Boron tribromide → 5-Amino-4'-fluoro-7'-(2-fluoropyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9'-xanthen]-2'-ol

A 250 ml RB flask was charged with 7′-bromo-4′-fluoro-2′-methoxy-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (2.73 g, 6.94 mmol), bis(di-tert-butyl(4-dimethylaminophenyl)phosphine)dichloropalladium(II) (0.492 g, 0.694 mmol) and 2-fluoropyridin-3-ylboronic acid (1.467 g, 10.41 mmol). Dioxane (40 mL) and potassium carbonate (1M solution) (20.83 mL, 20.83 mmol) were added and the mixture was flushed with argon and heated at 85° C. for 30 minutes. The mixture was cooled to RT, diluted with EtOAc and the organic layer was separated and concentrated in vacuo to give a yellow semisolid. After trituration with 10 ml of EtOH the solid was filtered, washed with EtOH (2×1 ml) and dried on air overnight to afford 4′-fluoro-7′-(2-fluoropyridin-3-yl)-2′-methoxy-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (2.11 g, 5.15 mmol). Step 2: To a suspension of 4′-fluoro-7′-(2-fluoropyridin-3-yl)-2′-methoxy-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (1.668 g, 4.07 mmol) in DCM (12 ml) was added boron tribromide (0.963 mL, 10.19 mmol). Stirring was continued for 45 hrs at 0° C. at which point the mixture was removed from the bath and stirred for 2 hrs at RT. The reaction mixture was recooled to 0° C. and quenched by careful addition of saturated aqueous NaHCO3 solution (˜10 mL). The mixture became colorless with a white precipitate. The solvent was removed in vacuo, the mixture was diluted with water and filtered. The solid was washed with water and dried on air for 2 hrs, then for 2 hrs in high vacuum at RT to afford 5-amino-4′-fluoro-7′-(2-fluoropyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-2′-ol (1.53 g, 3.87 mmol, 95% yield). Step 3: To a solution of 5-amino-4′-fluoro-7′-(2-fluoropyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-2′-ol (200 mg, 0.506 mmol) in DMF (2529 μL) cesium carbonate (330 mg, 1.012 mmol), KI (25.2 mg, 0.152 mmol) and 2-fluoro-2-methylpropyl trifluoromethanesulfonate (125 mg, 0.556 mmol) were added sequentially and the resulting mixture was stirred overnight at RT. The mixture was diluted with 5 ml of water and stirred for 5 minutes. The solvents were decanted from a precipitated gummy solid. 10 ml of water was added and the mixture was stirred for 1 hr at RT at which point a fine precipitate formed. The solids were filtered, washed with water and dried on air for 3 hr, then overnight in vacuo to afford racemic 4′-fluoro-2′-(2-fluoro-2-methylpropoxy)-7′-(2-fluoropyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (175 mg, 73% yield). Step 4: The final compound (S)-4′-fluoro-2′-(2-fluoro-2-methylpropoxy)-7′-(2-fluoropyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (37A) was obtained form racemic 4′-fluoro-2′-(2-fluoro-2-methylpropoxy)-7′-(2-fluoropyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine using similar chiral separation conditions as described herein for intermediate 10.