Reduction of Nitro and Nitrosoarenes

Most commonly, deoxygenation is effected with tervalent phosphorus reagents such as (EtO)jP, PhjP, (EtO)2PMe, and others. Whether 3 or a discrete nitrene is the reactive species still remains in doubt. Evidence in favor of a nitrene comes from the very similar yields of products obtained from the deoxygenation of nitroaromatics and thermolysis of corresponding aryl azides. On the other hand, a kinetic analysis and a labeling study in other systems come 

it is apparent that generalizations about nitrene involvement in deox ygenations, or any other reaction discussed in this section, cannot be made from studies of any one system, and ultimately each case must be treated on its merit. Where in this review nitrene intermediacy is postulated for reactions by analogy to other processes this point should be borne in mind. 

Recently, tributylphosphine has been found to be a most efficient deox-ygenating agent permitting the conversion of nitrobenzene in alcoholic solution to 2-alkoxy-3/f-azepines in 60% yield  

Deoxygenations have been carried out with other than phosphorus reagents. Phenazine is formed on cyclization of 2-nitrodiphenylamine in the presence of ferrous oxalate in the Waterman-Vivian synthesis but a metal-nitrene complex (a nitrenoid) is thought to be involved rather than a true nitrene  

Treatment of 2-nitrobiphenyl with hexamethyldisilane at 240°C gives carbazole, providing a new method of generating nitrenes from nitro compounds. 

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