To a suspension of 4-benzyloxy-2(1H)-pyridone (21.5 g), 6-bromo-1,2-dimethyl-1H-benzo[d]imidazole (16 g), N,N′-dimethylethylenediamine (7.57 ml) and potassium carbonate (29.5 g) in DMSO (160 ml) was added CuI (13.5 g), and the mixture was stirred at 90° C. for 5 h under Ar atmosphere. After the mixture was cooled, 28% NH3 solution (160 ml) and water (160 ml) were added. The precipitate was collected by filtration, washed with water and diisopropyl ether successively, and dried to give a solid. The residue was purified by silica gel column chromatography (hexane/EtOAc then EtOAc/MeOH) to give the title compound (14.5 g) as an off-white solid.
