Practical and simple catalytic enantioselective hydrogenation reactions to synthesize N-unprotected β-amino esters have been developed: (1) asymmetric hydrogenation of N-unprotected β-enamine ester and (2) asymmetric direct reductive amination of β-keto esters using ammonium salts. A Ru–DM-SEGPHOS complex was used as the catalyst in both cases and gave high enantioselectivity, high reactivity, and wide substrate applicability. These protocols greatly reduced reaction time and waste compared to conventional synthetic routes. The direct reductive amination route was demonstrated on a >100 kg scale.

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Lewis Acid-Catalyzed Ene Reactions of Esters of 2-Trifluoromethylpropenoic Acid.-The title reaction between the ester (I) and the alkenes (II) in the presence of EtAlCl2 proceeds without selectivity to give 1:1 mixtures of syn-and anti-isomers. In the absence of the Lewis acid, however, only polymerization of (I) is observed. The ene reaction of the ester ( V) of D-pantolactone with the olefin (VI) in the presence of TiCl4 yields (VII) as the main component without loss of a fluoride ion, together with an HCl adduct. (VII) is found to have (S)-configuration at the trifluoromethylated carbon center. -(HANZAWA, Y.; SUZUKI, M.; SEKINE, T.; MURAYAMA, T.; TAGUCHI, T.; J. Chem. Soc., Chem. Commun. (1991) 10, 721-722; Tokyo Coll. Pharm., Hachioji, Tokyo 192-03, Japan; EN)