Photochemical Ring Opening of Cyclopropyl Silyl Ethers Enables β–β Coupling, Radical‐Polar Crossover and Annulation

A photochemical radical ring opening strategy is reported in which cyclopropyl silyl ethers undergo single-electron oxidation and fragmentation under visible-light photoredox conditions to furnish β-carbonyl radicals. These intermediates engage electron-deficient alkenes in a controlled intermolecular addition process that combines radical ring opening with C-C bond formation. The reaction delivers β-β coupling products across a broad substrate scope, including simple and complex alkenes and substrates that undergo regioselective 1,6-addition. The resulting adducts can be further advanced through downstream annulation chemistry, whereas under modified conditions, the same intermediates can undergo radical-polar crossover and subsequent aldol cyclization, enabling access to three separate product classes from a common cyclopropyl precursor. The synthetic utility of the method is demonstrated through divergent entry into the carbocyclic frameworks of the kaurene and phyllocladane natural product families and the first total synthesis of (-)-ent-melicodenone C.