A Ruthenium Complex-Catalyzed Cyclotrimerization of Halodiynes with Nitriles. Synthesis of 2-and 3-Halopyridines

Monohalo- and dihalodiynes efficiently undergo [2+2+2]cyclotrimerization with nitriles in the presence of a catalytic amount of the ruthenium complex Cp*RuCl(cod) (10mol%) to afford the corresponding halopyridines under ambient conditions in good isolated yields (up to 90%). The halopyridines are formed as two separable regioisomers. This is the first example of a direct synthesis of halopyridines from haloalkynes and nitriles.