Stevens rearrangement intramolecular

The aza-[2,3]-Wittig rearrangement of a vinylaziridine-derived quaternary azir-idinium ylide (i.e., [2,3]-Stevens rearrangement) has recently been reported (Scheme 2.53) [86], The aziridinium ylide 219, generated by the intramolecular reaction of a copper carbenoid tethered to a vinylaziridine, underwent a [2,3]-Ste-vens rearrangement to furnish the bicydic amine 220 with the indolizidine skeleton. 

Intramolecular N-alkylation of tertiary amines, followed by Stevens rearrangement, enables rapid preparation of elaborate polycyclic structures [1235-1238]. Illustrative examples are given in Table 4.16. 

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. 

Van den Berg et al. suggested an intramolecular Stevens rearrangement of the oxo-nium ylide to ethyl methyl ether to interpret carbon-carbon bond formation463 [Eq. (3.55)]. Olah and coworkers, however, provided evidence (based on isotopic labeling studies) that the oxonium ylide undergoes intermolecular methylation to ethyl dimethyloxonium ion [Eq. (3.56)] instead of Stevens rearrangement 447... 

If the Stevens rearrangement is a concerted reaction, it is a symmetry-forbidden process based on the Woodward-Hoffmann rules. Indeed, it was shown to occur via an intramolecular hemolytic cleavage-radical pair recombination process, which explains the lack of crossover products and the observed retention of configuration at the migrating... 

More complex and synthetically useful applications of the Stevens rearrangement have been reported. Kondo, for example, has shown that the ylide (89), formed from (88) by an intramolecular carbene re-... 

Ethylene is heavily d - and d3-substituted indicating that it is formed mainly from CDgNg itself, and not through intramolecular 8-elimination from the ylide. This is taken as evidence against a Stevens rearrangement as the predominant pathway. 

A mechanism that has received a great deal of attention is the oxonium ylide mechanism.Dimethylether is methylated to trimethyloxonium, which is subsequently deprotonated to form surface associated methylene-dimethyloxoniumylide. The next step is either an intramolecular Stevens rearrangement, leading to the formation of methylethyl-ether, or an intermolecular methylation, leading to the formation of ethyl-dimethyloxoniumion. In both cases ethylene is obtained via jS-elimination. 

The reaction of 5-acetoxy-5,6,7,8-tetrahydroisoquinoline 109 with Mel followed by reduction afforded the octahydroisoquinoline 110, which upon treatment with ethyl chloroformate followed by hydrolysis gave 111. The condensation of 111 with 2-bromoisovanillin afforded 112, which was reduced to give the benzyl alcohol intermediate 113. Heck reaction of 113 led to the formation of 0-ring affording 115. The yield of the above intramolecular cyclization was increased significantly via prior protection of the alcohol in 113 as silyl ether 114. Conversion of 115 to benzyl chloride 116 was achieved via the treatment with NCS and triphenylphosphine. Further, Heck reaction of 116 afforded the tertiary amine 117 via an intramolecular A -benzylation. The amine 117 was converted into the corresponding iV-methylammonium iodide 118, which was then subjected to Stevens rearrangement with PhLi to afford ( )-desoxycodeine 119 in 83 % yield. ... 

Hanessian S, Mauduit M. Highly diastereoselective intramolecular [1,2]-Stevens rearrangements-asymmetric syntheses of functionalized isopavines as morphinomimetics. Angew. Chem. Int. Ed. 2001 40(20) 3810-3813. 

The synthesis of 3-benzylcyclobutanone (3) is an illustration of an overall intramolecular alkylation of an acyl anion equivalent (Section 5.9). The a,a>-dihalide is 2-benzyl-l,3-dibromopropane, and the acyl anion equivalent is methyl methylthiomethyl sulphoxide2 the product is 1-methylsulphinyl-l-methylthio-3-benzylcyclobutane which is obtained as a mixture of cis/trans isomers [(9) and (10)] (Expt 7.3). Aqueous acid hydrolysis in ethereal solution unmasks the carbonyl group. The possible mechanism of the reaction is via a Stevens-type rearrangement of the intermediate sulphur ylide, which may proceed in a pericylic, radical or ion pair fashion. 

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. 

A carbanionic mechanism similar to that proposed by Wittig and Krauss (33) involving a Steven s rearrangement can reasonably follow (Equation 5), i.e., an intramolecular attack on ylide (III) methyl forming dimethylethylamine. Protonation of dimethylethylamine followed by Hoffmann elimination (Equation 5a) would yield ethylene. 

The intermolecular nature of the C1-C2 transformation step was shown by experiments using mono- C labelled dimethyl ether and analyzing the isotopic composition of the product ethylene. The intramolecular Stevens-type rearrangement under the reaction conditions was clearly ruled out. 

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