Nitrone-mediated radical coupling

Scheme 4.11). The macroradicals are generated either through conventional polymerization initiated by TRI or from dormant chains pre-made by ATRP. The process is called ESCP (enhanced spin capturing polymerization) in the first case and NMRC (nitrone-mediated radical coupling) in the second. The formation of 21 is irreversible at the reaction temperature (<80°C), however,... 

The proposal by Dolphin of an oxaziridine mechanism for flavin mediated oxidations has been criticized by Rastetter s group (292) since oxygen insertion in enzymatic oxidations is not induced photochemically. What they have shown however is that nonenzymatic oxidations can be effected by a flavin N(5)-oxide (nitrone). Upon irradiation in the presence of a phenol, a flavin nitroxyl radical and a phenoxy radical are generated, as detected by EPR spectroscopy. The coupling of these two species leads to flavin and hydroquinone. 

New Acyclic Nitrone Spin Traps. - The range of new acyclic nitrone traps that have been synthesised is more limited than that of the related cyclic materials. Examples of some of these new materials are given in Scheme 3. This is due, at least in part, to the perception that these traps provide more limited data in terms of the range of hyperfine coupling constants than the cyclic nitrones, and hence decreased opportunities for definitive identification of radical adducts. Nonetheless these traps can have considerable advantages in that they often yield very persistent adducts, which can be of major benefit in determining whether a process is radical-mediated or not, before more intensive study to determine the exact nature of the species involved. This persistence is of major importance when the separation and subsequent identification (by other... 

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