Recent Progress on Cyclic Nitrenoid Precursors in Transition‐Metal‐Catalyzed Nitrene‐Transfer Reactions

Nitrene‐transfer reactions are powerful synthetic tools for the direct incorporation of nitrogen atoms into organic molecules. The discovery of novel nitrene‐transfer reactions has been dominantly supported not only by improvements in transition‐metal catalysts but also by the employment of novel precursors of nitrenoids. Since pioneering work involving the use of organic azides and iminoiodinanes as practical synthetic tools for nitrogen‐containing compounds was reported, a new approach using various N‐heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene‐transfer chemistry from the viewpoint of its precursors. In particular, the use of N‐heterocycles such as 2H‐azirines, 1,4,2‐dioxazol‐5‐ones, 1,2,4‐oxadiazol‐5‐ones, isoxazol‐5(4H)‐ones, and isoxazoles is comprehensively described, showing the recent remarkable progress in this chemistry. Rings open: This review summarizes transition‐metal‐catalyzed nitrene‐transfer reactions from the viewpoint of the development of nitrenoid species. The use of N‐heterocyclic compounds as novel precursors of nitrenoid species has been significantly broadened in recent years. Various types of ring‐opening and ring‐reconstructing reactions have been achieved.