optimal chiral surface in cinchona-modified 1% Pt/Al2O3 for enantioselective hydrogenation of alpha-keto esters

An optimal chiral surface in the cinchona-modified Pt/Al2O3 catalytic syste m is established for fast enantioselective hydrogenation of ethyl pyruvate. A makeup protocol is used to compensate for the destructive hydrogenation of the chiral modifier, thus maintaining the optimal chiral surface over th e course of the hydrogenation reaction. Hydrogenation over the optimal surf ace (Pt-surface/modifier = 5-12) results in high enantioselectivity (94% ee ) under mild conditions (5.8 bar and 17 degrees C) with high turnover frequ ency (4 s(-1)) and turnover numbers (pyruvate/modifier>28,000, pyruvate/Pt- surface>5,500).