ABSTRACT
N-oxides form stable salts by reaction with acids and are converted by the appropriate halides to the corresponding N-alkoxy as well as the N-acyloxy and N-sulfonyloxy pyridinium salts. Addition of a dipolarophile to the nitrone function in heterocyclic N-oxides leads to a similar intermediate. Heterocyclic N-oxides readily form salts with protic acids. These are usually crystalline materials, which can be used for purification purposes. As might be expected, heterocyclic N-oxides easily enter in SN2 reactions with positively charged carbon atoms, and treatment with alkyl halides, sulfates, or sulfonates yields the corresponding N-alkoxy quaternary salts. One of the first reported observations about heterocyclic N-oxides is their enhanced stability towards deoxygenation with respect to aliphatic amine N-oxides. Phosphorus derivatives probably form the most consistently used class of reagents for the N-deoxygenation of heterocyclic derivatives.
