Mechanism and Origins of Nucleophile‐Controlled Regioselectivity of Palladium‐Catalyzed Allylic C−H Amination of 1,4‐Dienes: A Computational Study

Abstract

Density functional theory calculations have been conducted to investigate the palladium‐catalyzed allylic C−H amination of 1,4‐dienes with commonly available amines. The computations indicate that the reaction begins with the allylic C−H bond cleavage through the concerted proton and two‐electron transfer process to forge the η³‐allyl Pd(II) species. The ensuing C−N bond formation was found to be highly dependent on the basicity of the nucleophile, enabling the regioselectivity switch upon change of the nucleophile. With the weakly basic aromatic amine, the reaction occurs through the hydrogen‐bonding enabled inner‐sphere nucleophilic attack pathway. The distance between the reacting carbon atom and the terminal carbon atom is responsible for the Z/E‐selectivity. The regioselectivity is primarily due to steric repulsion between the allyl group and the ligand. On the other hand, the outer‐sphere nucleophilic attack pathway is favored for the reaction with the more basic aliphatic cyclic amine. The change of the coordinating mode of the allylic moiety was found to play a crucial role in determining the regioselectivity.