C(OP([CH2:9][C:10]([O:12][CH2:13][CH3:14])=[O:11])(OCC)=O)C.[H-].[Na+].O=[C:18]1[CH2:21][N:20]([C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=[O:23])[CH2:19]1>C1COCC1>[CH2:13]([O:12][C:10](=[O:11])[CH:9]=[C:18]1[CH2:19][N:20]([C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=[O:23])[CH2:21]1)[CH3:14]To an ice-cold solution of ethyl 2-diethoxyphosphorylacetate (25.9 g, 116 mmol) in THF (200 mL) was added carefully NaH (60% dispersion in mineral oil, 4.62 g, 116 mmol) over 25 min. The cold bath was removed and after 30 min, tert-butyl 3-oxoazetidine-1-carboxylate (9.88 g, 57.7 mmol) in THF (40 mL) was added over 5 min. After 30 min, the reaction mixture was quenched with water and extracted twice with ethyl acetate. The combined organics were washed with brine, dried (MgSO4), filtered and concentrated. Purification by column chromatography (6/1 Pet ether/ethyl acetate) gave the ester (8.59 g, 62%) as a colourless oil.
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