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 M06-2X method to directly synthesize benzoxepine and coumarin derivatives. In this work, 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 results reveal that: (ⅰ) the insertion process of alkyne or carbon monoxide is the key step of the reaction; (ⅱ) 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; (ⅲ) for the (5+1) cycloaddition of carbon monoxide, both reaction paths have lower activation free energy, and the two will generate a competition mechanism