Ammonium ylides, allylic rearrangements

Chem. Soc. Perkin Trans. 11999, 2439—2447. Blid, J. Somfai, P. Lewis add mediated [2,3]-sigmatropic rearrangement of allylic ammonium ylides. Tetrahedron Lett. 2003, 44, 3159-3162. 

Sigmatropic rearrangement of allylic ammonium ylides mediated by the combination of Lewis acid-nonionic phosphazene base was reported by Blid and Somfai [14], The... 

Scheme 7.11 [2,3J-Sigmatropic rearrangement of allylic ammonium ylides...

To address the need for a more general catal)Tic method of s)mthesizing allylic ammonium ylides for [2,3]-rearrangements that is amenable to enantioselective catalysis, our group recently developed a palladium-catalyzed tandem allylic amination/[2,3]-Stevens rearrangement of tertiary amines that proceeds through a palladium-n-allyl intermediate rScheme 15.34T Metal-catalyzed allylic aminations between primary or secondary amines... 

There are a number of [2,31-sigmatropic rearrangements related to the Mislow-Evans rearrangement but differing in the heteroatom moiety. While these are not the main focus of the current chapter, they present unique opportunities for synthetic applications, and several recent examples are oudined in the following. Another closely related process, the [2,3]-Meisenheimer rearrangement of allylic IV-oxides, is discussed separately in Chapter IS on ammonium ylide rearrangements. 

Allylic ammonium ylides generated in the presence of a strong base undergoes [2,3]-sigmatropic rearrangement. The following reactions are the illustrative examples [108-115] ... 

Rautenstrauch V. Sigmatropic reactions in carbanions. II) The rearrangement of allylic ammonium ylides. Helv. Chim. Acta 1972 55(6) 2233-2240. 

The rearrangements of allylic sulfoxides, selenoxides, and amine oxides are an example of the first type. Allylic sulfonium ylides and ammonium ylides also undergo [2,3]-sigmatropic rearrangements. Rearrangements of carbanions of allylic ethers are the major example of the anionic type. These reactions are considered in the following sections. 

Ammonium ylides can also be generated when one of the nitrogen substituents has an anion stabilizing group on the a-carbon. For example, quaternary salts of /V-allyl a-aminoesters readily rearrange to y,8-unsaturated a-aminoesters.286... 

Synthetically valuable [2,3]-sigmatropic rearrangements include those of allyl sulfonium and ammonium ylides and a -carbanions of allyl vinyl ethers. 

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]. 

Ylides lacking electron-withdrawing groups attached to the nitrogen atom also undergo this rearrangement. Rautenstrauch and co-workers demonstrated this point by transforming the symmetrical allylic ammonium salt 32 into amine 33. The overall yield for this process was 87%.23... 

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. 

Using simple allylic ammonium salts, Hill and co-workers showed that the rearrangement of rrans-(/ )-ammonium ylide 48 followed by... 

The reaction of dichlorocarbene with A, A -diethyl-3-methyl-2-butenamine (100) produced A V-diethyl-4-methyl-2-pentenamide (103) as the major product.51 The formation of this material was attributed to the generation of ammonium ylide 101 followed by a [l,2]-allylic shift to give intermediate 102 which then hydrolyzed during workup to produce amide 103. No product resulting from a [2,3]-sigmatropic rearrangement of ylide 101 was detected in the crude reaction mixture. 

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. 

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