Synthesis and chemistry of diazo compounds under microwave irradiation: A review

Diazo compounds such as alpha-diazocarbonyls, diazoalkanes, and diazoarenes are well known compounds in organic chemistry. Their synthetic utility is of paramount importance. They are commonly used as precursors of reactive intermediates like ketenes and carbenoids. Their reactions have been traditionally carried out under thermal or photochemical conditions in inert atmosphere. The synthesis and chemistry of such compounds under microwave irradiation have seen steady growth. The present article critically reviews the application of microwave irradiation in synthesis and chemistry of diazoalkanes and alpha-diazocarbonyls. The microwave-assisted reactions via ketenes and carbenes with alcohols, thiols, phenols, amines, imines, alkenes, alkynes, and three-membered heterocyclic compounds, etc. are described. These reactions furnish synthetically useful building blocks and also biologically relevant heterocyclic compounds. Most reactions are accelerated by the use of microwave irradiation. There are also some reports revealing that the reactions did not occur by conventional heating but yielded products on irradiation with microwaves. The mechanisms of the reactions where necessary and synthetic and biological relevance of the products are highlighted.