Aminophosphine phosphinites of propranolol analogues as ligands for Rh-catalyzed asymmetric hydrogenation

Abstract

Chiral aminophosphine phosphinites of a series of propranolol derivatives have been prepared and their Rh chelates tested in the asymmetric hydrogenation of standard amino acid precursors. In order to optimize the stereoselectivity of the catalyst the N-substituents of the starting 1,2-amino alcohols were varied to introduce various steric and electronic effects. Direct correlations to steric constants, values of p K a or data from 31P-NMR and 13C-NMR could not be discerned. This concerns especially the pronounced difference in ee between the N-methyl 4 and N-isopropyl derivative 5. 31P NMR spectra hint at the electronic effect of the N-substitutent.