A facile synthesis of 1,2,4-triazine fused pyrroline nitroxides as useful paramagnetic building block

In this study, we report an efficient synthesis of 3-amino- or 3-methylsulfanyl-6-oxyl-pyrrolo[3,4-e][1,2,4] triazine radical from O -methyl protected 3,4-dioxopyrrolidine pre-nitroxide. From the amino derivative, the corresponding 3-iodo-6-oxyl-pyrrolo[3,4-e][1,2,4]triazine radical was obtained via radical substitution. This compound was an excellent substrate for Pd-catalyzed cross-coupling reactions. The oxidation of O -methyl protected 3-methylsulfanyl-pyrrolo[3,4-e][1,2,4]triazine with excess amount of 3-chloroperbenzoic acid afforded a 3-methylsulfonyl-6-oxyl-pyrrolo[3,4-e][1,2,4]triazine radical that could be used in aromatic nucleophilic substitution reactions to produce new paramagnetically modified amino acids and polycyclic compounds via an intramolecular Diels-Alder reaction.