Visible Light‐Mediated Coupling of α‐Bromochalcones with Alkenes

Photoredox catalyzed intermolecular couplings of α‐bromochalcones to olefins have been developed. Employing 1 mol% of the iridium complex Ir(ppy) 3 as photocatalyst, vinyl radicals are generated from α‐bromochalcones as the key intermediate, which efficiently engage in a formal [4+2] cyclization with various alkenes. The resulting 3,4‐dihydronaphthalenes can be readily transformed to the corresponding naphthalenes and further cyclized to 5 H ‐benzo[ c ]fluorenes. Alternatively, Heck‐type coupling products are obtained with sterically more hindered alkenes or allylated products if the alkene possesses a suitable leaving group in the allylic position.