ClC(O[CH2:5][CH:6](C)C)=O.[C:9]([O:13][C:14]([NH:16][CH2:17][P:18]([CH2:21][NH:22][C:23]([O:25][C:26]([CH3:29])([CH3:28])[CH3:27])=[O:24])(=[O:20])[OH:19])=[O:15])([CH3:12])([CH3:11])[CH3:10].C(O)C.C(N(CC)CC)C>C(Cl)Cl>[C:9]([O:13][C:14]([NH:16][CH2:17][P:18]([CH2:21][NH:22][C:23]([O:25][C:26]([CH3:29])([CH3:28])[CH3:27])=[O:24])(=[O:19])[O:20][CH2:5][CH3:6])=[O:15])([CH3:12])([CH3:11])[CH3:10]Isobutyl chloroformate (1.50 ml; 11.48 mmol) is added dropwise and with stirring to a solution of the phosphinic acid 1 (3.200 g; 9.88 mmol) in a mixture of methylene chloride (50 ml), ethanol (3.00 ml; 51.59 mmol), triethylamine (1.40 ml; 10.06 mmol) and N,N-dimethylaminopyridine (10 mg) at 0° C. After 90 minutes the reaction solution is extracted with saturated aqueous ammonium chloride solution (30 ml) and saturated aqueous KHCO3 solution (30 ml). The organic phase is dried over Na2SO4 and evaporated under reduced pressure. The phosphinate 2 (700 mg, 20% of theory) is obtained after purification on silica gel, using column chromatography (ethyl acetate/heptane=3/2). Spectroscopic data is given above.
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