SOMMELET-HAUSER Ammonium Ylide

Ammonium ylides can isomerize to (1,2) rearrangement products (Stevens rearrangement) or to (2,3) shift products (Sommelet-Hauser sigmatropic rearrangement) when allyl or benzyl are located on the nitrogen atom. A strong microwave effect is noticed (Eq. 66) [116]. 

Another type of ylidic rearrangement, the Sommelet-Hauser rearrangement, was discovered later, in 1937, by Sommelet and studied extensively by Sommelet and by Hauser. This transposition involves the base-promoted rearrangement of non stabilized ammonium and sulfonium ylides. Thus, the ammonium salt (11), when heated with alkali, gave cleanly the substituted diphenylmethane derivative (12 Scheme 5). Wittig found that the dibenzyl ammonium salt (13) reacted with phenyllithium giving two... 

In 1930, Ingold and Jessop reported the rearrangement of the fluorenyl ylide (412).Compound (414) was obtained in what can be considered as the first example of a Sommelet-Hauser reaction (Scheme 106). In 1937, Sommelet described the base-catalyzed transformation of the benzhydryl ammonium bromide (415) into the substituted benzylic amine (416 Scheme 107, equation a)." Wittig found later that reacting the salt (417) with phenyllithium produced two amines, (418) and (419). The former is derived from a Sommelet-Hauser 3,2-rearrangement, whereas the latter comes from a Stevens... 

Several limitations of this base-promoted rearrangement are worthy of mentioning (a) when structurally feasible, both Stevens and Sommelet-Hauser reactions will compete (b) certain substituents on the aromatic ring, e.g. Cl, CN, NO2, prevent the formation of the ylide and no rearrangement takes place (c) if a p-hydrogen is present on the ammonium salt, elimination becomes yet another undesirable side reaction, In an attempt to overcome these limitations, Sato has utilized the fluoride-induced desilylation of... 

Rearrangement of Ammonium Ylides (Sommelet-Hauser Rearrangement) The... 

SCHEME 18.17 The Sommelet-Hauser rearrangement of ammonium ylides. 

Sigmatropic Rearrangements of Benzyl Ammonium Ylides 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] ... 

The Sommelet-Hauser reaction, a [2, 3] sigmatropic rearrangement of ammonium ylides, is also an attractive method for ring expansion of nitrogen heterocycles. Recently... 

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