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

摘要

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 (MLLa)-L-a and (MLLb)-L-b as well as the hetero-combination (MLLb)-L-a. 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%. (C) 2004 Elsevier Ltd. All rights reserved.