ESR of new beta-phosphorus nitroxides from aldo- and keto-nitrones

This investigation deals mainly with the synthesis of new phosphorus-nitrox ide free radicals. Nitroxides with a beta -(31) P group were synthesized fr om the aldo-nitrones alpha-phenyl-N-tert-butylnitrone and 5,5-dimethyl-1-py rroline-N-oxide (DMPO) as well as the keto-nitrones 2,5,5-trimethyl-1-pyrro line-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 involv ed nitronyl spin trapping of phosphorus-centred radicals generated thermall y 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 t he strong, hindered base lithium diisopropylamide) to the nitrones and subs equent one-electron oxidation to the corresponding nitroxides. The most nov el feature of the work presented here may be the synthesis of beta-phosphor anyl [P(OR)(4)] nitroxide spin adducts. For comparison purposes the related beta-phosphityl [P(O)(OR)(2)] nitroxides were also assembled and character ized by ESR spectroscopy. Copyright (C) 1999 John Wiley & Sons, Ltd.