Facile, high-yield, regioselective synthesis of ortho-nitrophenols using cerium(IV) ammonium nitrate

Certain phenols possessing at least one unsubstituted ortho position have been found to undergo rapid, regioselective ortho nitration with CAN (cerium (IV) ammonium nitrate) in the presence of NaHCO3 at room temperature to yield o-nitrophenols in high yields. Substituents tolerating these nitration conditions ranged from the activating methoxy and methyl groups to the moderately deactivating Cl, Br, CHO and CO2Me groups. In contrast, phenols that contained a strongly deactivating group such as nitro or cyano or 2,6-disubstituted phenols were not nitrated by the CAN/NaHCO3 reagent. More complex nitrophenols such as 6-hydroxy-5-nitro-1,3-benzoxanthiol-2-one, 7-hydroxy-6-nitro-3,4,8-trimethylcoumarin, 6-hydroxy-5-flavanone, 1-(4-hydroxy-3-nitrophenyl)-1H-tetrazole-5-thiol, 2-(2-hydroxy-3-nitrophenyl) benzoxazole were also prepared in good yields by the CAN/NaHCO3 reagent.