[Br:1][C:2]1[CH:17]=[CH:16][C:5]([C:6]([C@@H:8]2[CH2:12][CH2:11][CH2:10][C@H:9]2[C:13]([OH:15])=[O:14])=[O:7])=[CH:4][CH:3]=1.[CH3:18]OC(OC)(C)C.Cl>CO>[Br:1][C:2]1[CH:3]=[CH:4][C:5]([C:6]([C@@H:8]2[CH2:12][CH2:11][CH2:10][C@H:9]2[C:13]([O:15][CH3:18])=[O:14])=[O:7])=[CH:16][CH:17]=1To a solution of trans-2-(4-bromobenzoyl)cyclopentanecarboxylic acid (2.0 g, 6.26 mmol) in MeOH (70 mL) was added 2,2-dimethoxypropane (1.63 g, 15.65 mmol) and HCl (4.0 M in dioxane) (1.0 mL). The resulting solution was stirred at 40° C. overnight and then evaporated to dryness. The resulting residue was purified by flash chromatography (Biotage Flash 40M) using 7 to 11% ethyl acetate in hexanes to afford methyl trans-2-(4-bromobenzoyl)cyclopentanecarboxylate (1.62 g, 83%). 1H NMR (400 MHz, CD2Cl2) δ 1.70–1.95 (m, 4H), 2.08–2.21 (m, 2H), 3.40 (m, 1H), 3.64 (s, 3H), 4.04 (m, 1H), 7.64 (m, 2H), 7.86 (m, 2H).
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