[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][CH2:10][CH:9]1[CH:13]=[CH:14][C:15](OCC)=[O:16])=[O:7])([CH3:4])([CH3:3])[CH3:2].C(Cl)Cl.B(F)(F)F.CCOCC.CC(C[AlH]CC(C)C)C>CCOC(C)=O>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][CH2:10][CH:9]1[CH:13]=[CH:14][CH2:15][OH:16])=[O:7])([CH3:4])([CH3:3])[CH3:2]A 2 L, 3-necked round bottomed flask equipped with an overhead stirred was charged with 14 (67 g, 0.20 mol) and DCM (400 mL). The solution was cooled to −78° C. To this solution was slowly added boron trifluoride etherate (30 mL, 0.20 mol). The reaction mixture was stirred for 30 min. DIBAL (1 M in DCM, 600 mL, 0.6 mol) was added at a moderate rate. The solution was stirred at −78° C. for 2 h and then treated with EtOAc (100 mL) over 30 min to discharge remaining reagent. The reaction mixture was allowed to warm to −5° C. The reaction mixture was CAREFULLY quenched by the dropwise addition of 1 M HCl. The reaction mixture was diluted with DCM and H2O and made acidic to dissolve aluminum salts. The layers were separated and the organic phase was washed successively with dilute aqueous HCl, water, and brine. The DCM layer was dried over Na2SO4, filtered, and concentrated. The residue was purified by flash chromatography (SiO2, 25% to 80% EtOAc/hexane) to afford 15 as a yellow oil (36 g, 79%). [TLC analysis, 1:1 hexane/EtOAc, Rf(14)=0.8; Rf(15)=0.2]. 1H NMR (CDCl3, 300 MHz) δ5.73-5.52 (m, 2H), 4.39-4.16 (m, 1H), 4.15-4.04 (m, 2H), 3.46-3.25 (m, 2H), 2.92 (br s, 1H), 2.08-1.93 (m, 1H), 1.92-1.79 (m, 2H), 1.78-1.62 (m, 1H), 1.42 (s, 9H) ppm.
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