No abstract

[reaction: see text] [Ir(cod)Cl]2/DPPE was found to be a new catalyst for the cycloaddition of alpha,omega-diynes with monoynes to give polysubstituted benzene derivatives in high yields. Internal monoynes as well as terminal monoynes could be used. The reaction tolerates a broad range of functional groups such as alcohol, amine, alkene, ether, halogen, and nitrile. The reaction of 1,6-octadiyne derivatives with 1-alkynes gives ortho products and meta products. The regioselectivity could be controlled by the choice of ligand. The reaction with DPPE was meta selective, with meta selectivity of up to 82%. The reaction with DPPF was ortho selective, with ortho selectivity of up to 88%. We propose a mechanism to account for this regioselective cycloaddition. [Ir(cod)Cl](2)/DPPE also catalyzed the cycloaddition of alpha,omega-diynes with 2,5-dihydrofuran to give bicyclic cyclohexadiene derivatives. The reaction with 2,3-dihydrofuran and n-butyl vinyl ether gave benzene derivatives instead of cyclohexadiene derivatives. We also propose a mechanism to account for this novel aromatization that includes cleavage of the C-O bond.

Cycloaddition reactions O 0070Iridium Complex-Catalyzed [2 + 2 + 2] Cycloaddition of α,ω-Diynes with Monoynes and Monoenes. -A detailed account on the recently published Ir-catalyzed cycloaddition of diynes with monoalkynes is presented and extended by monoalkenes as addition partners. In some of the reactions using monoalkenes, a novel aromatization of initial formed cyclohexadiene derivatives is observed. A ligand-controlled switch in regioselectivity is discovered in the reactions of 1,6-octadiene derivative (XII) with terminal alkynes. -(KEZUKA, S.; TANAKA, S.; OHE, T.; NAKAYA, Y.; TAKEUCHI*, R.; J. Org. Chem. 71 (2006) 2, 543-552; Dep. Chem. Biol. Sci., Aoyama Gakuin Univ., Sagamihara 229, Japan; Eng.) -Nuesgen 23-028