Showing papers by "Kenji Itoh published in 2005"

Cp*RuCl-Catalyzed [2 + 2 + 2] Cycloadditions of α,ω-Diynes with Electron-Deficient Carbon−Heteroatom Multiple Bonds Leading to Heterocycles

Abstract: In the presence of a catalytic amount of Cp*RuCl(cod), 1,6-diynes were allowed to react chemo- and regioselectively with electron-deficient nitriles and heterocumulenes at 60−90 °C to afford heterocyclic compounds. The mechanism of the ruthenium-catalyzed regioselective formations of bicyclic pyridines and pyridones were analyzed on the basis of density functional calculations. Cyclocotrimerizations of ethyl propiolate with ethyl cyanoformate or propyl isocyanate gave rise to two of the four possible pyridine or pyridone regioisomers.

Synthesis of 2-Haloalkylpyridines via Cp*RuCl-Catalyzed Cycloaddition of 1,6-Diynes with α-Halonitriles. Unusual Halide Effect in Catalytic Cyclocotrimerization

Abstract: In the presence of 2–5 mol % Cp*RuCl (cod), various 1,6-diynes reacted with α-monohalo- and α,α-dihalonitriles at ambient temperature to afford 2-haloalkylpyridines in 42–93% isolated yields. The failure of acetonitrile, N,N-dimethylaminoacetonitrile, phenylthioacetonitrile, and methyl cyanoacetate as nitrile substrate clearly showed that the α halogen substitution is essential for the present cycloaddition under mild conditions. The cycloaddition of unsymmetrical diynes bearing a substituent on one alkyne terminal gave 2,3,4,6-substituted pyridines exclusively.