Synthesis of two novel pyridine annulated pyrrolidine nitroxides

Two novel, unsubstituted, pyridine-annulated pyrrolidine nitroxides; 1,1,3,3-tetramethyl-2,3-dihydro-1H-pyrrolo[3,4-c]pyridin-2-yloxyl and 1,1,3,3-tetramethyl-2,3-dihydro-1H-pyrrolo[3,4-c]pyridin-5-oxide-2-yloxyl were synthesized in overall yield of ~15% (5 steps starting from pyridine-3,4-dicarboxyic acid) via a Grignard approach. Grignard methylation of N-benzylcinchomeronic imide that was derived from pyridine-3,4-dicarboxylic anhydride, furnished the tetramethylpyrrolidine precursor in an isolated yield of 18%. Hydrogenation of the tetramethyl pyrrolidine precursor followed by oxidation afforded, depending on the oxidation conditions, each of the two nitroxides.