Isotope Effects and the Mechanism of Photoredox-Promoted [2 + 2] Cycloadditions of Enones.

ABSTRACT: 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 C_β-C_β 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 C_β-C_β 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 com

SUBMITTER: Kuan KY 

PROVIDER: S-EPMC8522857 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature