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To a solution of (2-tert-butoxy-2-oxoethyl)zinc(II) chloride (0.5M in Et2O; 670 ml, 335 mmol) at 0° C. was added drop wise a solution of 7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-one (55 g, 167 mmol) in THF (30 mL). The resulting reaction mixture was stirred at 0° C. for 1 h. The reaction mixture was quenched with aqueous, saturated NH4Cl solution and extracted with EtOAc. The organic extracts were dried over Na2SO4 and concentrated under reduced pressure to afford tert-butyl 2-(7-bromo-3-chloro-1-fluoro-5-hydroxy-5H-chromeno[2,3-c]pyridin-5-yl)acetate (66.0 g, 148 mmol, 89% yield) as a yellow solid. Step 2: A solution of tert-butyl 2-(7-bromo-3-chloro-1-fluoro-5-hydroxy-5H-chromeno[2,3-c]pyridin-5-yl)acetate (66 g, 148 mmol) in THF (200 mL) was cooled to −78° C. followed by the drop wise addition of diisobutylaluminum hydride (1.0 M solution in THF; 180 ml, 180 mmol). The resulting reaction mixture was cooled to 0° C. and stirred for 2 h. The reaction mixture was quenched with aqueous, saturated NH4Cl solutionand extracted with EtOAc. The combined organics were dried over Na2SO4 and concentrated under reduced pressure. The obtained residue was purified by chromatography (0-50% EtOAc/hexanes) to afford 7-bromo-3-chloro-1-fluoro-5-(2-hydroxyethyl)-5H-chromeno[2,3-c]pyridin-5-ol (48 g, 128 mmol, 86% yield) as a light yellow solid. Step 3: To a solution of 7-bromo-3-chloro-1-fluoro-5-(2-hydroxyethyl)-5H-chromeno[2,3-c]pyridin-5-ol (48 g, 128 mmol) in THF (58 mL) were added azidotrimethylsilane (34.0 ml, 256 mmol) and boron trifluoride diethyl etherate (31.6 ml, 256 mmol). The reaction mixture was heated to 60° C. for 15 h. Additional azidotrimethylsilane (34.0 ml, 256 mmol) and boron trifluoride diethyl etherate (31.6 ml, 256 mmol) were added and heating was continued for 3 h. The reaction mixture was quenched with aqueous, saturated NaHCO3 solution and extracted with EtOAc. The organic phase was separated, dried over Na2SO4 and concentrated under reduced pressure. The residue was purified by chromatography (0-30% EtOAc/hexanes) to afford 2-(5-azido-7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)ethanol (41 g, 103 mmol, 80% yield) as a pale yellow solid-foam. Step 4: To a solution of LAH (1.0 M solution in tetrahydrafuran; 90 ml, 90 mmol) in THF (50 mL) at rt was added drop wise a solution of 2-(5-azido-7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)ethanol (24 g, 60.1 mmol) in THF (150 mL). The resulting mixture was stirred at RT for 1 h. The reaction mixture was quenched with sodiumsulfate decahydrate and stirred for 30 min. The mixture was filtered, the filtrate was concentrated under reduced pressure and the residue was purified by chromatography (0-50% EtOAc/hexanes) to afford 2-(5-amino-7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)ethanol (16.5 g, 44.2 mmol) as a colorless oil. Step 5: To a solution of 2-(5-amino-7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)ethanol (13 g, 34.8 mmol) in EtOH (50 mL) was added sodium acetate (5.71 g, 69.6 mmol) followed by the dropwise addition of cyanogen bromide (3.0M solution in DCM; 13.92 ml, 41.8 mmol). The resulting mixture was stirred at RT for 5 days. The reaction mixture was concentrated under reduced pressure, washed with water extracted with DCM. The combined organic layers were dried over Na2SO4, concentrated under reduced pressure and azeotropically dried with toluene. The obtained residue was dissolved in DCM and TFA (40 mL) was added to the solution. The resulting mixture was stirred at RT for 30 min. The mixture was carefully quenched with aqueous, saturated NaHCO3 solution and extracted with DCM. The combined organics were dried over Na2SO4 and concentrated under reduced pressure. The obtained residue was purified by chromatogrpahy (0-3% MeOH/DCM) to afford 7-bromo-3-chloro-1-fluoro-5′,6′-dihydrospiro[chromeno[2,3-c]pyridine-5,4′-[1,3]oxazin]-2′-amine (6.2 g, 15.55 mmol, 44.7% yield) as a light yellow solid. Step 6: Intermediates (R)-7-bromo-3-chloro-1-fluoro-5′,6′-dihydrospiro[chromeno[2,3-c]pyridine-5,4′-[1,3]oxazin]-2′-amine (15A) and (S)-7-bromo-3-chloro-1-fluoro-5′,6′-dihydrospiro[chromeno[2,3-c]pyridine-5,4′-[1,3]oxazin]-2′-amine (15B) were obtained from racemic 7-bromo-3-chloro-1-fluoro-5′,6′-dihydrospiro[chromeno[2,3-c]pyridine-5,4′-[1,3]oxazin]-2′-amine using similar chiral separation conditions as described herein for intermediate 10.

1. customThe resulting reaction mixture
2. customThe reaction mixture was quenched with aqueous, saturated NH4Cl solution
3. extractionextracted with EtOAc
4. dry with materialThe organic extracts were dried over Na2SO4
5. concentrationconcentrated under reduced pressure