ABSTRACT
Reaction of heterocycles with anhydrous percarboxylic acids, often at room temperature or slightly above, smoothly produces the corresponding N-oxides. The azo group is somewhat less readily oxidized than a ring nitrogen, and both azo- and azoxy-N-oxides are obtained from phenylazopyridines. A large variety of heterocyclic N-oxides have been obtained from derivatives of hydroxylamine, and most of the syntheses employed reproduce the well-known pathways for the synthesis of the corresponding nonoxidized heterocycles from ammonia derivatives. The reaction between the amide and the oxime functions leads to the N-oxides of 1,3-diaza heterocycles, exemplified by the synthesis of the imidazole ring from the oxime of N-acyl-N-phenyl-2-amino-2-propanone. The easily available aromatic nitro derivatives are an attractive starting material for the syntheses, and most heterocyclic N-oxides prepared in this way contain a fused carbo- or hetero-cyclic ring. Nitro groups in the side chain analogously undergo reduction and cyclization, e.g., an isoquinoline derivative is obtained from 2-(2'-nitroacetyl)benzoic acid on treatment with SnCl2.
