[CH3:1][C:2]1[CH:7]=[CH:6][N:5]2[N:8]=[N:9][N:10]=[C:4]2[CH:3]=1.[Br:11]N1C(=O)CCC1=O.C1C=CC=CC=1.BrN1C(=O)CCC1=O>C1C=CC=CC=1.C(OOC(=O)C1C=CC=CC=1)(=O)C1C=CC=CC=1>[Br:11][CH2:1][C:2]1[CH:7]=[CH:6][N:5]2[N:8]=[N:9][N:10]=[C:4]2[CH:3]=17-Methyl tetrazolo [1,5-a]pyridine [Boyer, et al., J. Am. Chem. Soc., 82, 2218 (1960] (23 g. 173 mmole), benzene N-bromosuccinimide (30.6 g. 173 mmole) and benzoyl peroxide (100 mg) in 1.5 liters of benzene is refluxed overnight. More N-bromosuccinimide (15.3 g. 86.5 mole) is added and the reflux is maintained for several hours. The mixture is cooled and washed with 100 ml 20% sodium hydroxide and then with water. It is dried over calcium chloride, evaporated to dryness to yield 36.4 g of a mixture of 7-bromomethyltetrazolo [1,5-a]pyridine (63%) 7-dibromomethyltetrazolo [1,5-a]pyridine (24%) and 7-methyltetrazolo [1,5-a]pyridine (13%). Two triturations of this mixture with 500 ml of ether-hexane 1:1 (v/v) affords 25 g of a mixture consisting of 82% monobromo derivative, 13% dibromo derivative and 5% of starting material. This mixture is used for the next step.
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