Novel Ferrocenylphosphine‐imines Containing a Pyridine Unit as a New Family of Chiral Ligands: The Important Influence of the Position of the Pyridine N‐Atom on the Reactivity and Enantioselectivity in Palladium‐Catalyzed Asymmetric Allylic Alkylations.

Abstract

A new class of ferrocene based phosphine-imine ligands with a pyridine moiety was used in the Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl ester 5 and cyclohexenyl acetate 8, and it was found that the position of pyridine N-atom had an important influence on the catalytic activity and enantioselectivity of the Pd-complex. The Pd-complex derived from ligand (R,S-P)-1c with a 3-pyridine N-atom turned out to be an efficient catalyst, affording an allylic alkylation product with an ee of up to 99%, while the Pd-complex derived from ligand (R,S-P)-1a with a 2-pyridine N-atom surprisingly showed no activity. Using ligand (R,S-P)-1b with a 4-pyridine N-atom, an ee of 95% with 91% yield was obtained in the allylic alkylation of 1,3-diphenylprop-2en-1-yl pivalate, but no allylic alkylation product of cyclohexenyl acetate was obtained. (C) 2004 Elsevier Ltd. All rights reserved.