A practical and mild chlorination of fused heterocyclic N-oxides

Fused azine N-oxides were selectively chlorinated at C2 in moderate to excellent yields, employing Vilsmeier reagent as both the activating agent and the nucleophilic chloride source. Remarkable features of the method include simple operation, mild reaction conditions, a wide substrate scope, and the use of only stoichiometric amount of POCl3. The potential extension of this method to a one-pot oxidation/chlorination sequence that obviates the need for isolation of the N-oxide intermediates is also validated.