[CH:1]1([CH:6]2[CH2:10][O:9][C:8](=O)[CH2:7]2)[CH2:5][CH2:4][CH2:3][CH2:2]1.[BrH:12].[CH3:13][CH2:14][OH:15]>O>[CH2:14]([O:15][C:8](=[O:9])[CH2:7][CH:6]([CH2:10][Br:12])[CH:1]1[CH2:5][CH2:4][CH2:3][CH2:2]1)[CH3:13]Preparation of 3-bromomethyl-3-cyclopentyl-propionic acid ethyl ester—A solution of 4-cyclopentyl-dihydro-furan-2-one (4.4 g, 28.5 mmol) in 100 mL of EtOH is saturated with HBr at 0° C. The mixture is warmed to room temperature overnight. It is diluted with 200 mL of H2O and extracted with Et2O (3,100 mL). The combined extracts are washed with brine (2.50 mL) and dried over MgSO4. Evaporation of Et2O gives 6.4 g (85% yield) of 3-bromomethyl-3-cyclopentyl-propionic acid ethyl ester as a clear oil. NMR (1H, 400 MHz, CDCl3) δ1.1 (2H, m); 1.2 (3H, t); 1.5 (4H, m); 1.8 (3H, m); 1.9 (1H, m); 2.4 (2H, dd); 3.5 (2H, dd); 4.1 (2H,q).
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