[CH:1]([C:4]1([C:10]([OH:12])=[O:11])[CH2:8][CH2:7][C:6](=[O:9])[CH2:5]1)([CH3:3])[CH3:2].C(Cl)(=O)C(Cl)=O.[CH2:19](O)[C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1.C(N(CC)CC)C>C(Cl)Cl.CN(C=O)C.CN(C1C=CN=CC=1)C>[CH:1]([C:4]1([C:10]([O:12][CH2:19][C:20]2[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=2)=[O:11])[CH2:8][CH2:7][C:6](=[O:9])[CH2:5]1)([CH3:3])[CH3:2]
A cooled (0° C.) solution of 1-isopropyl-3-oxocyclopentanecarboxylic acid (5.44 g, 32.0 mmol) in DCM (75 mL) was treated with oxalyl chloride (8.36 mL, 95.9 mmol), followed by 3 drops of DMF. The reaction mixture was permitted to warm to rt and stir for 1.75 h. The reaction mixture was then concentrated and stored under vacuum for 30 min. The resulting acid chloride was dissolved in DCM (75 mL), cooled to 0° C., and treated with benzyl alcohol (8.28 mL, 80.0 mmol), followed by triethyl amine (8.92 mL, 64.0 mmol, dropwise). Then approximately 100 mg of DMAP was added and the reaction mixture was warmed to rt and stirred for 2 h. The reaction mixture was diluted with DCM and washed with 1N HCl solution, saturated NaHCO3 solution, and brine. The organic layer was dried over anhydrous MgSO4, filtered, and concentrated. Purification by MPLC (silica, 50% ethyl acetate/hexane) gave benzyl 1-isopropyl-3-oxocyclopentanecarboxylate. 1HNMR (CDCl3, 500 MHz): δ 7.36 (m, 5 H), 5.17 (d, J=2.5 Hz, 2H), 2.85 (d, J=18.5 Hz, 1H), 2.48 (m, 1H), 2.29 (dd, J=10.0, 3.0 Hz, 1H), 1.98-2.23 (m, 3H), 1.93 (m, 1H), 0.95 (m, 6H).
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