Boron tribromide → (E)-5-amino-7'-bromo-4'-fluoro-6,7-dihydro-2H-spiro[[1,4]oxazepine-3,9'-xanthen]-2'-ol

A solution of (E)-7′-bromo-4′-fluoro-2′-methoxy-6,7-dihydro-2H-spiro[[1,4]oxazepine-3,9′-xanthen]-5-amine (0.990 g, 2.431 mmol) in DCM (24.31 mL) was cooled in an ice-bath for 5 min. Boron tribromide (0.919 mL, 9.72 mmol) was added dropwise to give a resulting brown mixture. The mixture was stirred for 1 h, at which time a saturated aq. sodium bicarbonate solution (25 mL) was added. The mixture was stirred for 5 min. and concentrated on a rotary evaporator to remove the DCM. The mixture was heated with a heat gun for 5 min, and at this point the solid was scraped from the sides of the flask. The flask was sonicated for 1 min, then reheated for 2 min. The flask was again sonicated for 1 min, then cooled to RT. The solid was filtered. The filter cake was washed twice with water, then air-dried under a stream of N2 (g) for 1.5 h to give (E)-5-amino-7′-bromo-4′-fluoro-6,7-dihydro-2H-spiro[[1,4]oxazepine-3,9′-xanthen]-2′-ol as a light-yellow solid. The solid was used without further purification.