Azides may be converted to amines by hydrogenation, but another possibility is the Staudinger Reaction, which is a very mild azide reduction. As there are a variety of methods for preparing azides readily, the Staudinger Reaction makes it possible to use -N3 as an -NH2 synthon.
Mechanism of the Staudinger Reaction
Triphenylphosphine reacts with the azide to generate a phosphazide, which loses N2 to form an iminophosphorane. Aqueous work up leads to the amine and the very stable phosphine oxide.
2,2′-Dipyridyl diselenide catalyzes a direct reaction of carboxylic acids with azides and trimethylphosphine at room temperature. The mechanism of the process, which is not an aza-Wittig reaction, has been elucidated.
J. Burés, M. Martín, F. Urpí, J. Vilarrasa, J. Org. Chem., 2009, 74, 2203-2206.
One-Pot Synthesis of Polysubstituted Imidazoles via Sequential Staudinger/aza-Wittig/Ag(I)-Catalyzed Cyclization/Isomerization
J. Xiong, X. Wei, Z.-M. Liu, M.-W. Ding, J. Org. Chem., 2017, 82, 13735-13739.