Chapter 5: Migration to Electron-Deficient Nitrogen

The chapter provides detailed mechanistic analysis of four major rearrangement families: the Hofmann rearrangement of primary amides, the Curtius rearrangement of acyl azides, the Lossen rearrangement of hydroxamic acid derivatives, and the Schmidt rearrangement involving carboxylic acids and hydrazoic acid. Each transformation generates reactive isocyanate intermediates that serve as key synthetic intermediates, subsequently undergoing hydrolysis to afford primary amines or reaction with nucleophiles to produce ureas and carbamates. The chapter emphasizes that these rearrangements proceed through either concerted mechanisms or stepwise pathways involving nitrene and acyl-nitrene intermediates, with the mechanism choice influencing migratory selectivity and reaction outcomes. Particular attention is devoted to synthetic applications including the preparation of amines and protected amino derivatives from carboxylic acid precursors, ring expansion strategies in lactam chemistry, and the construction of nitrogen-containing heterocycles relevant to natural product synthesis. The material demonstrates how understanding migratory group selectivity and intermediate reactivity enables chemists to design transformations for complex molecular framework modifications.