Amine oxides allyl, -sigmatropic rearrangements

Sigmatropic Rearrangements of Allyl Amine Oxides The Meisenheimer Rearrangement... 

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. 

A7-Ally] amine oxides represent the general pattern for [2,3]-sigmatropic rearrangement where X = N and Y = O The rearrangement provides O-allyl hydrox-ylamine derivatives. 

Sigmatropic rearrangement of allylic tertiary amine-A -oxides to give O-allyl hydroxylamines ... 

Among the first reported synthetic methods for alkene isosteres, a sigmatropic rearrangement of oxidatively activated allylic selenides to provide Boc-protected allylic amines was used for the synthesis of the D,L-Tyn i[is, CH=CH]Gly isostereJ711 The method resulted in a racemic dipeptide isostere, and only a Gly residue at the C-terminus is possible. It is no longer competitive compared with more recent methods using rearrangement of allylic tri-chloroacetimidates. 

Enantioselective catalysis has also been used for the synthesis of optically active sulfimines [51]. By application of 5 mol % of the bisoxazoline-copper(I) catalyst 80, the sulfide 77 is oxidized catalytically to 78 which undergoes a [2,3]-sigmatropic rearrangement to give allyl amine 79 in 80% yield and with 58% ee (Eq. (20)). Other alkenes were found to give lower ee. 

Amine oxides, sulfoxides, and selenoxides all undergo the [2,3] sigmatropic rearrangement. The equilibrium between allyl sulfoxides and allyl sulfenates lies on the side of the sulfoxide, but the equilibrium can be pushed toward the sulfe-nate by reduction of its O-S bond. 

Sulfides can be oxidized to sulfoxides by reaction with NCS in methanol (0°C, 1 h). Similarly, selenides couple with amines when activated by NCS to form selenimide species. These have been generated from allylic selenides in order to prepare allylic amines and chiral secondary allylic carbamates by [2,3]-sigmatropic rearrangement (eq 8). ... 

In 1919, Meisenheimer reported a detailed account of an unusual transformation of methyl-allyl-aniline 3 in the presence of benzoic peracid 4, which yielded the N,N,0-trisubstituted hydroxylamine product 6 through amine iV-oxide 5 tScheme IS.21. Although the mechanism of the process was not fully appreciated at the time, this discovery was one of the earliest examples of a [2,3]-sigmatropic rearrangement, and it served as the foundation for the discovery and development of many [2,3]-rearrangements of reactive zwitterionic substrates. 

Similarly, Reetz and Lauterbach studied the diastereoselective [2,3]-rearrangement of chiral amine iV-oxides 71, which were generated from enantioenriched chiral allylic amines 70 tScheme These sigmatropic rearrangements generated O-allylhydroxylamine... 

Formation of O, N, A -trisubstituted hydroxylamines from tertiary amine oxides via [1,2]-R group migration, or [2,3]-sigmatropic rearrangement when R = allyl ... 

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 ... 

Sigmatropic rearrangement of allyl amine oxides is known as the Meisenheimer rearrangement. This rearrangement provides O-aUyl hydroxylamine derivatives. Some examples are [137, 138] as follows ... 

---