To a cold (0° C.) solution of Example 3A (200 mg, 0.661 mmol) in dichloromethane (2.2 mL) was added meta-chloroperoxybenzoic acid (179 mg, 0.728 mmol) in a single portion. After 1 hour, the reaction mixture was partitioned between 10% sodium thiosulfate solution and ethyl acetate. The layers were separated, and the organic layer was washed with saturated sodium bicarbonate solution, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was dissolved in N,N-dimethylformamide (3 mL). Hunig's base (231 μl, 1.323 mmol) and 4-(4-methylpiperazin-1-yl)aniline (127 mg, 0.661 mmol) were added to the solution, and the reaction was heated to 45° C. for 3 hours.
