4,7-Dichloro-thieno[2,3-d]pyridazine

91533-21-0

699-89-8

The general procedure for the synthesis of 4,7-dichlorothieno[2,3-d]pyrazine from 5,6-dihydrothieno[2,3-D]pyridazine-4,7-dione was carried out as follows: a 250 mL round-bottomed flask was equipped with a stirrer and reflux condenser tube. To the flask was added 5,6-dihydrothieno[2,3-D]pyridazine-4,7-dione (2.5 g, 14.8 mmol), phosphorus trichloride (45 mL, 481 mmol), and pyridine (4.57 mL, 55 mmol), and heated and refluxed for 2.5 hours. After the reaction was completed, it was cooled to room temperature and the reaction solution was slowly poured into ice water. The mixture was separated and the aqueous phase was extracted with chloroform (4 x 75 mL). The organic phases were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the dark yellow solid product 4,7-dichlorothieno[2,3-d]pyrazine (Intermediate B; 1.5 g, 7.3 mmol; 49% yield). The product was characterized by the following data: melting point 260-263 °C; 1H NMR (DMSO-d6) δ 8.55 (d, J = 5.7 Hz, 1H), 7.80 (d, J = 5.7 Hz, 1H); ESI-MS (M + H)+ m/z = 206; TLC (hexane-ethyl acetate, 70:30) Rf = 0.56. For related literature see: Robba, M.; Bull. Soc. Chim. Fr.; 1967, 4220-4235.