[CH2:1]([O:3][C:4](=[O:14])[CH2:5][CH:6]([CH2:12]Br)[CH:7]1[CH2:11][CH2:10][CH2:9][CH2:8]1)[CH3:2].[N-:15]=[N+:16]=[N-:17].[Na+]>CS(C)=O.O>[CH2:1]([O:3][C:4](=[O:14])[CH2:5][CH:6]([CH2:12][N:15]=[N+:16]=[N-:17])[CH:7]1[CH2:11][CH2:10][CH2:9][CH2:8]1)[CH3:2]Preparation of 3-Azidomethyl-3-cyclopentyl-propionic acid ethyl ester—A solution of 3-bromomethyl-3-cyclopentyl-propionic acid ethyl ester (4.4 g, 28.5 mmol) and NaN3 (2.0 g, 31.4 mmol) in 25 mL of DMSO is warmed to 60° C. for 12 hours. The mixture is cooled to room temperature and diluted with 100 mL of H2O. Extraction with Et2O (3×50 mL) and drying over MgSO4 followed by evaporation of the Et2O gives 4.8 g (75% yield) of 3-azidomethyl-3-cyclopentyl-propionic acid ethyl ester as an oil. NMR (1H, 300 MHz, CDCl3) δ1.1 (2H, m); 1.2 (3H, t); 1.6 (4H, m); 1.8 (3H, m); 1.9 (1H, m); 2.4 (2H, dd); 3.4 (2H, dd); 4.1 (2H, q).
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