[CH2:1]([Li])[CH2:2][CH2:3]C.[C:6]([O:10][C:11]([N:13]1[CH2:18][CH2:17][C:16](=[O:19])[CH2:15][CH:14]1[C:20]([OH:22])=[O:21])=[O:12])([CH3:9])([CH3:8])[CH3:7].[CH3:23]COC(C)=O.[NH4+].[Cl-]>C1COCC1.O>[CH3:23][O:21][C:20]([CH:14]1[CH2:15][C:16]([CH2:3][CH:2]=[CH2:1])([OH:19])[CH2:17][CH2:18][N:13]1[C:11]([O:10][C:6]([CH3:9])([CH3:7])[CH3:8])=[O:12])=[O:22]
To a stirred solution n-butyllithium (165 mg, 2.6 mmol) in THF (5 mL) at −78° C. was added 12a (P=Boc, P2=Me, m=1) (570 mg, 2.3 mmol) in THF (5 mL). The reaction mixture was stirred at −78° C. for 2 hr and then at −40° C. for an additional 1 hr. EtOAc (20 mL) was added, followed by NH4Cl (5 mL, 10%) and water (10 mL). Organic layer was separated, dried over sodium sulflate and evaporated to dryness. The residue obtained was purified by silica gel column chromatography using 50% EtOAc in hexanes as eluent to provide 4-hydroxy-4-butylproline methylester 12b (P=Boc, m=1, R9=n-butyl) as a colorless oil (0.52 g, 73%): 1H NMR (300 MHz, CDCl3) δ 4.33 (m, 1), 3.76 (d, J=4.8, 3), 3.62 (m, 2), 3.28 (m, 1), 2.13 (m, 1), 2.02 (m, 1), 1.57 (m, 2), 1.29 (m, 12), 0.88 (m, 3); MS (ESPOS): 324 [M+Na]+.
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