Benzamide

Inorg Chem. 2015 Apr 20;54(8):3958-69.

Density functional theory study of Rh(III)-catalyzed C-H activations and intermolecular annulations between benzamide derivatives and allenes.[Pubmed: 25856513]

METHODS AND RESULTS:
Density functional theory has been applied to gain insight into the Cp*Rh(OAc)2-catalyzed C-H activation and intermolecular annulation of Benzamide derivatives with allenes. The study shows that the reactions proceed in three steps: (1) C-H activation induced by Rh catalyst reacting with Benzamide derivatives, (2) carborhodation of allene, and (3) regeneration of Rh catalyst. The results indicate that the N-H deprotonation makes the following C-H activation much easier. The regio- and stereoselectivities of 1a (N-pivaloyloxy Benzamide)/2a (cyclohexylallene) and 1b (N-pivaloyloxy-4-methyl-Benzamide)/2b (1,1-dimethyl allene) depend on the allene carborhodation step. The steric hindrance effect is the dominant factor. We also discuss the reaction mechanism of 1c (N-methoxy Benzamide)/2a.
CONCLUSIONS:
The chemoselectivity between 1c/2a is determined by the N-O cleavage step. Replacement of OPiv by OMe leads to loss of the stabilization effect provided by C=O in OPiv. Additionally, Cp*Rh(OAc)(OPiv) is produced in the Cp*Rh(OAc)2 regeneration step, which can work as catalyst as well.