Thermolysis of the reaction products from 2‐pyridylacetohydrazide and nitrous acid

2,3‐Dihydroimidazo[1,5‐α]pyridin‐3‐one (IV) was obtained by thermolysis of 2‐pyridylacetyl azide (II) which was prepared from 2‐pyridylacetohydrazide (I) on treatment with an equivalent mole of nitrous acid. Treatment of I with excess nitrous acid yielded α‐oximino‐α:‐(2‐pyridyl)‐acetylazide (V). Thermal decomposition of V gave 3‐(2‐pyridyl)‐1,2,4‐4 H ‐oxadiazolin‐5‐one (VII). 2‐Cyanopyridine (IX) was obtained from V by the action of alkali. 2,3‐Dihydroimidazo‐[1,5‐α ]pyridin‐3‐one (IV) was rearranged to VII upon treatment with nitrous acid. J. Chem. Soc. , 14, 993 (1977)