Rearrangement of amine oxides

There are not many examples of the direct transformation of an allylic amino to a rearranged oxygen functionality. One example is found in the Meisenheimer rearrangement of amine oxides, which occurs with almost complete chirality transfer, as seen in equation (23). ... 

C. Rearrangements of /-Amine Oxides Rearrangements with Migration to an DEFICIENT Nitrogen A. Beckmann Rearrangement... 

Other examples of [2,3] sigmatropic rearrangements involve amine oxides and diazenes ... 

The thermal rearrangement of 1,5-dienes 1 to yield the isomeric 1,5-dienes 2, is called the Cope rearrangemenC —not to be confused with the thermolysis of amine oxides, which is also named after Arthur C. Cope. 

Table 14 Oxidation and rearrangement of amines 191 using frar)s-2-phenyi-suifonyi-3-phenyioxaziridine 33 <1999J(P1)2327>...

Cleavage of amine oxides to produce an alkene and a hydroxylamine is called the Cope reaction or Cope elimination (not to be confused with the Cope rearrangement, 18-32). It is an alternative to 17-7 and 17-8. The reaction is usually... 

Scheme 14.21 Enantio- and diastereoselective synthesis of homoallylic fragments. CHAPTER 15 [2,3]-REARRANGEMENTS OF AMMONIUM ZWITTERIONS Scheme 15.1 Sigmatrnpic 12.31-rearrangements of reactive ammonium zwitterioas. Scheme 15.2 Meisenheimer s original report of an amine N-oxide rearrangement. Scheme 15.3 12.31- and ri.21-Meisenheimer rearrangements of amine jV-oxides.

Scheme 1 S.27 Proof of catalysis for the r2.31-rearrangement of amine iV-oxides.

Scheme 1S.28 Palladium-catalyzed enantioselective r2.31-rearrangement of amine N-oxides.

The [2,3]-rearrangement of amine iV-oxides was utilized in an efficient S5mthesis of 2,6-dimethyl-l,5-heptadien-3-ol acetate 61, a pheromone of the insect Pseudococcus comstocki tScheme lS.12id Dimethylpyridine 55 was converted in two steps into silylated piperidine 56, which was oxidized with m-CPBA to generate cyclic amine A-oxide 57. Sila-Cope elimination furnished O-silylhydroxylamine 58, which was methylated and desilylated in the presence of Mel and CsF to yield acyclic amine A-oxide 59. Heating this ammonium zwitterion facilitated the [2,3]-Meisenheimer rearrangement to O-allylhydroxylamine 60, which was transformed to the desired pheromone 61 in three steps. 

Based on the ability of Pd(OAc)2 to accelerate the [2,3]-rearrangement of amine iV-oxide 114, we explored chiral palladium(ll) salts to catalyze the enantioselective rearrangement. When we treated amine iV-oxides 116 with Pd(OAc)2 and chiral phosphoramidite 118, chiral O-allylhydroxylamines 117 were isolated in 80-85% ee (Scheme 1S.28V Subsequent optimization revealed the beneficial effect of methanol and meta-chlorobenzoic acid (m-CBA) as additives, allowing the isolation of chiral nonracemic O-allylhydroxylamines 117 with greater than 90% enantioenrichment. This palladium-catalyzed enantioselective [2,31-rearrangement can tolerate a wide variety of functional groups in the amine N-oxide substrate. For example, we can synthesize chiral allylic hydrojq lamine products with reactive functional groups such as alcohols and aldehydes, which are inconpatible with many other methods for the synthesis of chiral alcohol derivatives. 

Scheme lfi.29 Catalytic cycle of palladium-catalyzed [2,3]-rearrangement of amine JV-oxides. 

Part I. The Reactions of Amines Oxidation, Reduction, Addition, Substitution, and Rearrangement Part II. Some Organophosphorus Chemistry... 

The oxidation of aromatic acetals by A-chloronicotinamide in MeCN is zero-order in acetal. The rate is marginally affected by the ionic strength and nicotinamide but decreases significantly with increase in dielectric constant of the medium. CF3CH2OH is a useful solvent for the oxidative rearrangement of aminals by A-chlorosuccinimide which proceeds via the intermediacy of in situ formed chloroami-nals that produce 3,4-dihydroquinazolines. ° ... 

---