53. Activation versus Ring Opening and Inner- versus Outer-Sphere Concerted Metalation-Deprotonation in Rh(III)-Catalyzed Oxidative Coupling of Oxime Ether and Cyclopropanol: A Density Functional Theory Study

Meng, R.; Bi, S.;* Jiang, Y.-Y.; Liu, Y. C-H. J. Org. Chem. 2019, 84, 11150-11160. Download Link

Abstract: The Rh(III)-catalyzed oxidative coupling of oxime ether (S1) and cyclopropanol (S2) with Cu(II) as the oxidant features the combination of C−H activation and strained ring opening. The sequential order of C−H activation versus ring opening was investigated with the aid of density functional theory calculations. Prior ring opening due to the release of ring strain is found to be favored over the prior C−H activation. For the prior ring-opening mechanisms, the outer-sphere concerted metalation− deprotonation (CMD) mechanism in C−H bond activation is energetically favored. The outer-sphere CMD mechanism proposed in this work favors solvent effects and affords the N→Rh binding that allows a directing role of the Schiff base group. In conclusion, the reaction was suggested to undergo prior ring opening followed by C−H activation via the outer-sphere CMD mechanism.