[CH3:1][C:2]1[CH:7]=[C:6]([CH2:8]O)[CH:5]=[C:4]([CH3:10])[C:3]=1[O:11][C:12](=[O:23])[CH2:13][NH:14][CH2:15][C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17].C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1.C(Br)(Br)(Br)[Br:44]>ClCCl>[Br:44][CH2:8][C:6]1[CH:7]=[C:2]([CH3:1])[C:3]([O:11][C:12](=[O:23])[CH2:13][NH:14][CH2:15][C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])=[C:4]([CH3:10])[CH:5]=1A 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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