DFT study on the organocatalytic carbonyl–olefin metathesis

Organocatalytic carbonyl–olefin metathesis has been given a systematic theoretical study with density functional theory (DFT) method. The catalytic cycle includes three key steps: (a) (3 + 2) cycloaddition of (E/Z)-hydrazonium ion I (from the reaction of aldehyde with the hydrazine catalyst) with olefin to produce pyrazolidinium ion II; (b) proton transfer between two nitrogen atoms in II to give pyrazolidinium ion III; (c) cycloreversion of III to produce hydrazonium ion IV, whose hydrolysis leads to the metathesis product. It is found that the stereo-selectivity of product is determined by the first step. The catalyst with high steric effect can effectively improve the stereo-selectivity. The second step, namely the proton transfer, is the rate-determining step in the whole catalytic cycle. Water molecule can effectively facilitate this step. In the third step, olefins with high strain, such as cyclopropene substrate, favor the cycloreversion.