A suspension of 7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-one (20 g, 60.9 mmol), (R)-2-methyl-2-propanesulfinamide (14.76 g, 122 mmol), and titanium (IV) ethoxide (25.2 mL, 122 mmol) in THF (250 mL) was heated to 70° C. for 24 h. Additional (R)-2-methyl-2-propanesulfinamide (1.0 equiv) and titanium (IV) ethoxide (1.0 equiv) were added and the reaction mixture was heated for additional 24 h. Additional (R)-2-methyl-2-propanesulfinamide (1.0 equiv) and titanium (IV) ethoxide (1.0 equiv) were added and the reaction mixture was heated for additional 8 h. The reaction mixture was quenched with brine (150 mL). The resulting suspension was filtered through celite, and the filter cake was washed with EtOAc. The filtrate was washed with brine, dried over Na2SO4 and concentrated under reduced pressure. The residue was purified by chromatography (100% hexanes) to afford racemic N-(7-bromo-3-chloro-1-fluoro-5H-chromeno[2,3-c]pyridin-5-ylidene)-2-methylpropane-2-sulfinamide as an orange solid (15 g, 34.7 mmol, 57.1% yield).
