Fluoro spin adducts and their modes of formation

The reactions of two fluorinating reagents, XeF2 and N-fluorodibenzenesulfonamide [(PhSO2)(2)N-F], with several spin traps have been investigated, In dichloromethane, the strong oxidant XeF2 cleanly gives fluoro spin adducts with N-tert-butyl-alpha-phenylnitrone (PEN) or 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) according to a mechanism mediated by the radical cation of the spin trap, In both cases, further fluorination takes place with replacement of the alpha hydrogen by fluorine, The much weaker oxidant (PhSO2)(2)N-F reacts with PEN or DMPO in dichloromethane giving both the fluoro adduct and an adduct formally derived from an N-centred radical, assigned the structure of PhSO2N(F)PBN. or (PhSO2)(2)N-DMPO., respectively, This type of reaction proceeds by a version of the Forrester-Hepburn mechanism, in which an acid HA, in this case HF, initially adds to the nitrone function to give a hydroxylamine derivative which is oxidized by (PhSO2)N-F giving the fluoro spin adduct, a proton and the highly labile radical anion (PhSO2)(2)N-F.-. By decomposition of the latter to PhSO2(F)N- and PhSO2., conditions are set up for propagation of the reaction by a new molecule of HA [now PhSO2(F)NH] and thus formation of the PhSO2(F)N spin adduct.