Potassium Carbonate → 2,3-Bis(p-methoxyphenyl)-5-chloropyrazine
Reaktionsgleichung
[CH3:1][O:2][C:3]1[CH:8]=[CH:7][C:6]([C:9]2[C:14]([C:15]3[CH:20]=[CH:19][C:18]([O:21][CH3:22])=[CH:17][CH:16]=3)=[N:13][CH:12]=[CH:11][N+:10]=2[O-])=[CH:5][CH:4]=1.C(=O)([O-])[O-].[K+].[K+].P(Cl)(Cl)([Cl:32])=O>>[CH3:1][O:2][C:3]1[CH:8]=[CH:7][C:6]([C:9]2[C:14]([C:15]3[CH:20]=[CH:19][C:18]([O:21][CH3:22])=[CH:17][CH:16]=3)=[N:13][C:12]([Cl:32])=[CH:11][N:10]=2)=[CH:5][CH:4]=1Komponenten
4
Versuchsvorschrift
To 20 ml of phosphorus oxychloride was added with stirring 3.918 g of 2,3-bis(p-methoxyphenyl)pyrazine oxide. The mixture was heated under reflux for 30 minutes. After allowed to cool, the reaction mixture was poured into ice water and then made basic with potassium carbonate to precipitate the product, which was collected by filtration. There was obtained 2.823 g of 2,3-bis(p-methoxyphenyl)-5-chloropyrazine. A mixture of 653 mg of said compound, 414 mg of anhydrous potassium carbonate and 116 mg of tetrakis(triphenylphosphine)palladium was suspended in an atmosphere of argon in 10 ml of dry N,N-dimethylformamide. To the suspension was added 2 ml of a hexane solution of triethylborane (15%). The resulting mixture was heated under reflux for 2 hours, followed by removal of the solvent by distillation under reduced pressure. Water was added to the residue, and the resulting mixture was extracted three times with methylene chloride. The organic layer from the extraction was washed with water and dried over anhydrous sodium sulfate. Removal of the solvent by distillation under reduced pressure afforded 850 mg of an extraction residue. The residue was subjected to column chromatography on silica gel. There was obtained 555 mg of 2,3-bis(p-methoxyphenyl)-5-ethylpyrazine from the eluates with a 1:1 hexane:methylene chloride mixture. M.P. 76.5°-78° C. (colorless needles, recrystallized from ethanol). Physical properties of the product support a chemical structure of the below formula (XII).