Visible Light-Mediated Coupling of α-Bromochalcones with Alkenes

Photoredox catalyzed intermolecular couplings of alpha-bromochalcones to olefins have been developed. Employing 1 mol% of the iridium complex Ir(ppy)(3) as photocatalyst, vinyl radicals are generated from a-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 5H-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.