Dioxazolones: Stable Substrates for the Catalytic Transfer of Acyl Nitrenes

Dioxazolones are a convenient class of acyl nitrene transfer reagents. Their application in homogeneous transition-metal catalysis has led to many new amidation reactions. Dioxazolones are typically activated by transition metals at relatively low reaction temperatures. The metal nitrenoids formed by decarboxylative activation of dioxazolones are generally electron deficient and commonly react in a concerted fashion. “Intermolecular” nitrene insertion reactions involving preactivated C–H bonds (“inner-sphere” mechanism) easily compete with the Curtius-type rearrangement, but for intramolecular “direct” nitrene transfer/insertion reactions involving nonpreactivated substrates (i.e., without preceding formation of metal–carbon or metal–hydride bonds) extensive ligand optimization is important to prevent such unwanted side reactions. The ease of dioxazolone synthesis, formation of CO₂ gas as the sole byproduct from reactions with dioxazolones, and the importance of nitrene transfer reactions in general has led to the development of several interesting reactions producing N-aryl amides, oxazoles, and lactams. Since the activation of dioxazolones proceeds under mild reaction conditions, stereo- and enantioselective reactions are also possible, which is useful for the synthesis of bioactive nitrogen-containing compounds. This review provides an overview of these reactions reported in recent years.