Quaternary ammonium salts, Sommelet-Hauser rearrangement

Rearrangement of benzylic quaternary ammonium salts (Sommelet-Hauser)... 

Benzylic quaternary ammonium salts, when treated with alkali metal amides, undergo a rearrangement called the Sommelet-Hauser rearrangementSince the product is a benzylic tertiary amine, it can be further alkylated and the product again subjected to the rearrangement. This process can be continued around the ring until an ortho position is blocked. ... 

Fluoride ion-assisted desilylation has been extensively used to create an ylid from a /V-silyl methyl-quaternary ammonium salt. Its evolution to final produces) is variable and Sommelet-Hauser and Stevens rearrangement products were obtained (often as major products) in a ratio that can be shifted from one structure to another very close one, as in examples 1 and 2 dealing with //-benzyl salts.246,366 Differences in the solvents used are not significant because in the first example, HMPA does not reverse the ratio, yields and selectivity being just a bit lower, /so-toluene was proposed as an intermediate in example 1 it might also be the intermediate in example 2. Thus product partition reflects the relative ability of the C-H or the C-C bonds to be cleaved to produce aromatization with proton or a-amine carbocation migration. 

Sommelet-Hauser rearrangement The rearrangement of a benzyl quaternary ammonium salt, C6H5CH2N+R3X-, when treated with an alkali metal amide to give the orthomethylbenzyl tertiary amine, o-CH3C6H4CH2NR2. The tertiary amine may subsequently be alkylated, and the reaction... 

Sommelet-Hauser rearrangement. Rearrangement of benzyl quaternary ammonium salts to orr/to-substituted benzyldialkylamines on treatment with alkali metal amides. 

In the presence of NaNH2 benzylic quaternary ammonium salts generally lead to the Sommelet-Hauser rearrangement (refs. 90, 92-104). An ortho alkylation takes place via an exomethylene intermediate. If the two ortho and ortho positions are methylated, the methylene compounds can be isolated (refs. 92, 93). The first anion formed in this reaction can be trapped at a very low temperature (-80 °C) in an aldol reaction for example (ref. 103). At -30°C the isomerization and the rearrangement occur (Fig. 16). 

In the Sommelet—Hauser rearrangement, a benzyl quaternary ammonium salt reacts with a strong base to give a benzyl tertiary amine, as exemplified below ... 

The mechanism of the [2,3]-migration in a quaternary ammonium salt when treated with strong bases in the classic Sommelet-Hauser rearrangement is well studied, usually in contrast with the related [1,2]-migration observed in the same systems as a consequence of the Stevens rearrangement. Its mechanism was easily clarified by intermediate isolation and labeling experiments. ... 

The transformation of quaternary ammonium salts 1 and sulfonium salts 3 to the corresponding amines 2 and sulfides 4 in the presence of a strong base is known as Stevens rearrangement. The salts are usually obtained by the alkylation of the corresponding amines and sulfides. The competing reaction is the Sommelet-Hauser rearrangement. 

Sigmatropic rearrangements of benzyl quaternary ammonium salts are known as the Sommelet-Hauser rearrangements. The treatment of the benzyl quaternary ammonium salt with sodium amide or other alkali metal amide generates benzyl ammonium ylide. The following examples are illustrative [108, 116-119] ... 

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