According to Scheme 2 Step 3: To a stirred solution of 4-(4-chlorobenzyl)-6-bromo-1,2,4-triazine-3,5(2H,4H)-dione (0.400 g) and 2(B) (411 mg, 1.3 mmol) in DMF (5 mL) were successively added of the 3-acetamidophenylboronic acid (0.34 g, 1.9 mmol), copper(II) acetate (0.23 g, 1.3 mmol) and 0.20 g of pyridine (2.5 mmol). The mixture was stirred overnight at 60° C. The reaction mixture was quenched with a saturated sodium bicarbonate solution and extracted with ethyl acetate (×3). The combined organic layers were washed successively with water, brine, dried over MgSO4, filtered and concentrated. The crude product was purified by C18 reverse phase column, 65 g column: 20% CH3CN gradient 20 to 60% to afford 0.350 g (yield=62%) of N-(3-(4-(4-chlorobenzyl)-6-bromo-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide 2(C).
