Rhodium-Catalyzed Synthesis of Indolizines and Imidazopyridines

Significance

A Rh-catalyzed synthesis of indol­izines and imidazopyridines is described which involves an interesting reaction of alkynes and nitriles with pyridotriazoles with overall loss of nitrogen. A proposed mechanism involves the initial equilibration of the closed 1 and open 2 isomers of the pyridotriazole, followed by formation of the Rh-carbenoid species 3 and direct nucleophilic attack of an alkyne or nitrile to finally afford the indolizine and imidazopyridine derivatives. C7-substitution in the pyridotriazoles is required to drive the equilibrium to the open-ring form 2.