Efficient Generation of Pyridines by Ruthenium Carbene Mediated [2+2+2] Cyclotrimerization

Hoveyda-Grubbs' catalyst is able to catalyze crossed [2 + 2 + 2] cyclotrimerizations of diynes with nitriles. Pyridines are obtained with excellent yields when using activated nitriles and low to moderate yields with nonactivated nitriles which are unreactive under previously described ruthenium catalyzed reaction conditions. Both terminal and internal alkynes give the reaction using this experimental procedure.