Ruthenium-Catalyzed Cycloaddition of 1,6-Diynes and Nitriles under Mild Conditions: Role of the Coordinating Group of Nitriles

Abstract
In the presence of a catalytic amount of [Cp*RuCl(cod)] (Cp*=pentamethylcyclopentadienyl, cod=1,5-cyclooctadiene), 1,6-diynes were allowed to react chemo- and regioselectively with nitriles bearing a coordinating group, such as dicyanides or α-halonitriles, at ambient temperature to afford bicyclic pyridines. Careful screening of nitrile components revealed that a CC triple bond or heteroatom substituents, such as methoxy and methylthio groups, proved to act as the coordinating groups, whereas CC or CO double bonds and amino groups failed to promote cycloaddition. This suggests that coordinating groups with multiple π-bonds or lone pairs are essential for the nitrile components.