This contribution gives an overview of the synthesis of chiral β-amino acids via asymmetric hydrogenation of the corresponding dehydroamino derivatives. Literature results are discussed regarding substrate synthesis and catalyst performance and how it is affected by substrate and catalyst structure as well as experimental parameters. A tentative mechanistic concept for the hydrogenation step is also presented. Scheme 1. Biologically active compounds with β-amino acid unitsa

Novel chiral imidazole cyclophane receptors were synthesized by highly selective N-alkylation of the imidazolyl 1Nposition of the bridged histidine diester 2 with the dibromide in the presence of NaH; these receptors exhibit good chiral recognition toward the enantiomers of L-and D-amino acid derivatives (up to KD/KL=3.52, △△G0=-23.11 kJ mol-1) in CHCl3 at 25.0℃.

A new catalyst system for the synthesis of R-aryl-substituted nitriles is reported. The bicyclic triaminophosphine P(i-BuNCH2CH2) 3N (1b) serves as an efficient and versatile ligand for the palladium-catalyzed direct α-arylation of nitriles with aryl bromides. Using ligand 1b, ethyl cyanoacetate and primary as well as secondary nitriles are efficiently coupled with a wide variety of aryl bromides possessing electron-rich, electron-poor, electron-neutral, and sterically hindered groups.

Complexes of ruthenium, iridium, and especially rhodium have been used in the homogeneously catalyzed asymmetric hydrogenation of prochiral olefins, ketones, and imines. [1] Hydrogenations are usually carried out in simple alcohols, but aromatic solvents, water, or alcohol/aromatic solvent mixtures can also be used. It has been reported that aromatic solvents such as benzene can inhibit asymmetric hydrogena-phosphatase efficiently and selectively, thereby displaying the fundamental requirements for turnover-based enzyme inactivation.