Evaluation of Phosphinoamidoester-Derived Pd Catalysts in the Asymmetric Allylic Alkylation Reaction: Theoretical Studies and Mechanistic Insights

Abstract

Two simple hemilabile P,O-coordinating phosphinoamidoester ligands 6a and 6b were synthesized and studied in the Pd(0)-catalyzed asymmetric allylic alkylation of rac-1,3-diphenylpropenyl acetate affording a highest ee of 83% ee with 6a. To gain an insight into the actual mechanism of this catalytic reactions, which had previously been investigated with a first generation family of P,O-coordinating phosphinoamido-alcohol ligands-4a and 4b-a semiempirical computational study was carried out with the Pd-allyl complexes formed from both 4a and 6a including Hitchcock's phosphinoamido- alcohol ligand 5 (R(1) = 5 H, R(2) = 5 Ph). The results of this study substantiate a working model that has previously been proposed for this reaction using hemilabile P,O-coordinating phosphinoamido- type ligands. Chirality 23:383-388, 2011. (c) 2011 Wiley-Liss, Inc.