Nitronates carbon-centered radicals

Cyclization of nitro-stabilized radicals provides another method for the generation of cyclic nitronates (221). Oxidation of the aci-foim of nitroalkanes with ceric ammonium nitrate generates the ot-carbon centered radical, which in the presence of an alkene, leads to the homologation of the a-radical. In the case of a tethered alkene of appropriate length, radical addition leads to a cyclic nitronate (Scheme 2.20). 

Nitrones arc generally more stable than nitroso-compounds and arc therefore easier to handle. However, the nitroxides formed by reaction with nitrones [e.g. phenyl /-butyl nitrone (109)]483 484 have the radical center one carbon removed from the trapped radical (Scheme 3.86). The LPR spectra are therefore less sensitive to the nature of that radical and there is greater difficulty in resolving and assigning signals. Nitrones are generally less efficient traps than nitroso-compounds.476... 

Addition ofN-, S- and P-Nucleophiles The reaction of nitrones with heteroatom centered nucleophiles has been little investigated and are mainly applied to the synthesis of new heterocyclic systems and stable nitroxyl radicals, containing a heteroatom at the a-carbon atom. 

We explored the question of charge transfer in the transition state by a simple HMD approach. If one imagines tearing away carbon-2 from vinyl nitroxide the reverse process would resemble at the Initial stages the addition of a kind of methyl radical (i.e. a radical with an unpaired electron in a p-orbital centered on carbon) to the nitrone function ... 

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