Ammonium ylides examples

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... 

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. 

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... 

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. 

The chemistry of ammonium ylides formed from the reaction of cyclic amines with carbenes was found to be dependent on the ring size of the amine.52 For example, treatment of 1-benzylazetidine (104) with ethyl diazoacetate in the presence of a copper (II) catalyst afforded pyrrolidine 106 in 96% yield. This result is consistent with ammonium ylide formation followed by ring expansion. In contrast, treatment of 1 -phenethylaz-iridine (107) under identical conditions gave the fragmentation product 109 in quantitative yield. Similar results were observed for the reaction of aziridine 107 with dichlorocarbene.53 On the other hand, reaction of 1-phenethylpyrrolidine with ethyl diazoacetate in the presence of a... 

Sigmatropic rearrangements of cyclic sulfonium and ammonium ylides have been extensively used in ring contraction and ring enlargement methods. An example is shown in Scheme 55. 

Allenes can be easily prepared using the 3,2-sigmatropic rearrangement of ylidic intermediates. This methodology also provides a general route towards the synthesis of cumulenes. Some examples using sulfonium and ammonium ylides are collected in Table 5. ... 

The striking difference in behavior between nitrogen and sulfur ylides is illustrated once again with the examples collected in Scheme 103. In most of the cases involving the rearrangement of propargylic ammonium ylides, the allene (initial reaction product) can be isolated or identified as a component of the... 

Chiral auxiliary approaches have been examined for the production of enantioenriched products through [2,31-rearrangements. For example, Sweeney and coworkers treated N,N-dimethylammonium salts 186 with sodium hydride to generate ammonium ylides bearing Oppolzer s camphorsultam, which underwent diastereoselective [2,31-Stevens rearrangements to enantioenriched products 187 [Scheme 1S.44. Eq. Oppolzer s camphorsultam was also compatible with our group s palladium-catalyzed tandem allylic amination/[2,31-Stevens rearrangement of tertiary amines [Scheme 1S.44. Eq. 2) ... 

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. 

Concerted [2,3]-sigmatropic rearrangements of allyl and benzyl ammonium ylides, allyl sulfonium ylides, allyl sulfoxides, selenoxides, amine oxides and anions of allyl ethers have been reported. These are illustrated by die following general examples ... 

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] ... 

Sigmatropic rearrangements of benzyl quaternary ammonium salts are known as the Sommelet-Hauser rearrangements. The treatment of the benzyl quaternary ammonium salt with sodium amide or other alkali metal amide generates benzyl ammonium ylide. The following examples are illustrative [108, 116-119] ... 

Recently, Yadav and colleagues developed a catalytic aziridination reaction of imines via ammonium ylides and disclosed an example of asymmetric transformation using O-methyl quinine as a catalyst. Under similar reaction conditions (Na2C03, MeCN, 80°C, 18h) to Gaunt s, 20mol% catalyst promoted the reaction of N-tosyl benzaldimine with a-bromo acetophenone with high stereoselectivity (78% yield, 92% ee) in favor of the trans product (Scheme 20.31). However, only one example was presented. The generality of this reaction needs to be explored further [57]. 

The use of ammonium ylides in asymmetric [2,3]-rearrangements has been highlighted in several elegant settings [22, 23]. As an illustrative example, Baldwin demonstrated that the enolate derived from 213 could be rearranged into 214 as a single diastereomer (Equation 24) [113]. This transformation proved pivotal for the preparation of penicillin derivatives. 

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