ortho-silylation of 2,2 '-bis(oxazolinyl)-1,1 '-bis(diphenylphosphino)ferrocenes and remarkable effect of the silyl groups on the enantio selectivity in Pd-catalyzed asymmetric allylic alkylation

Abstract

ortho-Silylation of chiral 2,2'-bis(oxazolinyl)-1,1'-bis(diphenylphosphino)ferrocenes (1) provided monosilylated derivatives, which were employed as chiral ligands in the Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate. The major product has (S)-configuration in the reactions employing three diastereomers 1 and the monosilylated ligand derived from the (S,S,S-P,S-P)-diastereomer (up to 99% ee). In sharp contrast, the enantioselectivity was reversed to give (R)-product in the reactions with the ligands derived from the (S,S,R-P,R-P)-diastereomer (up to 96% ee). (C) 2001 Elsevier Science B.V. All rights reserved.