6′-((3,3-Difluorocyclobutyl)methoxy)spiro[cyclohexane-1,2′-indene]-1′,4(3′H)-dione (Intermediate 12, 3.51 g, 10.5 mmol) were dissolved in the mixture of THF (50 mL) and methanol (4.25 mL, 105 mmol). Borane-trimethylamine complex (1.69 g, 23.1 mmol) was added and the mixture was stirred overnight. Citric acid monohydrate (30.9 g, 147 mmol) was added in one portion, followed by dropwise addition of water (3.78 mL, 210 mmol). The mixture was stirred for 3 h before being diluted with water and extracted with EtOAc (×2). The combined organic phases were dried and concentrated. The product was purified using column chromatography (0-10% MeOH in DCM), providing 2.98 g (quantitative yield) of the title compound. MS (ES+) m/z 337 [M+H]+.
