[C:1]([O:5][C:6]([CH2:8][NH:9][CH2:10][C:11]([O:13][C:14]1[C:21]([CH3:22])=[CH:20][C:17]([CH:18]=[O:19])=[CH:16][C:15]=1[CH3:23])=[O:12])=[O:7])([CH3:4])([CH3:3])[CH3:2].[BH4-].[Na+]>O1CCCC1.C(OCC)(=O)C>[CH3:22][C:21]1[CH:20]=[C:17]([CH2:18][OH:19])[CH:16]=[C:15]([CH3:23])[C:14]=1[O:13][C:11](=[O:12])[CH2:10][NH:9][CH2:8][C:6]([O:5][C:1]([CH3:3])([CH3:2])[CH3:4])=[O:7]A mixture of 2.88 g of 4-(tert-butoxycarbonylmethylamino)acetoxy-3,5-dimethylbenzaldehyde and 0.34 g of sodium borohydride in 25 ml of tetrahydrofuran was stirred for 2 h at room temperature. The mixture was diluted with ethyl acetate and was washed with 0.25N HCl. The organic layer was dried over anhydrous sodium sulfate and concentrated to obtain (tert-butoxycarbonylmethylamino)acetic acid 2,6-dimethyl-4-hydroxymethylphenyl ester (2.9 g) as a colourless syrup. To a solution of 2.8 g of (tert-butoxycarbonylmethylamino)acetic acid 2,6-dimethyl-4-hydroxymethylphenyl ester and 2.73 g of triphenylphosphine in 30 ml of dichloromethane, 3.44 g of carbon tetrabromide was added and the mixture was stirred for 1 h at room temperature. The mixture was concentrated and the residue was chromatographed on silica gel (Wakogel C-200, solvent: CH2Cl2)to obtain (tert-butoxycarbonylmethylamino)acetic acid 4-bromomethyl-2,6-dimethylphenyl ester (2.97 g, 89% ) as a colourless oil.
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