27.1 Preparation of 9-benzyl-2,6-dichloro-9H-purine
Potassium carbonate (2.07 g, 15 mmol) was added to a solution of 2,6-dichloro-9H-purine (945 mg, 5.0 mmol) in dimethylformamide (20 mL) and the mixture was stirred at room temperature for 30 minutes. Benzyl bromide (1.2 mL, 10 mmol) was then added and the mixture was stirred overnight. Upon completion of the reaction, water was added and the resulting mixture was extracted with ethyl acetate. The organic extracts were combined, washed sequentially with water and brine, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. Purification of the residue by rapid chromatography on silica gel column (Presearch Combiflash Rf) with ethyl acetate/hexane (0% to 80% gradient) as eluent gave 9-benzyl-2,6-dichloro-9H-purine as a white solid. The compound was characterized by the following data: 1H NMR (400 MHz, CDCl3) δ 8.10 (1H, s), 7.40 (5H, m), 5.40 (2H, s) ppm.
27.2 Preparation of 9-benzyl-2-chloro-6-trimethylmethylstannyl-9H-purine
