Tris(benzocyclobutadieno)triphenylene and Its Lower Biphenylene Homologues by Palladium-Catalyzed Cyclizations of 2,3-Didehydrobiphenylene

The Pd-catalyzed cycloaddition of didehydrobiphenylenes 2a,b, generated from the corresponding 3-(trimethylsilyl)-2-biphenylenyl triflates with fluoride, furnishes the C₃-symmetric trimers 1a,b in which the embedded triphenylene unit is distorted to increase the aromaticity of the central benzene ring. Cocylization of 2a,b with dimethyl acetylenedicarboxylate provides the phenanthrene- and naphthalenecarboxylic ester analogues, depending on the catalyst used.