Studies on v-triazoles. Part III. On the nitration of 9-oxo-1H,9H-benzopyrano[2,3-d]-v-triazole

The nitration of 9-oxo-1H,9H-benzopyrano[2,3-d]-v-triazole ( 1 ) leads not to the expected benzenoid substitution product 2 but to initial attack on the triazole moiety resulting in fission to 3-diazo-2-nitrimino-2H-[1]benzopyran-4-yl oxide ( 3 ). Mild hydrolysis of 3 results in cleavage of the nitrimine to give 3-diazo-2-oxo-2H-[1]benzopyran-4-yl oxide ( 4 ). Further nitration of 3 under more forcing conditions leads to the 6-nitro derivative of 3 which also undergoes facile hydrolysis to a diazocoumarin.