Quaternary ammonium rearrangement

Chemical Properties. Reactions of quaternaries can be categorized iato three types (169) Hoffman eliminations, displacements, and rearrangements. Thermal decomposition of a quaternary ammonium hydroxide to an alkene, tertiary amine, and water is known as the Hoffman elimination (eq. la) (170). This reaction has not been used extensively to prepare olefins. Some cycHc olefins, however, are best prepared this way (171). Exhaustive methylation, followed by elimination, is known as the Hoffman degradation and is important ia the stmctural determination of unknown amines, especially for alkaloids (qv) (172). 

SOMMELET HAUSER Ammonkjmyfld rearrangement Rearrangement of quaternary ammonium ylids to aminas by aryl trarafer. 

A quaternary ammonium species 1, bearing an electron-withdrawing group Z a to the nitrogen center, can rearrange to a tertiary amine 3, when treated with a strong base. This reaction is known as the Stevens rearrangement. ... 

Hofmann rearrangement, 933 imide (-CONHCO—), 929 primary amine (RNH2), 916 quaternary ammonium salt, 917 reductive amination, 930 Sandmeyer reaction, 942 secondary amine (R2NH), 917 tertiary amine (R3N), 917... 

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 quaternary ammonium salts and tertiary benzylic... 

Partitioning of carbocations between addition of nucleophiles and deprotonation, 35, 67 Perchloro-organic chemistry structure, spectroscopy and reaction pathways, 25, 267 Permutational isomerization of pentavalent phosphorus compounds, 9, 25 Phase-transfer catalysis by quaternary ammonium salts, 15, 267 Phosphate esters, mechanism and catalysis of nucleophilic substitution in, 25, 99 Phosphorus compounds, pentavalent, turnstile rearrangement and pseudoration in permutational isomerization, 9, 25... 

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... 

Demercuration of organomercury compounds is a critical step in synthetic procedures, which involve mercuration-initiated cyclization reactions [e.g. 41], Many of the standard procedures for demercuration result in rearrangement or ring cleavage of the system, but reductive carbon-mercury cleavage (e.g. Scheme 11.4) with an excess of the quaternary ammonium borohydride is effective under phase-transfer conditions [e.g. 42,43]. 

Wittig rearrangement of benzylic quaternary ammonium salts upon treatment with alkali metal amides via the ammonium ylide intermediates. 

Miscellaneous PTC Reactions The field of PTC is constantly expanding toward the discovery of new enantioselective transformations. Indeed, more recent applications have demonstrated the capacity of chiral quaternary ammonium salts to catalyze a number of transformations, including the Neber rearrangement (Scheme 11.19a), ° the trifluoromethylation of carbonyl compounds (Scheme 11.19b), ° the Mannich reaction (Scheme 11.19c), and the nucleophilic aromatic substitution (SnAt)... 

Cleavage of a-aminoketones and their quaternary ammonium salts by sodium amalgam or zinc dust and acid has been used in synthetic procedures. This process was a key step in determining the stereochemistry of the Stevens rearrangement for... 

Quaternary ammonium N-F reagents, 69, 2 salts, rearrangements of, 18, 4 Quinolines, synthesis of,... 

Asymmetric induction in the Neber rearrangement was also obtained under phase-transfer conditions with chiral quaternary ammonium bromides 544 as catalysts (equation 243). Moderate enantioselectivities (30-70% ee, 60-95% yield) were observed, but there is still an opportunity for extending the full synthetic utility of this classical rearrangement. 

Essentially the same mechanism is likely to be involved in an electrochemical version of the Stevens rearrangement. The mechanism of this reaction is not known with certainty however, it is known to be intramolecular and to involve deprotonation of quaternary ammonium salts to give nitrogen ylids which rapidly rearrange. The scheme set out in Scheme 9 is therefore entirety plausible. 

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

Rearrangement of N-haloamines 8-22 Rearrangement of quaternary ammonium salts and tertiary benzylic amines (Stevens)... 

Sigmatropic rearrangements of quaternary ammonium salts 8-38 Rearrangement of benzidines... 

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