TPAP/NMO System as a Novel Method for the Synthesis of Nitronyl Nitroxide Radicals

Abstract

An easy oxidation of dihydroxyimidazolidine derivatives to nitronyl nitroxide radicals (NNRs) can be achieved using the tetra-N-propylamonium perruthenate/N-methylmorpholine N-oxide (TPAP/NMO) system. The procedure offers several advantages in terms of simplicity, yield, cost and ‘green’ chemistry.

Key words

radicals - oxidations - nitronyl nitroxide - green chemistry - TPAP/NMO

References and Notes

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14

To a solution of 4-(1,3-dihydroxy-4,4,5,5-tetramethyl-indolizidin-2-yl)benzoic acid methyl ester (1a, 73 mg, 0.25 mmol) in CH₂Cl₂ (3 mL), TPAP (0.05 equiv) and NMO (1 equiv) were added in sequence and the reaction mixture left at r.t. under stirring until the complete disappearance of the starting material monitored by TLC. After 3 h the crude was washed with H₂O, evaporated to dryness and purified by silica gel column chromatography, using Et₂O as eluent. Compound 2a was obtained as a blue powder (59 mg, 81% yield), characterized by EPR and elemental analysis.