Synthesis of carbon‐13 and carbon‐14 labelled triazolo‐1,4‐benzodiazepines

Abstract
An efficient two‐step synthesis of 8‐chloro‐1‐methyl‐6‐phenyl‐[3H]‐S‐triazolo‐[4,3‐a][1,4]‐benzodiazepine (alprazolam) and 8‐chloro‐6‐(2‐chlorophenyl)‐1‐methyl‐[3H]‐S‐triazolo‐[4,3‐a][1,4]‐benzodiazepine (triazolam) labelled with carbon‐13 or carbon‐14 from their corresponding hydrazines is reported. The method involves acylation of the appropriate hydrazine using the mixed carbonic anhydride of sodium [13C] or [14C] acetate and isobutylchloroformate under mild conditions. Thermolysis of the resulting acetylhydrazides gave the target carbon‐14 and carbon‐13 labelled compounds in good yields.