Cyclotrimerization reactions of arynes and strained cycloalkynes



The use of arynes and related species as substrates in metal-catalyzed cycloaddition reactions leads to structurally interesting products. Palladium-catalyzed cyclotrimerization of arynes provides a new method for the synthesis of polycyclic aromatic hydrocarbons. For instance, the chemoselective formal [2 + 2 + 2] cocycloaddition of 2,3-triphenylynes with alkynes affords extended triphenylenes, which are good candidates to behave as liquid crystals. Cotrimerization of benzyne and electron-deficient alkenes selectively affords dihydrophenanthrenes or ortho-olefinated biaryls depending on the catalytic system employed. The use of 2,2′-bis(diphenylphosphino)-1,1′-binophythyl (BINAP)-based palladium(0) catalysts in the cocyclotrimerization of 7-methoxynaphthalyne and dimethyl acetylenedicarboxylate affords an enantiomerically enriched tetrasubstituted pentahelicene, the first example of a metal-catalyzed enantioselective reaction involving arynes. Strained cyclic alkynes can also participate in the palladium-catalyzed cyclotrimerization reactions, which again lead to structurally interesting products. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 326–333; 2007: Published online in Wiley InterScience ( DOI 10.1002/tcr.20132