[CH3:1][O:2][CH2:3][O:4][C:5]1[C:14]([CH2:15][CH:16]=C)=[C:13]([NH:18][C:19](=[O:21])[CH3:20])[CH:12]=[CH:11][C:6]=1[C:7]([O:9][CH3:10])=[O:8].I([O-])(=O)(=O)=[O:23].[Na+].C1CCCCC1>O1CCOCC1.C(O)(C)(C)C.C(Cl)Cl.[Os](=O)(=O)(=O)=O>[CH3:1][O:2][CH2:3][O:4][C:5]1[C:6]([C:7]([O:9][CH3:10])=[O:8])=[CH:11][CH:12]=[C:13]([NH:18][C:19](=[O:21])[CH3:20])[C:14]=1[CH2:15][CH:16]=[O:23]A solution of 5 g (17.1 mmol) of methyl 2-methoxymethyloxy-3-allyl-4-acetylaminobenzoate in 20 ml of 1,4-dioxane is heated to 45° C. and 0.86 ml (6.86 mmol) of a 1M solution of osmium tetroxide in t-butanol is added in a single portion. Stirring is continued 15 minutes at 45° C. 7.32 g (34.2 mmol) of sodium periodate is added portionwise and stirring is continued 1 hour. Cyclohexane (1 ml) is added and stirring continued for 1 hour. The reaction mixture is then diluted with CH2Cl2 and washed with water. The organic layer is dried over MgSO4, filtered and concentrated. Flash chromatography (10% EtOAc/hexanes) affords pure 2-methoxymethyloxy-3-carbomethoxy-6-acetylaminophenylacetaldehyde which is used directly in the next step.
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