Alkoxy amine

The synthesis of alkoxy amines 2 by addition of organometallic reagents to the C-N double bond of oxime ethers 1 is plagued by the propensity for proton abstraction a. to the C-N double bond, the lability of the N-O bond and the poor electrophilicity of the oxime ethers. Therefore, frequently no products, undesired products or complex mixtures are obtained. The result depends on the substrate, organometallic reagent, solvent, temperature and additives1 6. 

Conversion of AT-alkoxy amines with ImCSIm at room temperature in ether produced, instead of N-alkoxythiocarbamoylimidazoles, the corresponding zwitterionic compounds 21 161... 

The same group recently disclosed a related free radical process, namely an efficient one-pot sequence comprising a homolytic aromatic substitution followed by an ionic Homer-Wadsworth-Emmons olefination, for the production of a small library of a,/3-unsaturated oxindoles (Scheme 6.164) [311]. Suitable TEMPO-derived alkoxy-amine precursors were exposed to microwave irradiation in N,N-dimethylformam-ide for 2 min to generate an oxindole intermediate via a radical reaction pathway (intramolecular homolytic aromatic substitution). After the addition of potassium tert-butoxide base (1.2 equivalents) and a suitable aromatic aldehyde (10-20 equivalents), the mixture was further exposed to microwave irradiation at 180 °C for 6 min to provide the a,jS-unsaturated oxindoles in moderate to high overall yields. A number of related oxindoles were also prepared via the same one-pot radical/ionic pathway (Scheme 6.164). 

FIGURE 1.2. Formation of nanoparticles of metal oxide by reverse micelle method. A solution of inverse micelles is first formed by adding a long-chain alkylamine to a toluene solution. A small amount of water is trapped in the reverse micelle core. Mixing the reverse micelle solution with an aluminum alkoxy amine adduct results in hydrolysis of the aluminum alkoxide adduct and formation of nano-sized particles of aluminum oxyhydroxide after drying. These particles are shown in the SEM picture above. 

The incorporation of TEMPO alkoxy amine at the end of a PE chain has been achieved [99]. The dialkylmagnesium compound in ethylene polymerization was adopted as a chain transfer agent, as mentioned above. It was also reported that PE-TEMPO and terminally N-(2-mcthyl-2-propyl)-N-(l-diethylphosphono-2,2-dimethylpropyl)-N-oxyl PE were synthesized by the reaction with di-polyethylene magnesium produced in ethylene polymerization. They were used for CRP of n-butyl acrylate, leading to PE-h-PnBA. 

Preparation of Aziridines by Oxidation of Amines, Acylhydrazines, and Alkoxy Amines in the Presence of Alkenes... 

The oxidation of amines, acylhydrazines, and alkoxy amines described in this section involves the formation of nitrenes or other intermediates, depending on the nature of the nitrogen substituent and the oxidant, although lead tetraacetate is commonly employed. For example, a nitrenium ion or an amino lead derivative was proposed as the intermediate in the oxidation of alkoxyamines with lead tetraacetate 2. However, evidence has been provided that the jV-acetoxy species is the intermediate in the aziridination of alkenes with V-aminophthal-imide and /V-aminoquinazolinone, where a mechanism analogous to the Bartlett mechanism for the peracid epoxidation of alkenes should be operating3,4. 

In addition to providing hydroxy (alkoxy) amines, the reaction of oximes" or oxime ethers " with or-ganometallic reagents can generate additional products. The propensity for proton abstraction a to the carbon-nitrogen double bond, the existence of mixtures of ( )- and (Z)-oxime isomers, the lability of the nitrogen-oxygen bond coupled with the poor oxime reactivity all contribute to the variability of this reaction. 

Nitroveratryl Carbamate (Nvoc—NR2). The use of the Nvoc group for protection of an alkoxy amine was demonstrated in a synthesis of a modihed tRNA. ... 

The key feature of the use of a dormant species may be seen in the following general scheme (Scheme 1.32) that involves complexation of the propagating species by means of a stable nitroxide radical (Hawker et al, 2001). The P -0 bond of the alkoxy amine P -0-NR is thermally labile at the polymerization temperature, so this becomes the site for the insertion of monomer. Propagation then occurs at a rate that is much slower than for a simple free-radical addition reaction since the propagating radical concentration (which is governed by the position of the equilibrium with the alkoxy amine... 

Scheme 1.32. Nitroxide-mediated polymerization showing formation of the dormant polymeric alkoxy amine species.

The initiation of the polymerization shown above may take place from a preformed alkoxy amine with an end group commensurate with the monomer, M. This is shown in Scheme 1.33 for styrene polymerization (Hawker et al, 2001). 

While the initial alkoxy amines were based on the nitroxyl mdical TEMPO (2,2,5,6-teframethyl piperidinyloxy) as shown above, this system is of limited applicability because of the high tempemtures (>125 °C) and long polymerization times (>24 hours)... 

In the sequence of reactions shown in Figure 1, the chain scission reactions of the alkoxy radical PO are important in the formation of a crack and thus embrittlement. The reactions in the presence of the nitroxide and hindered phenol stabilizers are modified by competition with the stabilization reactions that lead to either an inert, non-radical alkoxy amine product (R2NOP) or, for a hindered phenol, a stable radical (A-) that cannot initiate further oxidation. 

When the nitroxide is present, the alkyl peroxy radicals POO and the resultant hydroperoxide POOH are still formed, but the concentration is reduced due to the competition between oxygen and nitroxide for the alkyl radicals P. The rates of these reactions are given in Figure 2 for homogeneous kinetics. The extent of this competitive reaction may be estimated by the decrease in the slope of the CL - time curves in the retardation period as shown in Figure 3 and also by the formation of the alkoxy amine R2NOP. The concentration of the alkoxy amine R2NOP may be measured by fluorescence (see next section). 

The pro-fluorescent nitroxide TMDBIO when it reacts with an alkyl radical generates a fluorescent alkoxy amine so the fluorescence then becomes an integral measure of the number of such reactions that have taken place (2). This is seen in Figure 5 below for a sample of PP before and after oxidation at 150°C. 

Propargyl amines. a-Alkoxy amines undergo ionization in the presence of Sn(OTf)2, enabjing reaction with alkynylstannanes to give propargyl amines. 

During 1981-1983, Kozlowska-Gramsz and Descotes published several pa-pers dealing with the preparation of aminosaccharide derivatives from cyclic vinyl ethers and glycals. The key step was aziridination of the double bond by photochemically generated ethoxycarbonylnitrene, which produced 1,2-epi-mines as intermediates. The 1,2-epimines were cleaved in situ by the alcohol present in the reaction mixture to give vicinal alkoxy amines as mixture of stereoisomers. 

Primary alkoxy amines, RONHa. Direct alkylation of hydroxylamine results in attack on nitrogen to give RNHOH. Substances of the type RONHa can be prepared in two steps as shown. ... 

NO reacts v dth ("scavenges ) a polymer radical or other free radical (R ), deactivating it and forming an alkoxy amine (NOR). 

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