Ammonium salts, alkyl rearrangement

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. ... 

Rearrangement of arylamines or aryl alkyl ammonium salts... 

STEVENS REARRANGEMENT. Migration of an alkyl group from a quaternary ammonium salt to an adjacent carbanionic center on treatment with strong base. The product is a rearranged tertiary amine, sulfonium, or sulfide. 

The thio-Claisen rearrangement can also be performed with secondary thioamides, providing allylation on the nitrogen atom rather than carbon atom. An elaborate example was reported by Fuchs and Smith [183]. They introduced an allyl ammonium salt to achieve SN2 alkylation of sulfur, and the product readily rearranged to furnish the expected thiolactam. However they finally preferred to employ in the first step an allyl mesylate, which was more easily synthesised. 

Alkylation of 1-vinyl tetrahydroisoquinoline with ethyl bromoacetate afforded the ammonium salt in high yield (Equation 43). Treatment of this compound with DBU in THF at room temperature gave the [2,3]-sigmatropic rearrangement product 305 in 70% yield. The product consisted of a mixture of isomers in an (E)/(Z)-ratio of 96 4 <2005JOC5519>. 

N-Alkylation—Secondary Mannich bases can give the corresponding tertiary derivatives by treatment with particular alkylation agents, such as epoxides (affording P-ami-noalcohols) and acrylic derivatives. Tertiary Mannich bases, mostly, are submitted to N-alkylation in order to produce stable quaternary ammonium salts to be subsequently subjected to deamination (Sec. A.2). However, different quaternary ammonium byproducts can be readily given by the reaction. " For instance, a base-catalyzed rearrangement is afforded by allyl ammonium salts 365 (Fig. 144), obtained by N-alkylation of acetylenic Mannich bases with ally] halides. " In the presence of sodium hydride, the compounds 365 yield a wide range of 3-amino-5-hexen-l-yne derivatives 366. 

Thermal decomposition of quaternary ammonium salts and bases is most valuable in structural investigations of amines, particularly heterocyclic secondary amines (Hofmann exhaustive methylation). The course of the elimination (A or B) is determined by the nature of the four alkyl groups on the nitrogen atom. The reaction has found little use in the synthesis of pure olefins. The yields are low even when three of the alkyl groups are methyl radicals. Carbon-skeleton rearrangement does not occur. Thus, the only olefin obtained by pyrolysis of pinacolyltri-methylammonium hydroxide, (CHj),CCH(CHj)N(CHj)j OH, is /-butylethylene (50%). ... 

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... 

It should be noted that heating the free imidate causes the so-called Chapman rearrangement (Equation (7)),149 while heating the imidate salts causes decomposition to the corresponding alkyl halide and amide (Equation (8)), and in water, imidates (imidate salts) hydrolyze to corresponding esters and ammonium salts (Equation (9)). 

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). 

The rearrangement of ammonium ylides 27 derived from chiral amines affords chiral 3-butenals 28 in modest yield120. Critical to the observed diaslereoface selectivity of the rearrangement is the substrate-directed alkylation of amines 26 to afford asymmetric ammonium salts. The observed asymmetric induction is consistent with rearrangement through a transition state conformation in which the more substituted carbon (RL) of the auxiliary occupies an exo orientation. 

Sulfonium and ammonium salts are prepared readily by alkylation of sulfides or amines. For example, allylation of the amine 318 gave the intermediate ammonium salt 319 (3.205). Deprotonation to the ylide with sodium hydride was followed by [2,3]-sigmatropic rearrangement at room temperature to give the peni-cilhn derivative 320. In a synthesis of y-cyclocitral, the sulfonium salt 321 was prepared by alkylation of 1,3-dithiane and was converted to the ylide 322 and hence the rearranged product 323 (3.206). 

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. 

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