Metal-catalyzed Heterocyclization: Synthesis of five- and six-membered Nitrogen Heterocycles Through Carbon-Nitrogen Bond Forming Reactions

Nitrogen heterocycles are widespread in nature and their applications in bioactive pharmaceuticals, agrochemicals and functional materials are well known. A number of protocols have been developed for their syntheses. This review article covers an updated (published during 2005-2008) summary of transition metal-catalyzed approaches for the syntheses of five- and six-membered ring heterocycles with one nitrogen atom via carbon-nitrogen bond forming reactions. The syntheses of five-membered ring heterocycles include pyrroles, pyrrolidines, indoles, oxindoles, isoindoles, indolizines and carbazoles. The syntheses of six-membered nitrogen heterocycles covered are pyridines, piperidines, quinolines and isoquinolines. In some cases, mechanistic rationalizations for the formation of the heterocycles have also been discussed.