Quaternary salts, Stevens rearrangement

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... 

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. 

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. 

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. 

A new approach to the morphine skeleton was demonstrated by the total synthesis of (+)-desoxycodeine-D by C.-Y. Cheng and co-workers." " The key step was the formation of the B ring by the Stevens rearrangement of a tetrahydroisoquinoline-derived quaternary ammonium salt upon treatment with phenyllithium. 

Aryl migrations also occur in Stevens rearrangement of quaternary ammonium salt salts (50, 84). 

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. 

The reaction of 102 with allyl bromide in refluxing acetone led to the quaternary salt 103. Treatment of 103 with f-BuOK gave a mixture of 104 as major (55%), 105 (5%) along with the Stevens rearranged product 106... 

The [2,3]-Stevens rearrangement is a thermal sigmatropic rearrangement of an ammonium ylide (38) to form unnatural amino acid derivatives 39 (Scheme 12). Traditionally, the ammonium ylides have been formed through alkylation of aminoesters 36 with aUcyl halides 37 to form quaternary salts followed by treatment with base. Although effective, the harsh conditions lead to side products and limited substrate scope. More recently, the coupling of diazoesters 40 and allylic amines 41 in the presence of metals like copper, rhodium, and palladium has been developed for the direct constmction of ammonium ylides 38 via metal carbenoid intermediates. " Although this approach represented an advance over the traditional alkylation chemistry, the use of diazoesters still limits the synthetic utility of these reactions. 

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

Giumanini, A. G., Trombini, C., Lercker, G., Lepley, A. R. Heterobenzyl quaternary ammonium salts. IV. 2-Thenyl group as terminus and migrating moiety in the Stevens and Sommelet rearrangements of a quaternary ammonium ion. J. Org. Chem. 1976,41, 2187-2193. 

Dunn, J. L., Stevens, T. S. Degradation of quaternary ammonium salts. VI. Effect of substitution on velocity of intramolecular rearrangement. J. Chem. Soc., Abstracts 1932, 1926-1931. 

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