CCOC(/N=N/C(OCC)=O)=O.[Cl:13][C:14]1[N:22]=[C:21]2[C:17]([NH:18][CH:19]=[N:20]2)=[C:16]([Cl:23])[N:15]=1.[C:24]1(P(C2C=CC=CC=2)C2C=CC=CC=2)[CH:29]=CC=C[CH:25]=1.C(O)(C)C>C1COCC1>[Cl:13][C:14]1[N:22]=[C:21]2[C:17]([N:18]=[CH:19][N:20]2[CH:24]([CH3:29])[CH3:25])=[C:16]([Cl:23])[N:15]=1
Add DEAD (4.7 g, 27.09 mmol) slowly to a solution of 2,6-dichloropurine (1, 5 g, 26.5 mmol), triphenylphosphine (1 1.75 g, 44.5 mmol) and isopropyl alcohol (2b, 10 ml) in THF (100 ml), and stir at room temperature for 24 hours. Concentrate the reaction mixture, dissolve the residue in DCM (20 ml) and filter to remove the unwanted solids. Load the filtrate onto a 90 gram silica gel column (Biotage), and elute with DCM/acetone (95:5). Concentrate the desired fractions to give 3.0 grams of 2,6-dichloro-9-isopropyl-9H-purine (3b). 1H-NMR (CDCl3): δ 8.2(s, 1H), 4.95 (pentet, 1H), 1.63 (d, 6H)
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