Retention of regiochemistry of allylic esters in palladium-catalyzed allylic alkylation in the presence of a MOP ligand

In the palladium-catalyzed allylic alkylation of (E)-3-substituted-2-propenyl acetates (1), 1-substituted-2-propenyl acetates (2), and 1- or 3-deuterio-2-cyclohexenyl acetate (5), which proceeds through 1,3-unsymmetrically substituted pi-allylpalladium intermediates, selective substitution at the position originally substituted with acetate was observed by use of a sterically bulky monodentate phosphine ligand, 2-(diphenylphosphino)-2'-methoxy-1,1'-binaphthyl (MeO-MOP). Studies of the structure of pi-allylpalladium complexes generated by mixing [PdCl(pi-cyclohexenyl)](2) with 1 or 2 equiv of MeO-MOP (L*) revealed that cationic bisphosphine complex [Pd(L*)(2)(pi-cyclohexenyl)]Cl-+(-) is not formed even in the presence of excess ligand but neutral monophosphine complex PdCl(L*)(pi-cyclohexenyl) (11) is formed, leaving excess ligand free, and that the exchange of the coordination site of Cl and L* in 11 is much slower than that in triphenylphosphine complex PdCl(PPh3)(pi-cyclohexenyl) (13). The slow exchange can rationalize the retention of regiochemistry in the allylic alkylation catalyzed by palladium/MeO-MOP complex.