Reaction Steps
A 100 mL round-bottom flask equipped with air cooled reflux condenser and nitrogen inlet adapter was charged with rac-(4aR,12bS)-12b-ethyl-9-(2-methylpyridin-4-yl)-1,2,4,4a,5,6,9,12b-octahydrospiro[benzo[4,5]oxepino[3,2-f]indazole-3,2′-[1,3]dioxolane] (91, R1=2-methylpyridin-4-yl, R2=Ethyl) (1.11 g, 2.65 mmol) and pTSA (0.654 g, 3.44 mmol) in acetone (26.5 mL) and the reaction mixture was heated at about reflux in a heating block for about 16 h, after which additional acetone (26.5 mL) was added and heating continued for 1 h. The reaction mixture was allowed to cool and then was quenched by careful addition of sat. aq. NaHCO3 (25 mL). The mixture was concentrated under reduced pressure and the remainder was partitioned against EtOAc (50 mL). After separating the layers, the aqueous phase was extracted with EtOAc (2×25 mL). The combined organic phases were washed with brine (100 mL), dried over Na2SO4, filtered, and concentrated under reduced pressure to give (4aR,12bS)-12b-ethyl-9-(2-methylpyridin-4-yl)-4,4a,5,6,9,12b-hexahydro-1H-benzo[4,5]oxepino[3,2-f]indazol-3(2H)-one (92, R1=2-methylpyridin-4-yl, R2=Ethyl) (1.00 g, 2.66 mmol, 101% yield), which was used without further purification. LC/MS, method 3, Rt=2.13 min, MS m/z 376 (M+H)+. 1H NMR (400 MHz, CDCl3) δ 8.60 (d, J=5.9 Hz, 1H), 8.25 (s, 1H), 7.95-7.75 (m, 2H), 7.72 (s, 1H), 7.61 (s, 1H), 4.45-4.36 (m, 1H), 3.88-3.71 (m, 1H), 2.93-2.54 (m, 6H), 2.51-2.29 (m, 3H), 2.23-2.06 (m, 1H), 1.96-1.83 (m, 1H), 1.72-1.42 (m, 2H), 0.68 (s, 1H), (t, J=7.5 Hz, 3H).
