反应详情

Potassium carbonate (270 mg, 1.95 mmol) and methyl iodide (78 μl, 1.27 mmol) is added at room temperature to a solution of 1-bromo-7,8-dimethoxy-3H-pyrazolo[3,4-c]quinoline (300 mg, 972 μmol) in anhydrous N,N-dimethylformamide (36 ml). The reaction mixture is subsequently stirred at room temperature for 18 h. When the reaction is complete, the mixture is poured into water (150 ml) and diluted with ethyl acetate (150 ml). The phases are separated, and the aqueous phase is extracted a number of times with ethyl acetate. The combined organic phases are dried over Na2SO4, filtered with suction, and the filtrate is evaporated to dryness in vacuo, giving 282 mg (876 μmol) of a mixture of the title compound (Rf=0.45) and 1-bromo-7,8-dimethoxy-2-methyl-2H-pyrazolo[3,4-c]quinoline (Rf=0.55) in the mixing ratio 3:1. For purification, the regioisomer mixture is dissolved in hot ethyl acetate in such a way that a minimal volume of solvent is sufficient for complete dissolution. The solution is subsequently slowly cooled to 0° C., giving a precipitate of pure 1-bromo-7,8-dimethoxy-3-methyl-3H-pyrazolo[3,4-c]quinoline (125 mg). After filtration with suction, the filtrate (regioisomer mixture about 1:1), evaporated in vacuo, is again dissolved in hot ethyl acetate, and a little cyclohexane is added to the solution. After 24 h, the precipitate obtained is filtered off with suction, giving further 1-bromo-7,8-dimethoxy-3-methyl-3H-pyrazolo[3,4-c]-quinoline (31 mg). The combined crystal batches are dried in a high vacuum, giving the title compound 1-bromo-7,8-dimethoxy-3-methyl-3H-pyrazolo[3,4-c]quinoline (156 mg, 484 μmol) having a melting point of 235.5° C. MS: 322.0/324.0 (M+H+, monobromo isotope distribution), TLC (HPTLC): Rf=0.45 (ethyl acetate/ethanol 8:1, parts by volume).

1. customThe phases are separated
2. extractionthe aqueous phase is extracted a number of times with ethyl acetate
3. dry with materialThe combined organic phases are dried over Na2SO4
4. filtrationfiltered with suction
5. customthe filtrate is evaporated to dryness in vacuo