DFT calculations were performed on several systems utilizing a rhodium-carbenoid intermediate to perform C-H insertion reactions, affording β- and γ-lactones. While previous computational studies have proposed a simple one-step insertion mechanism to account for observed formation of <i>both</i> of these products, new computational evidence suggests that this mechanism might only be consistently valid for the formation of γ-lactones. The formation of β-lactones can proceed <i>via</i> two possible mechanisms depending on the substituents flanking the carbenoid. While some substituents appear to promote the one-step insertion mechanism, others are able to stabilize a novel two-step mechanism involving a nominal retro-ene rearrangement and subsequent ketene/carbonyl [2+2] cycloaddition. This finding could have significant implications for experimental work in the stereo-control of Rh-catalyzed syntheses of lactones.

DFT studies of unique mechanistic differences in the Rh-catalyzed synthesis of β- and γ-lactones

251st National Meeting (2016)

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