3H-[1, 2, 4] thiadiazolo [4, 3-a] pyridines. The reaction involved 2- trichloromethylthioaminopyridine (1) as an intermediate and, under carefully controlled reaction conditions, 1 was isolated in a pure and relatively stable state. 3 This present communication deals with the use of this trichloro compound in the synthesis of 3H-[1, 2, 4] thiadiazolo [4, 3-a] pyridines with a variety of substituents in the 3 position.