2-Arylbenzoyl chlorides undergo annulative coupling with internal alkynes in the presence of a catalyst system of [IrCl(cod)]2/P(t-Bu)3 to selectively afford the corresponding phenanthrene derivatives accompanied by elimination of carbon monoxide and hydrogen chloride. The reaction occurs without addition of any external base. Deuterium-labeling experiments using 2-(d5-phenyl)benzoyl chloride suggest that the rate-determining step does not involve the C2'-H bond cleavage. Formation of a [(t-Bu)3PH][(biphenyl-2,2'-diyl)Ir(CO)Cl2] complex dimer, of which the structure was determined by single-crystal X-ray analysis, from a stoichiometric reaction at 60 °C without addition of alkyne also supports the facile C-H cleavage.

A rhodium-catalyzed annulative coupling of (2-arylphenyl)boronic acids with alkynes has been developed for the facile construction of phenanthrene frameworks. The reaction proceeded without external bases, and dioxygen worked as a terminal oxidant. Deuterium-labeling experiments indicated the involvement of fivemembered rhodacycle intermediates.

A series of substituted [4] and [5]helicenes were synthesized in moderate to good yields by an Ir-catalyzed annulative coupling of biarylcarboxylic acid chlorides with internal alkynes, which involves facile C-H bond cleavage and decarbonylation. The double annulative coupling of 1,1′:5′,1′′-ternaphthalene-2,2′′-dicarboxylic acid dichloride with 4-octyne was also accomplished to give rise to an S-shaped double helicene. Unexpectedly, a π-extended benzofluoranthene-merged [5]helicene was constructed through the annulative coupling and the successive C(aryl)-C(aryl) bond forming reaction when 1,1′:4′,1′′-ternaphthalene-2,2′′-dicarboxylic acid dichloride was employed as the substrate. The crystal structure and the optical properties of the latter unique product were also investigated.

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The catalyst system which includes an iridium complex is highly efficient for a selective formation of phenanthrene structures.