Asymmetric Synthesis Catalyzed by Chiral Ferrocenylphosphine-Transition-Metal Complexes. 8. Palladium-Catalyzed Asymmetric Allylic Amination

Article abstract of DOI:10.1021/ja00198a048

Chiral ferrocenylphosphine ligands, represented by (R)-N-methyl-N--1-<(S)-1',2-bis(diphenylphosphino)ferrocenyl>ethylamine ((R)-(S)-1a), which have a pendant side chain bearing a hydroxy group at the terminal position, were designed and used successfully for palladium-catalyzed asymmetric allylic amination of allylic substrates containing a 1,3-disubstituted propenyl structure (RCH=CHCH(X)R: R = Ph, Me, n-Pr, i-Pr; X = OCOOEt, OCOMe, OP(O)Ph2, etc.).Reaction of the allylic substrates with benzylamine in the presence of a palladium catalyst prepared in situ from Pd2(dba)3 and (R)-(S)-1a gave high yields of amination products (RCH=CHC^*H(NHCH2Ph)R: >97percent ee (R) for R = Ph, 73percent ee (S) for R = Me, 82percent ee (S) for R = n-Pr, and 97percent ee (S) for R = i-Pr).The allylamines were converted into optically active amino acids and their derivatives.The high stereoselectivity of the ferrocenylphosphine ligand is expected to be caused by an attractive interaction between the terminal hydroxy group on the ligand and the incoming amine, which directs the nucleophilic attack on one of the ?-allyl carbons.The key role of the hydroxy group was supported by an X-ray structure analysis of a ?-allylpalladium complex and (31)P NMR studies.It was demonstrated that the pendant side chain on the ferrocenylphosphine ligand is directed toward the reaction site on palladium and the terminal hydroxy group is located at the position close to one of the ?-allyl carbon atoms and that ?-allyl group on the palladium coordinated with the ferrocenylphosphine 1a adopts one of the two possible conformational isomers with high selectivity (20/1) in an equilibrium state.