A 200 mL round-bottom flask equipped with air cooled reflux condenser outfitted with a nitrogen inlet adapter was charged with 1-(2-methylpyridin-4-yl)-5,7,8,9-tetrahydro-1H-spiro[cyclohepta[f]indazole-6,2′-[1,3]dioxolane] (82, R1=2-methylpyridin-4-yl) (3.26 g, 9.72 mmol) and PTSA (2.31 g, 12.2 mmol) in acetone (49 mL). The mixture was heated to reflux. After 24 h, the reaction was diluted with additional acetone (50 mL) and water (2.5 mL) was added. After 1 h the reaction was cooled before adding sat. aq. NaHCO3 (30 mL). The mixture was then concentrated under reduced pressure. EtOAc (70 mL) was added, and after separating the layers, the aqueous phase was extracted with EtOAc (2×25 mL). The combined organic phases were washed with brine (75 mL), dried over Na2SO4, filtered, and concentrated under reduced pressure to give 1-(2-methylpyridin-4-yl)-5,7,8,9-tetrahydrocyclohepta[f]indazol-6(1H)-one (6, R1=2-methylpyridin-4-yl) (2.8 g, 99%); LC/MS, method 3, Rt=1.71 min, MS m/z 292 (M+H)+. 1H NMR (400 MHz, CDCl3) δ 8.65-8.60 (m, 1H), 8.20-8.16 (m, 1H), 7.71 (s, 1H), 7.69-7.65 (m, 1H), 7.63-7.59 (m, 2H), 3.85 (s, 2H), 3.21-3.11 (m, 2H), 2.71 (s, 3H), 2.62-2.54 (m, 2H), 2.14-1.94 (m, 2H).
