Facile, high-yield, regioselective synthesis of ortho-nitro derivatives of hydroxy heterocycles using cerium (IV) ammonium nitrate

A series of hydroxy heterocycles with two different unsubstituted ortho sites undergo exclusive regioselective nitration with the CAN/NaHCO 3 reagent at the less hindered ortho site.Neither dinitro nor oxidized products were observed.The hydroxy heterocycles studied include: some derivatives of 7-hydroxycoumarins, sesamol, 2,3-dihydrobenzo[b]furan-3-one, 6-hydroxy-1,3benzoxathiol, 5-hydroxybenzothiazol, 5-hydroxyindole, 7-benzofuranol, and(5isoxazolyl)phenols. A mechanism is proposed in which an initial oxidation of the phenol to a radical cation by CAN occurs.Another molecule of CAN subsequently reacts with the phenolic radical cation to give an radical adduct from which an NO 2 radical is transferred to the less hindered carbon via a tight ion-radical pair yielding the Wheland complex that furnishes the nitrophenol after proton loss.