A solution of 4-[(2,4-dichlorophenyl)carbonyl]-2-piperazinone (I6) (0.273 g, 1 mmol) in dry Dichloromethane (DCM) (3 ml) was stirred at room temperature under argon. Triethyloxonium tetrafluoroborate (0.199 g, 1.050 mmol) was added and the reaction solution was stirred for 10 minutes. 2-pyrazinecarbohydrazide (0.166 g, 1.200 mmol, commercially available) was then added and the solution was stirred for a further 1 hour. The solvent was then concentrated before n-butanol (3.00 ml) was added and the solution was stirred, under reflux and argon, for 4 hours. LCMS confirmed product location, thus the solution was cooled to room temperature before the solvent was evaporated in vacuo. The remaining residue was then purified by flash chromatograpghy (Biotage SP4, 25M cartridge) with a gradient of 0 to 10% 2M NH3/MeOH in DCM. TLC confirmed product location and the solvent from the combined fractions was evaporated in vacuo. The remaining residue was then further purified by mass-directed automated HPLC. The solvent was then evaporated in vacuo, and the remaining solid was triturated with ether, and dried in a vacuum oven to yield the product in 0.137 g.
