ESR of newβ-phosphorus nitroxides from aldo- and keto-nitrones

This investigation deals mainly with the synthesis of new phosphorus–nitroxide free radicals. Nitroxides with a β-31P group were synthesized from the aldo-nitrones α-phenyl-N-tert-butylnitrone and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as well as the keto-nitrones 2,5,5-trimethyl-1-pyrroline-N-oxide (2,5,5-M3PO) and 2-phenyl-5,5-dimethyl-1-pyrroline-N-oxide (2-Ph-DMPO). Three different routes were explored. The first two routes involved nitronyl spin trapping of phosphorus-centred radicals generated thermally or photochemically by hydrogen abstraction by tert-butoxyl radicals from di-tert-butyl peroxyoxalate or from photoexcited benzophenone, respectively. The third approach used the addition of phosphorus anions (generated by the strong, hindered base lithium diisopropylamide) to the nitrones and subsequent one-electron oxidation to the corresponding nitroxides. The most novel feature of the work presented here may be the synthesis of β-phosphoranyl [P(OR)4] nitroxide spin adducts. For comparison purposes the related β-phosphityl [P(O)(OR)2] nitroxides were also assembled and characterized by ESR spectroscopy. Copyright © 1999 John Wiley & Sons, Ltd.