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Advances in C-H activation by palladium: migration and cyclocarbonylation

Palladium-catalyzed intramolecular C-H activation of o-halobiaryls has been used to carry out important chemical transformations. For instance, in the presence of catalytic amounts of Pd(0), o-halobiaryls are readily cyclocarbonylated under an atmosphere of CO to produce fluorenones in high yields with good regioselectivity. This methodology has been successfully applied to the preparation of polycyclic fluorenones and fluorenones containing fused isoquinoline, indole, pyrrole, thiophene, benzothiophene, and benzofuran rings. A novel 1,4-Pd migration between the oand o'-positions of biaryls has been observed in organopalladium intermediates derived from o-halobiaryls. The organopalladium intermediates generated by this unique C-H activation-migration process have been trapped by way of a Heck reaction and Suzuki-Miyaura cross-coupling with arylboronic acids. Similarly, organopalladium intermediates generated by 1,4-Pd migration have been trapped by intramolecular arylation to produce fused polycycles. This unique migration-arylation methodology have been used to prepare complex polycyclic compounds containing fused benzofuran, quinoline, oxepine, indole, phenanthrene, and naphthalene rings.