Evaluation of phosphinoamidoester-derived Pd catalysts in the asymmetric allylic alkylation reaction: Theoretical studies and mechanistic insights

摘要

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 = H, R~2 = 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.