[C:1]([C:4]12[CH2:11][CH:10]3[CH2:12][C:6]([C:13]([O:15][CH3:16])=[O:14])([CH2:7][CH:8]1[CH2:9]3)[CH2:5]2)(=[O:3])[CH3:2].[CH2:17](O)[CH2:18][OH:19].CC1C=CC(S(O)(=O)=O)=CC=1.C([O-])(O)=O.[Na+]>C1C=CC=CC=1>[CH3:2][C:1]1([C:4]23[CH2:11][CH:10]4[CH2:12][C:6]([C:13]([O:15][CH3:16])=[O:14])([CH2:7][CH:8]2[CH2:9]4)[CH2:5]3)[O:19][CH2:18][CH2:17][O:3]1A mixture of methyl 3-acetyltricyclo[3.3.1.03,7]nonane-1-carboxylate (2.0 g, 8.9 mmol) obtained in step II, 1,2-ethanediol (8.9 mL), p-TSA (47 mg, 5 mol %) and benzene (36 mL) was refluxed using a Dean-Stark apparatus for 1 h. The reaction mixture was cooled to room temperature, 10% aq. NaHCO3 (36 mL) was added, and the two layers were separated. The aqueous layer was extracted with EtOAc. The combined organic layers were washed with brine, dried over Na2SO4, and the solvent was evaporated under reduced pressure to obtain methyl 3-(2-methyl-1,3-dioxolan-2-yl)tricyclo[3.3.1.03,7]nonane-1-carboxylate (2.2 g) in 93% yield as viscous liquid. m/z (M+1) 267. IR cm−1 2954, 1731, 1698, 1460, 1236, 1046, 752. 1H NMR (CDCl3) 300 MHz δ 4.07-3.94 (m, 4H), 3.66 (s 3-H), 2.44-2.36 (m 2-H), 2.27-2.18 (m, 1H), 2.12-2.02 (m, 1H), 1.94-1.81 (m, 8-H), 1.30 (s, 3H).
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