Rearrangement of ammonium ylides

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]. 

Under similar profiles of raising in temperature, it was shown that the selectivity favoring 1,2 Stevens rearrangement is exemplified under the action of microwaves. A tentative explanation can be to consider that, under the action of radiation, the more polar mechanism (1,2 ionic shift) is favored when compared to less polar one (2,3 radical shift). Maybe this result is indicative of a competition between ionic and radical pathways. 

---

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

Table 4.16. Generation and rearrangement of ammonium ylides from diazocarbonyl compounds and tertiary amines.

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,... 

It has been noted that for the ammonium ylide generation copper catalysts such as copper(ii) acetylacetonate [Cu(acac)2] and Cu(hfacac)2 are superior over Rh(ii) catalysts. Sweeney and co-workers have recently reported copper-catalyzed [2,3]-sigmatropic rearrangement of ammonium ylide generated from tetrahydropyridines 150 and diazo ester 129 (Equation (22)). A detailed study on the reaction conditions has revealed that Cu(acac)2 is the best catalyst for this reaction. 

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. 

Heard, G. L. Yates, B. F. Competing rearrangements of ammonium ylides a quantum theoretical study. /. Org. Chem. 1996, 61, 7276-7284. 

A valuable part of the [2,3]-sigmatropic rearrangement of ammonium ylides is the fact that stereochemical information can be transferred. For example, Kaiser and co-workers stereoselectively alkylated the C-6 position of penicillin using the nitrogen ylide 46 derived from lactam 45.28 Quatemization of 45 with allyl bromide followed by ylide generation using sodium hydride effected the [2,3]-rearrangement. This resulted in the exclusive formation of P-lactam 47 in 75% yield. 

Other reactions. /3-Lactams, such as 182, were prepared in moderate to good yields by [2,3]-rearrangement of ammonium ylides produced by the reaction of copper carbenoids tethered to allylic amines (Scheme 77) <2001J(P1)3312>. The catalyst of choice in the generation of carbenoid/ylide from a-diazoketone precursor is copper(n) acetylacetonate. 

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. 

The [2,3]-sigmatropic rearrangement of ammonium ylides can lead to interesting heterocycles. Although it has been known for some time that the Simmons-Smith... 

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)... 

The rearrangement of ammonium ylides 27 derived from chiral amines affords chiral 3-butenals 28 in modest yield120. Critical to the observed diaslereoface selectivity of the rearrangement is the substrate-directed alkylation of amines 26 to afford asymmetric ammonium salts. The observed asymmetric induction is consistent with rearrangement through a transition state conformation in which the more substituted carbon (RL) of the auxiliary occupies an exo orientation. 

Concerning the Absence of Microwave Effects 209 4.8.4.6 Rearrangement of Ammonium Ylides... 

Applications of Stevens rearrangement of ammonium ylides to the synthesis of alkaloids 06T1043. 

Recent Advances In The Stevens Rearrangement Of Ammonium Ylides. Application To The Synthesis Of Alkaloid Natural Products Vanecko, J.A. Wan, H. West, F.G. Tetrahedron 2006, 62, 1043. 

The [2,31-Stevens rearrangement could be more generally utilized in S5mthesis if it were developed into an enantioselective process. Therefore, tremendous effort has been invested in recent years into the discovery of stereoselective [2,31-rearrangements of ammonium ylides for the generation of enantioenriched products. 

Rearrangement of Ammonium Ylides (Sommelet-Hauser Rearrangement) The... 

SCHEME 18.17 The Sommelet-Hauser rearrangement of ammonium ylides. 

Clark JS, Hodgson PB, Goldsmith MD et al (2(K)1) Rearrangement of ammonium ylides produced by intramolecular reaction of catalytically generated metal carbenoids. Part 2. Stereoselective synthesis of bicyclic amines. J Chem Soc Ptakin Trans 1 3325-3337 Miyashi T, Nishizawa Y, Fujii Y et al (1986) The intramolecular nitrene-type 1, 1 -cycloaddition reaction of allyl-substituted diazomethanes. J Am Chem Soc 108 1617-1618... 

The Sommelet-Hauser reaction, a [2, 3] sigmatropic rearrangement of ammonium ylides, is also an attractive method for ring expansion of nitrogen heterocycles. Recently... 

SCHEME 17.5. Synthesis of isopavine 18 by a [1,2]-Stevens rearrangement of ammonium ylide 17. 

---