Stevens-Sommelet rearrangement

The rearrangement of ammonium ylides (Stevens-Sommelet rearrangement) or sulfonium ylides the X-Y fragment is an anion a to a positively charged nitrogen (R3 N- CR2) or sulfur (R2,+S- CR2)... 

Ammonium ion, JV-(2-thenyl)-N-benzyldimethyl-Stevens and Sommelet rearrangement, 4, 800 Ammonium salts, diallyldialkyl-polymerization, 1, 293 Ammonium salts, 2-pyrrolylmethyl-nucleophilic substitution abnormal, 4, 244 Sommelet rearrangement, 4, 244 Ammonium salts, trimethyl(l,3,5-triazinyl)-applications, 3, 525 Amobarbital, 3, 150 Amodiaquine, 1, 145 Amolanone applications, 4, 708... 

Sommelet rearrangement, intermediate temperatures favor Stevens rearrangement,- and high temperatures promote elimination to form isoindoles. Treatment of 2-methyl-2-o-tolylmethylisoindolinium... 

Reaction of benzyne with tertiary aliphatic amines to give anilines via Sommelet-Hauser and/or Stevens-type rearrangements of the intermediate ylid has been documented.362 363... 

A mixture of 1-methyl-2-p-methoxybenzyl-3,4-diethyl-3-piperi-deine (156), 1 - methyl- 3,4-diethyl - 4 -p- metho xybenzyl- 2-piperideine (157), and 1-methyl- 2-(2-methyI-5-methoxyphenyl)-3,4-diethyl-3-piperideine (158) was obtained from 1-methyl- 1-p-methoxybenzyl-3,4-diethyl-3-piperideinium chloride (155). Compounds 156 and 157 were formed by the Stevens rearrangement, whereas the formation of compound 158 was due to the Sommelet rearrangement.1296... 

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. 

Lepey, A. R., Giumanini, A. G. Stevens and Sommelet rearrangements. Mechanisms of Molecular Migrations 1971, 3, 297-440. 

V-Benzyl-/V,/V-dirnethy Ian Mini urn bromide 30 reacts with sodium amide in liquid ammonia to give both the product of 1,2-shift 33 (Stevens rearrangement) and the ortho-substituted compound 34 (Sommelet rearrangement) via the intermediate ylides 31 and 3254 (equation 13). 

The ylides 31 and 39, the key intermediates of both the Stevens and Sommelet rearrangement discussed above, can be generated also by addition of benzyne 38 to N-alkylamines. Thus, generation of benzyne 38 in the presence of A /V-dimethylbenzylamine... 

The Stevens and the Sommelet rearrangement have their analogs in rearrangement of sulfonium salts by strong bases. 

Figure 13 Competition between the Sommelet-Hauser (top) and Stevens (bottom) rearrangements in the ring expansion of nitrogen heterocycles...

For a method that uses nonbasic conditions, and gives high yields of the Sommelet-Hauser product, with little or no Stevens rearrangement, see Nakano, M. Sato, Y. J. Org. Chem., 1987, 52, 1844 Shirai, N. Sato, Y. J. Org. Chem., 1988, 53, 194. 

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]. 

There can be competition between Sommelet-Hauser and Stevens Rearrangement mechanisms ... 

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. 

The presence of an alkyl group or not on the benzylic carbon atom has little influence on the result (example 2). The Sommelet-Hauser rearrangement product is not obtained as its exo-1 -alkylidene-cyclohexadi-2,4-ene precursor is stable (allowed typical cyclohexadiene chemistry) and isolable as a 1 5 mixture (35% yield) of the two stereoisomers. Styrene is also obtained as the major product (50%) whereas the Stevens product is formed in trace amounts. Triene A is converted quantitatively into 2-ethylbenzylamine under treatment with diluted KOH at 60 °C for 0.5 h in ethanol.368... 

Modification of the stereochemistry of the reaction has been demonstrated by studying desilylation reaction of cis- and mmy-2-methyl-1 -(phenyl)isoindolinium 2-methylides. It has been established that cw-isomer leads preferentially to the Sommelet-Hauser rearrangement product (eight-membered ring formed) whereas the trans-isomer leads predominantly to the Stevens rearrangement product.374... 

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