C(=O)([O-])[O-].[Cs+].[Cs+].Br[CH2:8][CH2:9]Br.[Cl:11][C:12]1[N:20]=[C:19]2[C:15]([N:16]=[C:17]([C:21]([OH:24])([CH3:23])[CH3:22])[NH:18]2)=[C:14]([Cl:25])[N:13]=1>CN(C=O)C>[Cl:25][C:14]1[C:15]2[N:16]=[C:17]3[N:18]([CH2:8][CH2:9][O:24][C:21]3([CH3:23])[CH3:22])[C:19]=2[N:20]=[C:12]([Cl:11])[N:13]=1Cesium carbonate (9.3 g, 28.5 mmol) and 1,2-dibromoethane (4.1 mL, 47.6 mmol) were added to a solution of 2-(2,6-dichloro-9H-purin-8-yl)-propan-2-ol (3.3 g, 13.36 mmol) in DMF (100 mL) and the reaction mixture was heated at 100° C. for 2 h, then partitioned between water and ethyl acetate. The organic extract was separated and washed with brine, then dried (MgSO4) and concentrated in vacuo. The resulting residue was purified by column chromatography (SiO2, 0 to 10 to 20% ethyl acetate in cyclohexane) affording 1,3-Dichloro-8,8-dimethyl-5,6-dihydro-8H-7-oxa-2,4,4b,9-tetraaza-fluorene as a yellow solid (1.0 g, 27%). 1H NMR (400 MHz, CDCl3): δ 4.26 (2H, dd, J=6, 4 Hz), 4.19 (2H, dd, J=6, 4 Hz).
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