Vinyl Azides as Versatile Synthons for the Synthesis of Nitrogen-containing Heterocycles

Vinyl azides have emerged as important synthons in recent years and a variety of |useful synthetic methodologies have been achieved in the construction of the nitrogen heterocycles, such as indoles, pyrroles, imidazoles, pyrazoles, pyridines and pyrimidines. The unstable azide group and the presence of neighboring unsaturated double bond accentuate the high reactive ity of vinyl azides with other electrophiles and nucleophiles in various manners. One of the important features of vinyl azides is that they can decompose to vinyl nitrenes or highly strained three-membered cyclic imines, 2H-azirines. These two three-atom intermediates can easily undergo tandem reactions with 1,3-dipoles to generate the nitrogen-containing heterocycles. Vinyl azide can also act as a two-atom synthon while azide group serves as a leaving group in the cycloaddition reactions. What's more, when vinyl azide is connected with a carbonyl group in the α-position of azide, the resulted α-azidovinylketone can react with the dinucleophiles, leading to the amino substituted ring. The purpose of this review is to present the synthetic approaches achieved both in our group and other groups. Keywords: 2H-azirine, nitrene, nitrogen heterocycles, synthon, vinyl azides, α-azidovinylketone.