54120-34-2Relevant academic research and scientific papers
Isotope Effects and the Mechanism of Photoredox-Promoted [2 + 2] Cycloadditions of Enones
Kuan, Kai-Yuan,Singleton, Daniel A.
, p. 6305 - 6313 (2021/05/29)
13C kinetic isotope effects (KIEs) for the photoredox-promoted [2 + 2] cycloaddition of enones were determined in homocoupling and heterocoupling examples. The only significant KIEs were observed at the β carbon, indicating that Cβ-Cβ bond formation is irreversible. However, these KIEs were much lower than computational predictions, suggesting that product selectivity is determined in part by a step prior to Cβ-Cβ bond formation. The results are explained as arising from a competition between C-C bond formation and electron exchange between substrate alkenes. This idea is supported by a relatively small substituent effect on substrate selectivity. The possible rates for electron transfer and bond-forming steps are analyzed, and the competition appears plausible, particularly if the mechanism involves a complex between reduced and neutral enone molecules.
