[CH3:1][P:2](=[O:7])([O:5][CH3:6])[O:3][CH3:4].[Li]CCCC.C[O:14][C:15](=O)[CH2:16][CH2:17][CH2:18][CH2:19][C:20]1[CH:29]=[CH:28][C:27]2[CH2:26][CH2:25][CH2:24][NH:23][C:22]=2[N:21]=1>C1COCC1>[CH3:4][O:3][P:2]([CH2:1][C:15](=[O:14])[CH2:16][CH2:17][CH2:18][CH2:19][C:20]1[CH:29]=[CH:28][C:27]2[CH2:26][CH2:25][CH2:24][NH:23][C:22]=2[N:21]=1)(=[O:7])[O:5][CH3:6]A solution of dimethyl methylphosphonate (13.20 g, 106.5 mmol) in anhydrous THF (165 mL) was cooled to −78° and treated dropwise with 2.5 M n-BuLi (42.3 mL). After stirring at −78° for 45 min, a solution of ester 1-5 (6.6 g, 26.6 mmol) in THF (35 mL) was added dropwise and the resulting solution stirred for 30 min −78°, quenched with sat. NH4Cl (100 mL), then extracted with ethyl acetate (3×150 mL). The combined organic extracts were dried (MgSO4), filtered, and concentrated to afford a yellow oil. Chromatography on silica gel (5% MeOH/CH2Cl2) afforded 15-1 as a yellow oil.
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