Alkenes alkoxyamines

Another mechanism of nitroxyl radical regeneration was proposed and discussed in the literature [67-71]. The alkoxyamine AmOR is thermally unstable. At elevated temperatures it dissociates with cleavage of the R—O bond, which leads to the appearance of an [AmO + R ] radical pair in the cage of polymer. The disproportionation of this radical pair gives hydroxylamine and alkene. The peroxyl radical reacts rapidly with hydroxylamine thus... 

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. 

Reactions that convert the alkoxyamines to hy-droxylamines and alkenes can strongly limit the monomer conversion. These are either usual radical disproportionations between the nitroxide and the propagating radicals or concerted alkoxyamine decays. Both pathways lead to an exponential decrease of the concentration of the dormant chains with rate constant kdec = f)kd, where fn is the fraction of the side reaction concurring with radical coupling of alkoxyamine decay.57 kdec can be measured from the decay of the dormant alkoxyamine chains under nonscavenging conditions, and its relation with kd provides fn. From data of Fukuda et al. one can deduce fn = 0.4% for a TEMPO-polystyryl compound and fn = 1.1% for a di-tert-butylnitroxide-poly-terf-butylacrylate macroinitiator both at 120 °C.53,55 Similar small values of fn hold for TEMPO-cumyl (Scheme 10),22 TEMPO-1-phenylethyl,112 and a better mimetic compound for TEMPO-polystyryl.113 In these cases, fn probably represents the usual radical disproportionation. A much larger fn 25% holds for TEMPO—... 

Alkoxyamines are known to undergo thermal radical addition reaction to alkenes. High thermal efficiency of a microflow system over a batch system was shown in carboaminoxylation of alkenes using TEMPO-malonate [23]. In the batch system,... 

The products are the corresponding hydroxylamine 4 and the alkene 12 which is a co-unsaturated polymer in case of a polymeric alkoxyamine. In principle, 4 and 12 may also be formed by a concerted intramolecular nonradical Cope-type elimination of the alkoxymine ( ce) (path (b) or reaction (9), Scheme 4.5). 

Consequently, all the alkene 12 detected under such conditions was formed by the Cope-type elimination (b). On the other hand, alkene formed in the absence of thiophenol was generated by both paths. Recently, Marque et al showed that thermolysis of alkoxyamines in the presence of the scavenger PhSH induces chemically induced dynamic nuclear polarization (CIDNP). The CIDNP effect, detected by H-NMR, indicates that the intermolecular H-transfer occurs, in contrast to earlier reports,already in the spin correlated geminate (cage) radical pair, formed immediately after the cleavage of the NO C bond. 

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