Homogeneous asymmetric catalysis by means of chiral rhodium complexes

Synthetic and mechanistic aspects of homogeneous asymmetric hydrogenation and hydrosilylation catalyzed by rhodium complexes with chiral phosphine ligands are described. The following aspects are discussed: (i) Asymmetric reduction of α,β-enones and keto esters via hydrosilylation, (ii) Asymmetric reduction of α-keto esters and ketopantoyl lactone by hydrogénation, the latter reaction provides D-(-)-pantoyl lactone which is further converted to pantothenate, a vitamine B, (iii) Asymmetric hydrogenation of N-acyldehydro-α-amino acids; (a) remarkable effects of hydrogen pressure on the stereoselectivity, (b) crucial factors for effective asymmetric induction, (iv) Asymmetric hydrogenation of dehydropeptides; (a) efficiency of typical chiral diphosphine ligands, (b) effects of chiral centers, protecting groups and functional groups at N-and C-termini on the asymmetric induction, (c) application to stereoselective labeling of peptides, and (d) application to the synthesis of biologically active oligopeptides such as analogs of Enkephalin, a peptide hormone isolated from brain.