Mixtures of chiral monodentate phosphites, phosphonites and phosphines as ligands in Rh-catalyzed hydrogenation of N-acyl enamines: extension of the combinatorial approach

• Published in: Tetrahedron: asymmetry Vol. 15; no. 14; pp. 2165 - 2167
• Main Authors: Reetz, Manfred T, Mehler, Gerlinde, Meiswinkel, Andreas
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 26.07.2004
• ISSN: 0957-4166; 1362-511X
• DOI: 10.1016/j.tetasy.2004.04.038

By using 1:1 mixtures of two different BINOL-derived monodentate phosphites and phosphonites, dramatically enhanced enantioselectivities (ee > 97%) relative to the use of pure ligands can be obtained. Mixtures of BINOL-derived monodentate phosphites and phosphonites have been reacted with Rh-salts to form three (pre)catalysts, which are in equilibrium; two homo-combinations ML aL a and ML bL b as well as the hetero-combination ML aL b. In these cases in which the latter is more active and more enantioselective than the former, enhanced asymmetric induction results in appropriate transition metal catalyzed reactions. This principle has been extended to include mixtures of BINOL-derived monodentate phosphites, phosphonites and phosphines as ligands in the asymmetric Rh-catalyzed hydrogenation of N-acyl enamines leading to ee values of >97%.