[PH2](O)=O.[CH2:4]([O:11][C:12]1[CH:20]=[C:19]2[C:15]([C:16](N)=[N:17][N:18]2[CH2:21][C@H:22]([OH:24])[CH3:23])=[CH:14][CH:13]=1)[C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][CH:6]=1.N(OCC(C)C)=O>CO.O>[CH2:4]([O:11][C:12]1[CH:20]=[C:19]2[C:15]([CH:16]=[N:17][N:18]2[CH2:21][C@H:22]([OH:24])[CH3:23])=[CH:14][CH:13]=1)[C:5]1[CH:6]=[CH:7][CH:8]=[CH:9][CH:10]=1Hypophosphorous acid (3.45 L of a 50% (w/w) aqueous solution) was added to a stirred solution of 2 (1975 g, 6.65 mol) in 23.7 L of methanol under a nitrogen atmosphere. Isobutyl nitrite (1576 mL, 13.3 mol) was added in two portions, keeping the reaction temperature below 53° C. After 3 hours, a solution of Na2HPO4 (8.5 kg) in 70 L of water was added, and the mixture was extracted with ethyl acetate (30 L then 15 L). The combined organic extracts were washed with brine, dried (Na2SO4), treated with decolorizing charcoal, filtered and concentrated in vacuo. The product was purified by trituration with ethyl acetate-hexane followed by elution through silica using an acetone-hexane gradient, to give after concentration in vacuo, 1260 g (67%) of 3.
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