To a 1M solution of 3-(4-methoxybenzyl)-6,7,8,9-tetrahydro-3H-pyrazolo[3,4-c][2,7]naphthyridine (0.84 g, 2.88 mmol) in anhydrous THF was added dropwise triphosgene (1.28 g, 4.32 mmol) and triethylamine (0.92 mL, 6.62 mmol). The reaction mixture was stirred at room temperature for 16 hours. The solvent was then removed under reduced pressure to give the desired product, 3-(4-methoxybenzyl)-8,9-dihydro-3H-pyrazolo[3,4-c][2,7]naphthyridine-7(6H)-carbonyl chloride as an orange solid was used immediately in the next step without any further purification.
