Formation of 1,2,4-oxadiazoles in the course of photooxidation of aromatic azides in acetonitrile

Photolysis of aryl azides at room temperature in acetonitrile in the presence of oxygen proceeds as arene ring opening and acetonitrile trapping to afford 5-methyl-3-(5-oxopenta-1,3-dien-1-yl)-1,2,4-oxadiazoles. In the case of 4-methoxyphenyl azide, a product depriving of acetonitrile reactant, 1-hydroxyimino-3-methylcyclopentadiene-2-carbaldehyde, is also formed.