[CH3:1][O:2][C:3]1[CH:12]=[C:11]2[C:6]([CH:7]=[CH:8][CH:9]=[C:10]2[CH:13]=[CH:14][C:15]([OH:17])=O)=[CH:5][CH:4]=1.C(Cl)(=O)C(Cl)=O.[Cl-].[CH3:25][NH:26][O:27][CH3:28].C([O-])([O-])=O.[Na+].[Na+]>C(Cl)Cl.O>[CH3:28][O:27][N:26]([CH3:25])[C:15](=[O:17])[CH:14]=[CH:13][C:10]1[C:11]2[C:6](=[CH:5][CH:4]=[C:3]([O:2][CH3:1])[CH:12]=2)[CH:7]=[CH:8][CH:9]=1The acid chloride obtained starting from 6.5 g (28.5 mmol) of the acid obtained in Step E and 5 ml of oxalyl chloride are added dropwise to a suspension of N,O-dimethylhydroxylamine chloride (5.6 g) in a mixture of CH2Cl2/H2O in the presence of 3 g of Na2CO3. The protected acid is obtained in the form of a pale yellow solid.
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