Synthesis of 4-(2-chlorophenyl)-1, 6-dihydro-1, 3, 9-trimethylimidazo[1, 2-a]pyrazolo[4, 3-f] [1, 4]diazepine-9-14C (CI-918-14C)

4-(2-Chlorophenyl)-1, 6-dihydro-1,3,9-trimethylimidazo[1,2-a]pyrazolo-[4,3-f] [1,4]diazepine-9-14C (CI-918-14C) was made starting with acetyl-1-14C chloride. An efficient synthesis of 1-chloro-2-propanone-2-14C was developed as a precursor to 2-methyl-1,3-dioxolane-2-14C-2-methanamine. The latter reacted with 4-(2-chlorophenyl)-1,6-dihydro-1,3-dimethylpyrazolo[3,4-e] [1,4]diazepine-7-thione to yield 4-(2-chlorophenyl)-1,6-dihydro-1, 3-dimethyl-N-[(2-methyl-1,3-dioxolan-2-yl-2-14C)methyl] pyrazolo[3,4-e] [1,4]diazepin-7-amine. Hydrolysis and cyclization gave the title compound. The six-step reaction sequence gave an overall radiochemical yield of 19%. The product had a specific activity of 8.31 mCi/mmol.