Radical alkylation and formylation of vinyl epoxides

Abstract

Photo-mediated intermolecular radical alkylations and formylations of vinyl epoxides have been studied. Vinyl epoxides were prepared from the corresponding keto epoxides. Intermolecular radical reactions of vinyl epoxides using n-$Bu_3SnH$/AIBN system could not be carried out satisfyingly because of the very high radical scavenging power of the tin hydride (k$\sim10^{-6}M^{-1}s^{-1}$). But selective homolytic cleavage of $Bu_6Sn_2$ to generate tin radical in the absence of any efficient radical scavenger like n-$Bu_3SnH$ was well performed under mild irradiation using photosensitizer such as a acetone. Using photo-mediated tin radical generation method, the intermolecular radical alkylations of endocyclic vinyl epoxide with alkyl iodides were performed and afforded alkylated products in moderate yields. Also, the intermolecular radical formylations of vinyl epoxides with 1,3-dioxolane, formyl group synthon, were achieved in good yields. However, relatively poor yields were obtained from the alkylations and formylations of vinyl epoxides, which could undergo 1,5-H atom or 1,5-Sn group transfer.