Stevens migration

Keywords Iminosilanes / Adducts / Stevens Migration / Cycloadditions... 

If the pyridine adducts 8 and 9 are slowly heated in toluene to a temperature of 50°C they decompose under Stevens migration into 10 and 11 (Scheme 5) [5]. 

Scheme 5. Stevens migration of iminosilane-pyridine adducts.

In the case of elimination from (9), isoindole formation competes with 1,2-migration of the benzyl group (Stevens rearrtingement ), whichgives l-benzyl-2-m6thylisoindoline (10), and also with migration... 

For books, see Mayo, P. de Rearrangements in Ground and Excited States, 3 vols. Academic Press NY, 1980 Stevens, T.S. Watts, W.E. Selected Molecular Rearrangements Van Nostrand-Reinhold Princeton, 1973. For a review of many of these rearrangements, see Collins, C.J. Eastham, J.F. in Patai The Chemistry of the Carbonyl Group, vol. 1 Wiley NY, 1966, p. 761. See also the series Mechanisms of Molecular Migrations. 

When we allowed pentafluorophenyl-lithium to decompose in ether in the presence of an excess of N, ZV-dimethy laniline we obtained the compounds (92) 70, X = F), (94), the latter as the major compound, and a product which was shown to be (97). That this latter compound did not arise by metallation of 2V,lV-dimethylaniline followed by addition to tetrafluorobenzyne was shown by quenching the reaction mixture with deuterium oxide. No deuterium incorporation was detected. The compound (97) provides a rare example of a product derived by a Stevens rearrangement in which aryl migration has occurred b>. 

The last reaction shows that the benzyl group has a superior migration aptitude in the Stevens rearrangement. It is more reactive in nucleophilic... 

Hedgcore, H. R. and Stevens, W. S., 1991, Hydraulic Control of Vertical DNAPL Migration In Proceedings of the National Water Well Association of Ground Water Scientists and Engineers Conference on Petroleum Hydrocarbons and Organic Chemicals in Ground Water Prevention, Detection and Restoration, pp. 327-338. 

Cutaneous reactions such as rash or Stevens-Johnson syndrome are also consist with initiation through protein haptenation, although in this case dendritic cell activation/ migration and T-cell propagation are involved [31]. Other immune mediators such as cytokines, nitric oxide and reactive oxygen species which may be linked to the formation of reactive metabolites may also be implicated, as may specific processes occurring at the level of the keratinocyte. 

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. 

Scheme 2.6 1,2-Migration via a radical pair in a Stevens rearrangement of ylid 13.

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. 

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