A decade of advances in the reaction of nitrogen sources and alkynes for the synthesis of triazoles

The cyclization reactions of alkynes have become one of the most important and useful methodologies for the preparation of heterocycles. To this end, the association between alkynes and nitrogen sources are versatile substrates for the synthesis of triazole derivatives. The improvement in the synthesis of triazoles by the use of copper catalysts in cycloaddition reactions, as well as the significant advances obtained with the use of other transition metals, such as gold, iridium, iron, nickel, ruthenium, samarium, silver, and zinc, to promote the cyclization of alkynes and nitrogen sources are addressed in this review. Furthermore, there has been a significant interest in recent years in developing simple, clean, non-toxic, cost-effective and eco-friendly protocols. In this sense, the reaction of alkynes with nitrogen sources, in the complete absence of transition metals, reaches many of these requirements becoming a good alternative to the synthesis of triazoles. For this reason, the last topic of this review deals with the synthesis of triazoles using alkynes and nitrogen sources under transition metal-free conditions.