Ammonium ylides, -Stevens rearrangement

Stevens Rearrangement. Ammonium ylides undergo a stereoselective Stevens [2,3]-rearrangement when treated with LDA to afford lV-methyl-2,3-disubstituted piperidines (eq 35)7 ... 

Scheme 2.53 [2,3]-Stevens rearrangement of a vinylaziridine-derived ammonium ylide 219.

The key step in the total synthesis of (—)-epilupinine 253 involved the ring expansion of a proline-derived spirocyclic ammonium ylide to give 252 through a [1,2] Stevens rearrangement, as shown in Scheme 51 <1997T16565>. 

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]. 

A ring enlargement process was used effectively to access the enantiopure pyrrolo [ 1,4]oxazepine-9a(7//)-carboxylate derivatives 142 and 143. The sequence involved copper (Il)-catalysed decomposition of an a-diazocarbonyl derivative attached to a chiral morpholinone, and a carbenoid, spiro-[5,6]-ammonium ylide, Stevens [1,2] rearrangement sequence. The Stevens and related rearrangements have considerable further potential for novel heterocyclic syntheses <00TA3449>. 

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. 

Fig. 4.8. Formation and Stevens rearrangement of ammonium ylides from acceptor-substituted carbene complexes.

Experimental Procedure 4.2.5. Ammonium Ylide Formation and Stevens Rearrangement Diethyl 2-Benzyl-2- [(ethoxycarbonyl)mefiryl](methyI)amino malo-nate [1241]... 

Naidu, B.N. The Stevens Rearrangement of Ammonium Ylides and Its Applications to the Synthesis of Azaheterocycles, a-Amino Add Derivatives and Optically Active (-)-Epilupi-nine Ph.D. Dissertation, University of Utah,... 

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. 

Recent advances in the Stevens rearrangement of ammonium ylides have been reviewed in terms of application to the synthesis of alkaloid natural products.147... 

Maeda, Y. Sato, Y. Mechanism of the Stevens rearrangement of ammonium ylides. /. Chem. Soc. Perkin Trans. 11997, 1491-1493. 

The first example of an ammonium ylide rearrangement was encountered in 1928 by Stevens and co-workers who observed that a novel [l,2]-benzyl shift occurred when ammonium salt 1 was heated in dilute... 

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... 

Recently, Padwa s group has encountered an interesting Stevens rearrangement sequence which occurred when a-diazo ketoamide 142 was subjected to Rh(II)-catalyzed conditions.66 In the presence of DMAD, the expected product 146 derived from the trapping of dipole 145 was isolated (57%) together with the unexpected lactam 144 (23%). In the absence of DMAD, lactam 144 was the only product obtained in 62% yield. The formation of 144 was attributed to the initial generation of ammonium ylide 143 followed by a [l,2]-benzyl shift. 

Ammonium ylides such as 3.62 in which none of the alkyl groups possesses a 3-hydrogen atom, but one has a 3-carbonyl group undergoes the Stevens rearrangement to give the amino ketone 3.63 (Scheme 3.26). 

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. 

Sato, Y., Yagi, Y., Koto, M. Ylide reactions of benzyldimethyl[(triorganosilyl)methyl]ammonium halides. J. Org. Chem. 1980,45, 613-617. Zhang, J. J., Schuster, G. B. Photo-Stevens rearrangement of 9-dimethylsulfonium fluorenylide. J. Org. Chem. 1988, 53, 716-719. 

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