Reaction Steps
In a 250-mL flask, Lawesson's reagent (0.577 g, 1.427 mmol) and (S)-2′-bromo-4′-fluoro-7′-methoxyspiro[morpholine-3,9′-xanthen]-5-one (0.978 g, 2.481 mmol) were suspended in toluene (25 mL). An air-cooled condenser was attached, and the flask was heated in a 90° C. oil bath for 3 h. The mixture was then cooled and concentrated to give (S)-2′-bromo-4′-fluoro-7′-methoxyspiro[morpholine-3,9′-xanthene]-5-thione which was used in the next step without further purification. Step 2: In a 150-mL resealable vessel, the crude (S)-2′-bromo-4′-fluoro-7′-methoxyspiro[morpholine-3,9′-xanthene]-5-thione (1.0 g, 2.437 mmol) was dissolved in a dioxane solution of ammonia (0.5 M, 58.5 mL, 29.2 mmol). Mercury (II) chloride (0.993 g, 3.66 mmol) was added, and the vessel was sealed and heated in a 55° C. oil bath overnight. The mixture was then cooled and concentrated. The residue was filtered through Celite, rinsing with 10% MeOH-DCM (400 mL). The filtrate was concentrated, and the residue was purified through silica gel (150 mL) using 7.5% MeOH-DCM to afford 131 mg of (S)-2′-bromo-4′-fluoro-7′-methoxy-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine Step 3: In a 500-mL flask, the (S)-2′-bromo-4′-fluoro-7′-methoxy-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (0.595 g, 1.513 mmol) was dissolved in DCM (45 mL). The orange solution was cooled to 0° C. and a DCM solution of boron tribromide (1.0 M, 4.54 mL, 4.54 mmol) was added. After 2 h, the reaction mixture was quenched with 20 mL of 9:1 NH4Cl/NH4OH. The mixture was diluted further with water (10 mL) and the aqueous phase was extracted with 5% MeOH-dcm (3×60 mL). The organics were combined, washed with brine (20 mL), dried over sodium sulfate and concentrated to afford crude (S)-5-amino-2′-bromo-4′-fluoro-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-7′-ol (0.574 g, 1.21 mmol) which was used directly in the next step. Step 4: In a microwave vial, the potassium phosphate (0.771 g, 3.63 mmol), PdCl2(AmPhos)2 (0.064 g, 0.091 mmol) and 2-(5,6-dihydro-2H-pyran-3-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.356 g, 1.695 mmol) were loaded. The (S)-5-amino-2′-bromo-4′-fluoro-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-7′-ol (0.459 g, 1.211 mmol) was added as a solution in dioxane (6 mL). Water (2.4 mL) was added and argon gas was blown through the vessel, which was sealed and heated by microwave at 120° C. for 30 min. The residue was taken up in half-saturated aqueous NH4Cl (30 mL) and the aqueous phase was extracted with 5% MeOH/DCM (3×25 mL). The organics were combined, washed with brine (7 mL), dried over sodium sulfate and concentrated to afford crude (S)-5-amino-2′-(5,6-dihydro-2H-pyran-3-yl)-4′-fluoro-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-7′-ol which was used directly in the next step. Step 5: Crude (S)-5-amino-2′-(5,6-dihydro-2H-pyran-3-l)-4′-fluoro-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-7′-ol (0.463 g, 1.211 mmol) was dissolved in DCM (35 mL). The solution was cooled to 0° C., and TEA (0.175 mL, 1.27 mmol) was added, followed by N-(5-chloropyridin-2-yl)-1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methanesulfonamide (0.427 g, 1.09 mmol). The solution was allowed to warm naturally. After 9 h, the reaction was quenched with 1 M aqueous NaOH (15 mL). The aqueous layer was separated and extracted further with 5% MeOH-DCM (3×20 mL). The organics were combined, washed with brine (7 mL), dried over sodium sulfate and concentrated. The residue was partially purified by chromatography (5% MeOH/DCM) to afford (S)-5-amino-2′-(5,6-dihydro-2H-pyran-3-yl)-4′-fluoro-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthene]-7′-yl trifluoromethanesulfonate (393 mg, 0.764 mmol). Step 6: In a microwave vial, the pyridin-3-ylboronic acid (0.061 g, 0.495 mmol), (S)-5-amino-2′-(5,6-dihydro-2H-pyran-3-yl)-4′-fluoro-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthene]-7′-yl trifluoromethanesulfonate (0.196 g, 0.381 mmol), and Pd(PPh3)4 (0.044 g, 0.038 mmol) were suspended in dmf (4.1 mL). Aqueous sodium carbonate (1.0 M, 1.143 mL, 1.143 mmol) was added. Argon was blown through the vessel, which was sealed and heated in an 85° C. oil bath (11:40). After 1.5 h the reaction was concentrated. The residue was taken up in EtOAc (100 mL) and the organic layer was extracted with water (15 mL), brine (, then was dried over sodium sulfate and concentrated. The residue was purified by chromatography (7.5% MeOH/DCM) to afford (S)-2′-(5,6-dihydro-2H-pyran-3-yl)-4′-fluoro-7′-(pyridin-3-yl)-2,6-dihydrospiro[[1,4]oxazine-3,9′-xanthen]-5-amine (99 mg, 0.22 mmol). MS (m/z) 444 (M+H)+. 1H NMR (400 MHz, CDCl3) δ ppm; 8.85 (s, 1 H), 8.57 (d, 1 H, J=4.5 Hz), 7.86 (d, 1 H, J=8.0 Hz), 7.50 (m, 2 H), 7.36 (m, 2 H), 7.08 (dd, 1 H, J=11.7, 2.0 Hz), 6.99 (s, 1 H), 6.17 (s, 1 H), 4.46 (m, 2 H), 4.33 (s, 2 H), 3.85 (t, 2 H, J=5.7 Hz), 3.57 (m, 2 H), 2.33 (m, 2 H).
