A Domino Palladium-Catalyzed C-C and C-O Bonds Formation via Dual O-H Bond Activation: Synthesis of 6, 6-Dialkyl-6H-benzo[c]chromenes

An efficient Pd-catalyzed domino reaction of alpha,alpha-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, beta-carbon cleavage, and finally intramolecular Buchwald-Hartwig cyclization. This domino process effectively involves breaking of five sigma-bonds (2C-Br, 2O-H, and a C-C) and formation of two new sigma-bonds (C-C and C-O). This mechanistic pathway is unprecedented and further illustrates the power of transition metal catalysis.