Carbon-nitrogen migration, Curtius

Alkyl-, vinyl-, and aryl-substituted acyl azides undergo thermal 1,2-carbon-to-nitrogen migration with extrusion of dinitrogen — the Curtius rearrangement — producing isocyantes. Reaction of the isocyanate products with nucleophiles, often in situ, provides carbamates, ureas, and other A-acyl derivatives. Alternatively, hydrolysis of the isocyanates leads to primary amines. 

The Hofmatm, Curtius, Schmidt and Lossen rearrangements generally involve nucleophilic migrations from a carbon to an electron deficient nitrogen center (Scheme 5), giving isocyanates as the initial products, which undergo further reactions as already shown in Scheme 2. 

Curtius-type behaviour is followed on irradiation of the azide 610 at 10 K when methoxyisocyanate is obtained by migration of the methoxy group from carbon to nitrogen" . Carbamoyl azide is also photolabile under similar conditions and provides a route to aminonitrene The substituted amide derivative 611 also undergoes conversion to the corresponding isocyanate and, if this is brought about in the presence of carbodiimides, cycloaddition results in the formation of triazoles. ... 

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