Developments in Arylnitrene Chemistry: Syntheses and Mechanisms New synthetic methods (31)

Abstract Aryl‐ and heteroaryl‐nitrenes can take part in intra‐and intermolecular reactions in both of their possible electronic states (triplet and singlet). In this review we have endeavored to high‐light recent synthetic uses of these reactive intermediates as well as draw attention to avenues open to further exploration in this field. Singlet arylnitrenes will interact with suitable ortho ‐positioned substituents to give a variety of fused azoles, some in excellent yield. In suitable solvents and in presence of amines and alcohols, phenylnitrenes undergo ring expansion to azepines which can also occur in nitrenes of certain fused bicyclic aromatics (naphthalene, quinoline, isoquinoline, benzo b thiophene). The latter nitrenes may also give rise to o ‐diamines which are useful starters for further heterocyclic synthesis. Triplet arylnitrenes (usually regarded as having only a nuisance effect in synthetic work) may also be utilized in practicable heterocyclic syntheses within a suitable molecular framework. Decomposition of aryl azides in a mixture of an organic and polyphosphoric acid leads to fused oxazoles. The mechanism is discussed for all the reactions considered.