To a solution of {1-[4-(7-bromo-4-oxo-2-phenyl-4H-chromen-3-yl)-phenyl]-cyclobutyl}-carbamic acid tert-butyl ester (81 mg, 0.15 mmol) in 1,4-dioxane (3.0 mL) in a microwave vial was added hydroxylamine hydrochloride (21 mg, 0.3 mmol), molybdenum hexacarbonyl (20 mg, 0.075 mmol), Herrmann's catalyst (7 mg, 0.0075 mmol) and tri-tert-butylphosphine tetrafluoroborate (4 mg, 0.015 mmol), followed by DBU (22 μL, 0.15 mmol) and DIPEA (51 μL, 0.30 mmol). The vial was sealed, evacuated and flushed twice with nitrogen. The mixture was heated in a microwave at 150° C. for 30 min. The resulting mixture was partitioned between ethyl acetate (40 mL) and water (20 mL) and the phases were separated. The organic layer was washed with brine (20 mL), dried (Na2SO4), filtered and concentrated in vacuo. The resulting residue was subjected to flash chromatography (SiO2, gradient 50-60% ethyl acetate in cyclohexane) to afford the title compound as a white solid (46 mg, 60%). LCMS (Method B): RT=4.57 min, [M+H]+=511.
