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.

The synthetic opportunities for the preparation of optically active b-amino acids are based mainly on stoichiometric reactions with chiral auxiliaries and to a significantly lesser

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.

The enantioselective hydrogenation of E- and Z-methyl 3-acetamidobutenoate, key intermediates in the synthesis of a pharmaceutically important chiral β-amino acid, with RhI catalysts in MeOH as solvent has been investigated in detail. As chiral ligands, Et-DuPHOS, Me4-BASPHOS, DIPAMP, DIOP, HO-DIOP and Et-Ferro-TANE have been employed. T he particular role of oxyfunctionalization in some diphosphine catalysts is addressed in relation to the E/Z geometry of the substrate and the dependency of the ee on the H2 pressure.Kinetic investigations with [Rh (diphosphane) (MeOH) 2]-BF4, taking into consideration the special nature of the precatalyst {[Rh-(cod) 2] BF4/ligand versus [Rh (cod) ligand)] BF4}, NMR spectroscopic measurements and the H2 pressure dependence of the observed enantioselectivity provide evidence that the reaction proceeds via an "unsaturated route" mechanism. T his mechanism correlates to catalytic features found in the past for the hydrogenation of related unsaturated-amino acid precursors. T he influence of the temperature was similarly investigated.A nonlinear dependency of the enantiomeric ratio as a function of the reciprocal of the temperature has been found. The correlation between temperature and H2 pressure and their effects on the enantioselectivity is discussed. In general, the highest enantioselectivities for the hydrogenation of both isomeric substrates can be achieved at room temperature and below, whereas the fastest conversion takes place at 30-50℃.

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℃.