2,3,5,6,7,8-Hexahydrophthalazine-1,4-dione (40) (2.09 g, 12.6 mmol) was used as a starting material, which was suspended in phosphorus trichloride (POCl3, 10 mL) and heated to reflux for 1 hour. After completion of the reaction, it was cooled to room temperature and the reaction mixture was slowly poured into ice water. The precipitated solid product was collected by filtration and dried in a vacuum oven to afford 1,4-dichloro-5,6,7,8-tetrahydro-2,3-diazanaphthalene (41) (2.23 g, 87% yield). The molecular ion peak (MH+) was determined as 203.0139 by high resolution mass spectrometry (HR MS).
