C(NC(C)C)(C)C.[CH2:8]([Li])[CH2:9][CH2:10][CH3:11].[CH:13]1([C:18]([O:20][CH3:21])=[O:19])[CH2:17][CH2:16][CH2:15][CH2:14]1.BrCCC=C>O1CCCC1.CN(P(N(C)C)(N(C)C)=O)C>[CH3:21][O:20][C:18]([C:13]1([CH2:11][CH2:10][CH:9]=[CH2:8])[CH2:17][CH2:16][CH2:15][CH2:14]1)=[O:19]
To a solution of diisopropylamine (10.5 mL, 75 mmol) in tetrahydrofuran (100 mL) pre-cooled to −75° C. was added a 2.5 M solution of n-butyllithium in hexanes (30 mL, 75 mmol) dropwise. Following addition, the reaction mixture was warmed to 0° C. for 30 min and then re-cooled to −75° C. To the mixture was added a solution of methyl cyclopentane carboxylate (8 g, 62 mmol) in tetrahydrofuran (40 mL) dropwise. After stirring for 30 min, a solution of 4-bromo-1-butene (8.2 mL, 81 mmol) in HMPA (6 mL) was added dropwise. The cooling bath was removed to allow the mixture to warm to 20° C. After 1.5 h, the reaction mixture was poured into ice/H2O (200 mL). The two layers were separated and the aqueous layer was extracted with Et2O (100 mL). The organic solutions were combined and dried over K2CO3, filtered and concentrated to afford the 12.1 g of the title compound as an oil. LC/MS: RT=3.57 min. MS (ESI) m/z=183 (M+H+)
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