The Bestmann-Ohira Reagent and Related Diazo Compounds for the Synthesis of Azaheterocycles

Azaheterocycles are one of the most prevalent classes of compounds present in numerous bioactive compounds, natural products, and agrochemicals, and undoubtedly, new methods to access them are always in high demand. Among the methods available, the 1,3-dipolar cycloaddition reactions involving diazo compounds are particularly attractive because of their ability to rapidly construct densely functionalized azaheterocycles in a regioselective manner. In this context, the Bestmann-Ohira reagent has become a well-known reagent for the 1,3-dipolar cycloaddition reactions to produce phosphonylated heterocycles, besides its widespread use as a homologating agent for the conversion of aldehydes to alkynes. This account details our efforts toward broadening the synthetic utility of the Bestmann-Ohira reagent and related compounds for the preparation of azaheterocycles such as pyrazoles, spirooxindoles, triazoles, triazolines, and spiropyrazolines, emphasizing on domino multicomponent reactions employing readily available feedstock reagents.