In the presence of palladium(II) acetate [PdA C H T U N G T R E N N U N G (OAc) 2 ] and an N-heterocyclic carbene (NHC) ligand, fluorene derivatives can be generated in good to excellent yields from 2-halo-2'-methylbiaryls through the benzylic C À H bond activation (14 examples; 81-97% yields). The scope and limitations of this protocol have been examined. A wide range of functional groups, such as alkyl, alkoxy, ester, nitrile, and others, is able to tolerate the reaction conditions herein. The cyclization of an isotope-labelled biphenyl gave the corresponding product with a primary kinetic isotope effect (k H /k D = 4.8:1), which indicates that the rate-determining step of this reaction is the activation of the benzylic C À H bond. Moreover, indenofluorenes were also accessed in excellent results from terphenyls (3 examples; 91-92% yields). The cascade reaction of 2,6-dichloro-2'-methylbiphenyl with diphenylacetylene produced 8,9-diphenyl-4H-cyclopentaA C H T U N G T R E N N U N G [def]phenanthrene in 60% yield through the activation of an aryl and a benzylic C À H bond.

Various 1,3-diaryl-2-arylethynyl-1,3-butadienes 7 have been prepared by the Pd-catalyzed trimerization of arylalkynes 4. Their structures and stereochemistry have been confirmed by X-ray crystal analyses. This procedure provides high regioselectivity to generate adducts Z-7 in moderate to excellent yields. The scope, limitations and regioselectivity of this reaction have been investigated. In DMSO at 180 8C, 1,3-di(1-naphthalenyl)-2-