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26.6.8.1.1 Method 1: Neber Rearrangement

DOI: 10.1055/sos-SD-026-00761

Suffert, J.Science of Synthesis, (200526954.

The Neber rearrangement was discovered in 1926; it originally utilized O-tosyl oximes of benzyl ketones 265 (R1=aryl; R2=alkyl or aryl).[‌223‌‌228‌] The probable mechanism involves the loss of 4-toluenesulfonic acid, mediated by deprotonation at the benzylic position, forming a nitrene and then an azirine.[‌229‌] Such azirines when refluxed in propan-2-ol with a catalytic amount of base give the isopropoxylated aziridines 266 in high yield. Azeotropic distillation of the aziridines in toluene, and acidic hydrolysis with hydrochlo­ric acid, affords amino ketones as the hydrochloride salts 267 (Scheme 120). When there are two potential sites for deprotonation, the direction taken favors the migration of the more electrophilic carbon atom to the nitrogen atom.[‌225‌]

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