Amination/ -Stevens rearrangement

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. ... 

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. 

Photolysis or thermolysis of heteroatom-substituted chromium carbene complexes can lead to the formation of ketene-like intermediates (cf. Sections 2.2.3 and 2.2.5). The reaction of these intermediates with tertiary amines can yield ammonium ylides, which can undergo Stevens rearrangement [294,365,366] (see also Entry 6, Table 2.14 and Experimental Procedure 2.2.1). This reaction sequence has been used to prepare pyrrolidones and other nitrogen-containing heterocycles. Examples of such reactions are given in Figure 2.31 and Table 2.21. 

Tertiary amines can react with electrophilic carbene complexes to yield ammonium ylides which usually undergo Stevens rearrangement (Figure 4.8) leading to products of a formal carbene C-N bond insertion. 

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. 

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

Other heterocyclic tertiary amines show a different behavior. Tertiary amines have been used as catalysts in dichlorocyclopropanation of olefins they probably give an ammonium ylide as the first step in the catalytic cycle.262 These ylides are usually unstable and undergo a variety of transformations such as the Stevens rearrangement and the Hoffmann elimination. 

A synthesis of a-( trifluoromcthyl)-a-amino esters 5 has been developed based on the [1,2] Stevens rearrangement of nitrogen ylides 4, obtained by the transition-metal-calalyzed decomposition of methyl 2-diazo-3,3,3-trifluoropropanoate (3) in the presence of tertiary amines.2... 

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. 

Reaction with a-silyltertiary aliphatic amines leads to results of the same type, including silyl- and non-sily 1-products, proceeding either from a Stevens rearrangement or a Hoffmann elimination.364... 

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. 

Finally, the ammonium ylide derived from 21 gave rise to amine 22 in 95% ee. This example also illustrates the radical pair nature of the Stevens rearrangement in that diamine 23 and alkane 24 were isolated as... 

We shall study the following problem A quarternary ammonium salt containing an electron withdrawing substituent W on one of the carbons attached to the nitrogen atom yields a rearranged tertiary amine on being treates with a base (Stevens rearrangement) (Eq. 56). 

The base-induced 2,3-shift in a benzyltrialkylammonium halide (Sommelet-Hauser synthesis) efrects an orr/io-selective aminomethylation of aromatics. A variation (orr/to-selective formylation) is shown in equation (37). Unfortunately, the 1,2-Stevens rearrangement (— 10% 143) of the intervening ylide competes with the 2,3-pathway (— 142). A reliable tool to circumvent this very general difficulty is still unknown. Nonetheless, 2,3-rearrangement pathways can be very efficient as demonstrated by the synthesis of the cyclic amine (144 equation 38). ... 

In the laboratory of F.G. West, the stereoselective silyl-directed [1,2]-Stevens rearrangement of ammonium ylides was investigated as a potential key step toward the enantioselective synthesis of various hydroxylated quinolizidines. The dimethylphenylsilyl group served as a surrogate for one of the hydroxyl groups in the product. The Fleming-Tamao oxidation was performed under Denmark s conditions to avoid oxidation of the tertiary amine to the corresponding A/-oxide, and the desired quinolizidine did was obtained in 81% yield. 

Ollis and coworkers reinvestigated the stereochemical outcome of the Stevens rearrangement and provided a detailed understanding of the mechanism of this reaction. Rearrangement of the optically pure ammonium salt (143) gave three products, (144), (159) and (160) in a ratio of 80 11 5 (Scheme 34). The amine (144) was optically active and degradation studies proved that migration occurred with more... 

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