[CH3:1][P:2](=[O:7])([O:5][CH3:6])[O:3][CH3:4].C([Li])CCC.[C:13]([O:17][C:18]([NH:20][C@@H:21]([CH2:26][CH:27]=[CH2:28])[C:22](OC)=[O:23])=[O:19])([CH3:16])([CH3:15])[CH3:14]>C1COCC1>[CH3:4][O:3][P:2]([CH2:1][C:22](=[O:23])[C@@H:21]([NH:20][C:18](=[O:19])[O:17][C:13]([CH3:15])([CH3:14])[CH3:16])[CH2:26][CH:27]=[CH2:28])([O:5][CH3:6])=[O:7]To a solution of dimethyl methylphosphonate (15.85 mL, 148 mmol) in THF (99 mL) at −78° C. was added n-butyllithium (93 mL, 148 mmol) slowly. After addition was completed, the reaction mixture was stirred for 30 min and then a solution of (S)-methyl 2-(tert-butoxycarbonylamino)pent-4-enoate (6.8 g, 29.7 mmol) in THF (15 mL) was added slowly. Stirring was continued for another 40 min at −78° C. The reaction was then quenched by adding water and diluted with EtOAc. The organic layer was washed with 1 M HCl, saturated NaHCO3 and brine. The organic layer was then dried over MgSO4, filtered and concentrated to give a clear oil. The crude product was then purified by silica gel chromatography to give the desired product (9.3 g, 98%) as colorless oil. MS (ESI) m/z: 599.0 (M+Na)+.
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