[CH3:1][O:2][C:3]([C:5]1[CH2:6][C:7]2[C:8](=[CH:12][CH:13]=1)[N:9]=[N:10][N:11]=2)=[O:4].[H-].[Na+].CI.[CH3:18]COC(C)=O>CN(C=O)C>[CH3:1][O:2][C:3]([C:5]1[CH:6]([CH3:18])[C:7]2[C:8](=[CH:12][CH:13]=1)[N:9]=[N:10][N:11]=2)=[O:4]1 g of Benzotriazole-5-carboxylic acid methyl ester (5.64 mmol) was dissolved in 20 ml DMF at 0° C. To this solution was added 1 eq. of NaH (60%) at 0° C. The mixture was stirred for 30 min at 0° C., 801 mg (1 eq.) of Methyliodide were slowly added, and the resulting reaction mixture was stirred for 2 h at rt. EtOAc was added and the organic layer was washed extensively with brine and water, dried over MgSO4 and filtered to afford 1 g of crude Methyl-benzotriazole-5-carboxylic acid methyl ester as three different regioisomers. The separation was performed on silica gel using EtOAc/CH 3:7 as eluents.
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