Mechanistic Investigation on Rhodium (III)-catalyzed Cycloaddition of 2-vinylphenol Derivatives with Ethyne or Carbon Monoxide by DFT Study

Rhodium-catalyzed cycloaddition reaction was calculated by density functional theory (DFT) M06-2X method to directly synthesize benzoxepine and coumarin derivatives. In this paper, we conducted a computational study of two competitive mechanisms in which the carbon atom of acetylene or carbon monoxide attacked and inserted from two different directions of the six-membered ring reactant to clarify the principle characteristics of this transformation. The calculation result reveal (1) the insertion process of alkyne or carbon monoxide is the key step of the reaction; (2) For the (5 + 2) cycloaddition reaction of acetylene, higher energy is required to break the Rh-O bond of the reactant, and the reaction tends to complete the insertion from the side of the Rh-C bond; (3) For the (5 + 1) cycloaddition of carbon monoxide, both reaction paths have lower activation free energy, and the two will generate a competition mechanism.