Hoffman rearrangement

The Hoffman rearrangement of amides by quaternary ammonium hypochlorites is not particularly efficient under phase-transfer catalytic conditions and only low yields of nitrile, aldehydes, or ketones, which result from oxidation of the amines, are... 

Nitrogen-13 labelled / -phenethylamine [13N]-309 has been synthesized294 by Hoffman rearrangement of [13N]phenylpropionamide, prepared in turn from phenylpropio-nyl chloride and aqueous [13N]ammonia solution (equation 127). 

MethoxyphenyI)-3-carbonyIamino-N-t-butyI-2-oxo-1,2-dihydro-1,8-naphthyridine, (III), was converted into the corresponding 3-urea derivative, (IV), using the Hoffman rearrangement and is described (1,2). The procedure was also performed using 3-carbonylamino-2-oxo-pyridine (3). 

Whilst the mechanism has not been proven, it is proposed that this rearrangement is similar to Hoffman rearrangement reactions, which occur with quaternary ammonium compounds containing P C-H bonds [16]. With the peralkylated polyaminophosphonium hydroxides, this rearrangement reaction occurs readily at room temperature, suggesting that in these molecules nitrogen has sufficient electropositive character to facilitate the rearrangement reaction. 

PET wastes can be converted via ammonolysis to paraphenylenediamine, which is a basic raw material for the high-modulus-fiber Kevlar or for high-value hair dyes. The chemical basis for this process is a modified Hoffman rearrangement. The synthesis may be done via the following three stages [33] ... 

The use of azides in the Curtius reaction is hazardous and the utility of the Hoffman and Lossen rearrangements is limited to preparation of aliphatic isocyanates, as aqueous media are employed (aromatic isocyanates react readily with water to form substituted ureas). Tertiary butyl hypochlorite can be used for non-aqueous Hoffman rearrangements but is costly. In practice mostly phosgenation of a primary amine is commercially important ... 

Keywords Alkyl-shift Hoffman rearrangement Polycyclization and iodonio-Claisen Prins-Pinacol Ring expansions and cmitractions Transposition... 

Chemoselective reduction with NaBH4 followed by tert-butyldiphenylsilyl (TBDPS) protection provided the protected diol 106 in ca. 40% yield over four steps. Then, Parkins hydration of the nitrile moiety followed by reduction of the azide afforded the amido Boc-amine 107, which finally underwent Hoffman rearrangement to yield the key intermediate 108 as a single diastereomer in ca. 15% overall yield (nine steps) with 92% ee. 

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