methyl (3-amino-4-fluoro-5-(piperazin-1-yl)phenyl)(4-methoxybenzyl)carbamate (470 mg, 0.605 mmol) (crude product from above, contains DCE and TFA) was dissolved in methanol (5 ml)+Tetrahydrofuran (5 ml). oxetan-3-one (0.15 ml, 2.56 mmol), Trimethyl orthoformate (1 ml, 9.05 mmol) and potassium acetate (119 mg, 1.210 mmol) were added and the mixture stirred at room temperature for 15 minutes. pH was checked to be ˜4.5. Sodium cyanoborohydride (160 mg, 2.55 mmol) was added and stirring at room temperature continued for 20 hours. The reaction mixture was partitioned between EtOAc and dilutes aq. NaHCO3 solution. The organic layer was washed with brine, then dried over MgSO4 and evaporated to dryness to give crude methyl (3-amino-4-fluoro-5-(4-(oxetan-3-yl)piperazin-1-yl)phenyl)(4-methoxybenzyl)carbamate (248.4 mg) which was used without further purification.
