Named rearrangements Hofmann

Degradation reactions of carboxylic acids and their derivatives to amines and their derivatives with one less carbon unit involve rearrangements of a carbon to an electron deficient nitrogen atom as key steps, namely the Hofmann Curtius (C), - Schmidt and Lessen rearrangements, as... 

Electrolysis of amides in MeOH containing the bromide ion efficiently led to products of the Hofmann rearrangement (for example, 119 to 120 Scheme 43) [131]. This reaction, named the electrochemically induced (E-I) Hofmann rearrangement, is achieved without any bromine and base under mild and neutral reaction conditions. 

Into this group fall the named oxidation rearrangement reactions which proceed with carbon-carbon bond cleavage and 1,2-transfer of an alkyl group to a heteroatom, such as the Baeyer-Villiger reaction (discussed in Chapter 5.1, this volume) and the Beckmann reaction (found in Chapter 5.2, this volume) of ketones, as well as the Hofmann reaction/Schmidt reaction/Curtius reanangement of carboxylic acid derivatives. The two examples discussed here involve related reactions of alcohols. 

The rearrangement has a mechanism similar to those of the Hofmann rearrangement of amides, the Lossen rearrangement of acylhydroxamic esters, the Schmidt rearrangement of carbonyl compounds and the Wolff rearrangement of diazoketones. Evidence concerning the mechanism of one can often be applied to the others, and the whole family has been reviewed briefly . Sometimes the distinction is made that the conversion of an acyl azide into an isocyanate or urethane is the Curtius rearrangement whereas the overall sequence is the Curtius reaction, but usually the former name is used for both processes. 

Despite its mechanistic complexity, the Hofmann rearrangement often gives high yields of both aryl- and alkylamines. For example, the appetite-suppressant drug phentermine is prepared commercially by Hofmann rearrangement of a primary amide. Commonly known by the name /cn-phen, the combination of phentermine with another appetite-suppressant, fenfluramine, is suspected of causing heart damage. 

Types of reactions such as Fridel-Crafts, Grignard, Meerwin-Ponndorf, Cannizzaro, Clemenson. Wolff-Kishner, Hofmann Degradation, Beckman Rearrangement, Simmons-Smith, Piels-Alder, Wurtz-Fitig, etc. may not be household names to everyone, but they are to many organic chemists. More importantly, literature sources can be searched for these classifications to give an overall perspective to a reaction under study. 

In summary, the Hofmann Rearrangement presents the synthetic chemist with a rich selection of possible options depending on the system at hand, something that most name reactions do not offer. 

In this section we have explored a number of rearrangement reactions that involve ketenes or ketene-like intermediates. Notice that each of these rearrangements is a name reaction (Wolff, Arndt-Eistert, Hofmann, and Curtius). Don t panic about keeping the specifics of the reactions connected to the names. Most instructors will not ask you to reproduce the reactions by name. However, if your future includes organic chemistry, you wiU see them again and become familiar with them. Of course if your future does not include organic chemistry, at least you can appreciate the predictability and trends these reactions illustrate. 

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