A suspension of 7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-one (20 g, 60.9 mmol), (R)-2-methyl-2-propanesulfinamide (14.76 g, 122 mmol), and titanium (IV) ethoxide (25.2 mL, 122 mmol) in THF (250 mL) was heated to 70° C. for 24 h. Additional (R)-2-methyl-2-propanesulfinamide (1.0 equiv) and titanium (IV) ethoxide (1.0 equiv) were added and the reaction mixture was heated for additional 24 h. Additional (R)-2-methyl-2-propanesulfinamide (1.0 equiv) and titanium (IV) ethoxide (1.0 equiv) were added and the reaction mixture was heated for additional 8 h. The reaction mixture was quenched with brine (150 mL). The resulting suspension was filtered through celite, and the filter cake was washed with EtOAc. The filtrate was washed with brine, dried over Na2SO4 and concentrated under reduced pressure. The residue was purified by chromatography (100% hexanes) to afford racemic N-(7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-ylidene)-2-methylpropane-2-sulfinamide as an orange solid (15 g, 34.7 mmol, 57.1% yield). Step 2: A solution of (2-tert-butoxy-2-oxoethyl)zinc(II) chloride (0.5M in Et2O; 116 mL, 57.9 mmol) was cooled to 0° C. and a solution of (Z)—N-(7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-ylidene)-2-methylpropane-2-sulfinamide (10 g, 23.16 mmol) in THF (100 mL) was added drop wise. The resulting mixture was stirred at for 1 hour 0° C. The reaction mixture was diluted with EtOAc and washed with aqueous saturated solution of NH4Cl, followed by brine. The organic layer was dried over Na2SO4, and concentrated under reduced pressure. The obtained residue was purified by chromatography (0-20% EtOAc/hexanes) to afford tert-butyl 2-(7-bromo-3-chloro-5-(1,1-dimethylethylsulfinamido)-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)acetate (7.5 g, 13.69 mmol, 59.1% yield) as a yellow solid. Step 3: A solution of tert-butyl 2-(7-bromo-3-chloro-5-(1,1-dimethylethylsulfinamido)-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)acetate (7.5 g, 13.69 mmol) in dry THF (25 mL) was cooled to −78° C. and diisobutylaluminum hydride (54.8 mL, 54.8 mmol) was added drop wise. The mixture was warmed to 0° C. and kept at this temperature for 1 h. The reaction mixture was quenched with a aqueous, saturated solution of Rochelle's salt and vigorously stirred for 15 h. The organic layer was separated and the aqueous phase was extracted with EtOAc. The combined organic layers were washed with brine and dried over Na2SO4. The solution was concentrated under reduced pressure. The residue was purified by chromatography (0-30% EtOAc/hexanes) to afford N-(7-bromo-3-chloro-1-fluoro-5-(2-hydroxyethyl)-5H-chromeno[2,3-c]pyridin-5-yl)-2-methylpropane-2-sulfinamide (5.8 g, 89% yield) as a light yellow solid. Step 4: To a solution of N-(7-bromo-3-chloro-1-fluoro-5-(2-hydroxyethyl)-5H-chromeno[2,3-c]pyridin-5-yl)-2-methylpropane-2-sulfinamide (5.8 g, 12.14 mmol) in dry MeOH (100 mL) at −20° C. was added a mixture of MeOH (80 mL)/acetylchloride (20 ml). The resulting reaction mixture was stirred at −20° C. for 30 min and then quenched with 10% aqueous solution of Na2CO3. DCM was added, the organic phase was separated and dried over Na2SO4. The solution 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 (4.0 g, 10.71 mmol, 88% yield) as a light yellow solid-foam. Step 5: To a solution of 2-(5-amino-7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)ethanol (4.2 g, 11.24 mmol) in MeOH (40 mL) was added potassium acetate (2.207 g, 22.48 mmol) followed by the drop wise addition of cyanogen bromide (3.0 m solution in DCM; 4.50 mL, 13.49 mmol). The resulting reaction mixture was stirred at RT for 17 h. The reaction mixture was concentrated under reduced pressure, followed by the addition of 4.0 M HCl in dioxane (15 mL). The reaction mixture was stirred at RT for 2 h. The reaction mixture was concentrated under reduced pressure, The residue was dissolved in DCM, washed with aqueous, saturated NaHCO3 solution and brine. The solution was dried over Na2SO4 and concentrated under reduced pressure. The residue was purified by chromatography (0-100% EtOAc/hexanes) to afford 7-bromo-3-chloro-1-fluoro-5′,6′-dihydrospiro[chromeno[2,3-c]pyridine-5,4′-[1,3]oxazin]-2′-amine (Intermediate 11, 1.3 g, 3.26 mmol, 29.0% yield) as a 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.
