A 250-mL round-bottom flask was charged with 3-((9-amino-7-bromo-4-fluoro-2-methoxy-9H-xanthen-9-yl)methoxy)propanenitrile (2.78 g, 6.83 mmol) and toluene (45.5 mL) to give a pale-green solution. Trimethylaluminum (7.17 mL of a 2M solution in toluene, 14.34 mmol) was added, and a reflux condenser was attached. After stirring for 1 min, the flask was heated to 90° C. for 1 h. After this time, the mixture was cooled to RT. Sodium sulfate decahydrate (3.4 g) was added slowly over 5 min, and the mixture was stirred overnight. In the morning, the mixture was diluted with EtOAc (50 mL) and filtered through celite. The filter pad was washed with EtOAc (3×50 mL). The combined filtrates were concentrated to give a pale-yellow solid. The crude product was purified by chromatography on silica gel (0-10% MeOH/DCM) to give (E)-7′-bromo-4′-fluoro-2′-methoxy-6,7-dihydro-2H-spiro[[1,4]oxazepine-3,9′-xanthen]-5-amine as a white solid. 1H NMR (400 MHz, DMSO-d6) δ=7.53 (d, J=2.4 Hz, 1 H), 7.47 (dd, J=2.5, 8.6 Hz, 1 H), 7.18 (d, J=8.6 Hz, 1 H), 6.95 (dd, J=2.9, 12.3 Hz, 1 H), 6.69 (dd, J=1.5, 2.9 Hz, 1 H), 6.15 (br. s., 2 H), 3.83-3.69 (m, 5 H), 3.64-3.45 (m, 2 H), 3.00-2.74 (m, 2 H). MS m/z=411.0. Calc'd for C18H17BrFN2O3: 407.1.
