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EXAMPLE 3A; 6,7-dimethoxyquinoxaline-2,3(lH,4H)-dione; A mixture of 4,5-dimethoxybenzene-l,2-diamine (9 g, 53.5 mmol) and oxalic acid (9.64 g, 107 mmol) in 3 N aqueous HCl (100 mL) was heated at reflux for 4 hours. The mixture was cooled and filtered, the solid was washed with copious amount of water, and dried under vacuum at 50C overnight to afford the title compound. NMR (300 MHz, dimethylsulfoxide-de) delta 11.73 (s, 2 H) 6.72 (s, 2 H) 3.34 (s, 6 H). MS ESI(+) m/z 222.9 (M+H)+.
palladium-carbon; In hydrogenchloride; ethyl acetate;
6,7-Dimethoxy-1,4-dihydroquinoxaline-2,3-dione (10). 4,5-Dimethoxy-1,2-dinitrobenzene 8 (912 mg, 4.00 mmol) was dissolved in ethyl acetate (30 mL). To this solution was added 10% Pd/C (228 mg, 20%; Aldrich). The mixture was then stirred at room temperature under a pressure of 40 psi (H2) for 14 hr. The catalyst was removed through a column of Celite (5 g) and washed with ethyl acetate (3*15 mL) under nitrogen. The filtrates were combined and the solvent was removed to give the diamine 9 as a nearly colorless solid. The 1 H NMR spectrum was consistent with the assigned structure. Diamine 9 was dissolved in 4N hydrochloric acid (7 mL), and <strong>[6153-56-6]<strong>[6153-56-6]oxalic acid</strong> dihydrate</strong> (504 mg, 4.00 mmol; Fisher) was added to this solution in one portion with stirring under N2. The mixture was refluxed at 130-5 C. (oil bath) for 3 hr. A yellow solid precipitated, which was collected by suction filtration and dried in vacuo overnight, giving 725 mg (82% based on compound 8) of the title compound as a pale yellow solid; mp 345-346 C.; 1 H NMR (CDCl3, 300 MHz) delta3.677 (s, 3H), 6.681 (s, 2H), 11.695 (s, 2H). EIMS m/e 222 (100, M+).
3.B
EXAMPLE 3B; 2,3-dibromo-6,7-dimethoxyquinoxaline; In a 100 mL round-bottomed flask was placed EXAMPLE 3A (3.25 g, 14.63 mmol) and phosphorus pentabromide (12.59 g, 29.3 mmol) and this mixture was heated at 155°C for 1.5 hours. The mixture was then treated with ice- water and the solid was collected by filtration, and air-dried to afford the title compound. NMR (300 MHz, CDC13) δ ppm 7.29 (s, 2 H) 4.04 (s, 6 H). MS-MS ESI(+) m/z 220.0 (M+H)+.
With triethylamine; trichlorophosphate for 18h; Reflux;
4.1 Step 1: Preparation of 2,3-dichloro-6,7-dimethoxy-quinoxaline
6,7-dimethoxy-1,4-dihydro-quinoxaline-2,3-dione (6.5 g, 29.3 mmol)And triethylamine (6.1 ml, 44.0 mmol) were refluxed and stirred in 70 ml of POCl3 for 18 hours.After completion of the reaction, the reaction was terminated slowly with a methanol: water = 1: 1 solution while taking care of the heat, and the resulting solid was filtered and vacuum dried to obtain 4.9 g (65% yield) of the desired compound
65%
With triethylamine; trichlorophosphate for 18h; Reflux;
5.1 Step 1: Preparation of 2,3-dichloro-6,7-dimethoxy-quinoxaline
6,7-Dimethoxy-1,4-dihydro-quinoxaline-2,3-dione (6.5 g, 29.3 mmol) and triethylamine (6.1 ml, 44.0 mmol) were reflux stirred in 70 ml of POCl 3 for 18 hours. The reaction was slowly terminated using methanol:water mixture (1:1) carefully not to induce exothermic reaction. At this time, the resulting solid was filtered and vacuum dried. As a result, 4.9 g of a target compound was obtained (65% yield). Mass (M+H +): 260.0 1H NMR (500 MHz, DMSO-d6): δ3.94 (s, 6H), 7.42 (s, 2H).
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