A novel route to spin-labeled dihydrooxepines and o-benzoquinones

A reaction of a lithiated derivative of 4,4,5,5-tetramethyl-3-oxido-4,5-dihydro-1H-imidazole 1-oxyl with 3,6-di-tert-butyl-o-benzoquinone at −80 °C predominantly gave spin-labeled dihydrooxepine via nucleophilic 1,2-addition of the paramagnetic carbanion to the CO group of the benzoquinone followed by insertion of the O atom into the ring. At lower temperatures, this reaction was accompanied by 1,4-addition of the organolithium compound to the benzoquinone followed by oxidation of the resulting adduct into spin-labeled o-benzoquinone. This “one pot” process is a novel approach to organic derivatives that can further be converted into di- and polyradicals combining nitronyl nitroxide and semiquinolate fragments.