Nitrenes generated from nitro-compounds by various phosphorus reagents in heterocyclic synthesis. A convenient route to substituted 3H-azepines

Reductions of substituted nitrobenzenes with various trivalent phosphorus reagents in the presence of an excess of primary or secondary amine lead to substituted azepines by addition to the nitrene intermediate followed by ring expansion. Azepines substituted with functional groups are thus readily available for further synthesis. Where ring expansion does not occur, typical nitrene reactions such as proton abstraction from the amine solvent, insertion into the N–H bond, and trapping by the phosphorus reagent are observed.