Mechanism of the Rhodium‐Catalyzed Asymmetric Isomerization of Allylamines to Enamines

A theoretical study of the mechanism of the rhodium‐catalyzed asymmetric isomerization of allylamines to enamines by using density functional theory with the B3LYP functional leads us to discard the so far accepted nitrogen‐triggered mechanism, in which the isomerization occurs on N‐bonded intermediates and transition states, in favor of a variation of the classical allylic mechanism for olefin isomerization. The modified allylic mechanism consists of four main steps: 1) N‐coordination of the allylamine to Rh I ; 2) intramolecular isomerization from κ 1 ‐(N)‐coordination to η 2 ‐(C,C)‐coordination of the allylamine; 3) oxidative addition of C 1 H to form a distorted octahedral η 3 ‐allyl complex of Rh III ; and 4) hydrogen transfer to C 3 (reductive C 3 H elimination). The two hydrogen transfer steps (oxidative addition and reductive elimination) have the highest barriers of the overall process. The oxidative addition barrier, which includes solvent effects, is 28.4 kcal mol −1 . For the reductive elimination, the value in solvent is 28.6 kcal mol −1 , very similar to the oxidative addition barrier.