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 2-(5-amino-7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-yl)ethanol (0.50 g, 1.338 mmol) in THF (10 mL) was added 4-nitrobenzoyl isothiocyanate (0.306 g, 1.472 mmol) and the reaction mixture was stirred at RT for 25 min. TEA (0.019 mL, 0.134 mmol) and 1,3-dicyclohexylcarbodiimide (0.304 g, 1.472 mmol) were added and the reaction mixture was heated at 70° C. for 1.5 h. The reaction mixture was allowed to warm to RT and concentrated under reduced pressure. The residue was dissolved in MeOH (15 mL) and potassium carbonate (0.555 g, 4.01 mmol) was added. The resulting mixture was stirred at rt overnight. The reaction mixture was concentrated under reduced pressure, washed with water and extracted with DCM. The combined organic layers were dried over Na2SO4 and the solvent was removed under reduced pressure. The residue was purified by chromatography (0-40% EtOAc/hexanes) to afford 7-bromo-3-chloro-1-methoxy-5′,6′-dihydrospiro[chromeno[2,3-c]pyridine-5,4′-[1,3]oxazin]-2′-amine (0.45 g, 1.096 mmol, 82% yield) as a yellow solid.
