[Cl:1][C:2]1[N:3]=[C:4]([Cl:11])[C:5]2[NH:10][CH:9]=[CH:8][C:6]=2[N:7]=1.[CH3:12]OS(C)(=O)=O.C(=O)([O-])[O-].[Cs+].[Cs+]>CN(C)C=O.C(OCC)(=O)C>[Cl:1][C:2]1[N:3]=[C:4]([Cl:11])[C:5]2[N:10]([CH3:12])[CH:9]=[CH:8][C:6]=2[N:7]=1A mixture of 2,4-dichloro-5H-pyrrolo[3,2-d]pyrimidine (2.67 g, 14.2 mmol), methanesulfonic acid methyl ester (1.26 mL, 14.9 mmol) and cesium carbonate (9.25 g, 28.4 mmol) in anhydrous N,N-dimethylformamide (21 mL) was stirred at RT (room temperature) under N2 for 15 h. The reaction mixture was diluted with ethyl acetate, and the organic layer was washed with 1:1 water/brine (3×) and brine (1×), dried over Na2SO4, filtered, and concentrated in vacuo. The crude product was purified by silica gel chromatography to give 2.50 g (87.1%) of 2,4-dichloro-5-methyl-5H-pyrrolo[3,2-d]pyrimidine as a white solid. MS(ESI) m/z: 202.2/204.1 [M+1]+.
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