Abstract A very efficient synthesis of the unknown family of 6, 7-dihydro [1, 2, 3] triazolo [1, 5- a] pyridines from [1, 2, 3] triazolo [1, 5-a] pyridines have been developed, and a mechanism for their formation has been proposed. Their behaviour with NBS to give 4, 5-dibromo substituted-4, 5, 6, 7-tetrahydro-[1, 2, 3] triazolo [1, 5-a] pyridines is studied.[ABSTRACT FROM AUTHOR]