Sodium sulfate decahydrate → (5-amino-3-bromo-7-iodo-5H-chromeno[2,3-b]pyridin-5-yl)methanol

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To a suspension of 3-bromo-7-iodo-5H-chromeno[2,3-b]pyridin-5-one (20.00 g, 49.8 mmol) and trimethylsulfonium iodide (11.17 g, 54.7 mmol) in 250 mL DMSO under nitrogen atmosphere was added lithium tert-butoxide [1N in heptane (54.7 mL, 54.7 mmol)] drop wise over 40 minutes. After stirring for an additional 30 minutes, trimethylsilylazide (13.21 mL, 100 mmol) was added. After stirring for an additional hour, the reaction mixture was concentrated under reduced pressure. The remaining solution was diluted with water. The resulting solid was filtered off and washed with water. The solid was dissolved in 2-MeTHF, dried over MgSO4 and concentrated. The crude residue was dissolved in 200 mL THF, cooled to 0° C. and treated with LAH (1.888 g, 49.8 mmol). After stirring for 30 minutes, the cooling bath was removed, and the reaction mixture was allowed to stir for an additional 30 minutes. The reaction mixture was then cooled to 0° C. and quenched with sodium sulfate decahydrate (32.1 g, 100 mmol). The reaction mixture was vigorously stirred for one hour, filtered through a plug of celite and concentrated. Purification of the crude residue by column chromatography [0-80% (95:5 EtOAc/MeOH)/DCM] gave (5-amino-3-bromo-7-iodo-5H-chromeno[2,3-b]pyridin-5-yl)methanol (8.80 g, 20.32 mmol, 40.8% yield). Step 2: A solution of (5-amino-3-bromo-7-iodo-5H-chromeno[2,3-b]pyridin-5-yl)methanol (10.00 g, 23.09 mmol) and bromoacetonitrile (12.06 mL, 173 mmol) in 25 mL THF was heated to 40° C. Lithium tert-butoxide [1N in THF (173 mL, 173 mmol)] was added drop wise via addition funnel over 5 hours. After completed addition, the reaction mixture was concentrated. The residue was purified by column chromatography [0-80% (95:5 EtOAc/MeOH)/heptane] to yield 2-((5-amino-3-bromo-7-iodo-5H-chromeno[2,3-b]pyridin-5-yl)methoxy)acetonitrile (5.58 g, 11.82 mmol, 51.2% yield). Step 3: A solution of 2-((5-amino-3-bromo-7-iodo-5H-chromeno[2,3-b]pyridin-5-yl)methoxy)acetonitrile (5.58 g, 11.82 mmol) in 100 mL 2-MeTHF under nitrogen atmosphere was treated with trimethylaluminum [2N in heptane (7.98 mL, 15.96 mmol)]. After stirring for 10 minutes at RT, the reaction mixture was heated to 80° C. for 90 minutes. The reaction mixture was cooled to RT and quenched with MeOH. The reaction mixture was treated with saturated Rochelle's salt solution and vigorously stirred for an additional hour. The organic layer was separated, washed with brine, dried over MgSO4 and concentrated under reduced pressure. Purification of the crude residue by column chromatography [0-80% (90:10:1 DCM/MeOH/NH4OH)/DCM] gave 3-bromo-7-iodo-2′,6′-dihydrospiro[chromeno[2,3-b]pyridine-5,3′-[1,4]oxazin]-5′-amine (Intermediate 2, 2.97 g). Step 4: Intermediates (R)-3-bromo-7-iodo-2′,6′-dihydrospiro[chromeno[2,3-b]pyridine-5,3′-[1,4]oxazin]-5′-amine (11A) and (S)-3-bromo-7-iodo-2′,6′-dihydrospiro[chromeno[2,3-b]pyridine-5,3′-[1,4]oxazin]-5′-amine (11B) were obtained form racemic 3-bromo-7-iodo-2′,6′-dihydrospiro[chromeno[2,3-b]pyridine-5,3′-[1,4]oxazin]-5′-amine using similar chiral separation conditions as described herein for intermediate 10.

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