Et3Al/Light-Promoted Radical-Polar Crossover Reactions of α-Alkoxyacyl Tellurides

Here, we report new radical-polar crossover reactions of alpha-alkoxy carbon radicals for constructing highly oxygenated molecules with contiguous stereocenters. The method employs a 370 nm UV light-emitting diode (LED) for the photoexcitation of alpha-alkoxyacyl telluride, and Et3Al as the radical initiator and terminator. First, Et3Al and UV LED promoted radical coupling between the alpha-alkoxyacyl telluride and cyclopentenone via C-Te bond homolysis, CO expulsion, and C-C bond formation. Second, Et3Al converted the radical species to the corresponding aluminum enolate. Third, the second C-C bond formation occurred via a polar mechanism: intermolecularly with aldehydes/ketones and intramolecularly with epoxide, producing aldol and S(N)2 adducts, respectively. The present coupling reactions increase the molecular complexity in a single step by stereoselective formation of the two hindered C-C bonds. The devised method is expected to be useful for the expeditious assembly of densely oxygenated natural products.