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

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.