Br[CH2:2][C:3]1[O:4][CH:5]=[C:6]([OH:10])[C:7](=[O:9])[CH:8]=1.[C:11]([O:15][C:16]([N:18]1[CH2:23][CH2:22][NH:21][CH2:20][CH2:19]1)=[O:17])([CH3:14])([CH3:13])[CH3:12].C(N(CC)CC)C>C(#N)C>[OH:10][C:6]1[C:7](=[O:9])[CH:8]=[C:3]([CH2:2][N:21]2[CH2:20][CH2:19][N:18]([C:16]([O:15][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:17])[CH2:23][CH2:22]2)[O:4][CH:5]=12-(Bromomethyl)-5-hydroxy-4H-pyran-4-one (8.9 g, 43.4 mmol), tert-butyloxycarbonylpiperazine (8.5 g, 45.6 mmol), triethylamine (7 mL, 49.9 mmol) and acetonitrile (200 mL) were charged in a 500 ml round-bottomed flask equipped with a magnetic stirrer. The reaction mixture was stirred for 2 h at 90° C. Acetonitrile was evaporated and EtOAc (50 mL) was added. The precipitate of (C2H5)3N, HCl was filtered off and ethyl acetate was evaporated at 40° C. to dryness. The crude compound was purified by column chromatography (deactivated SiO2:CH2Cl2:triethylamine 98:2 to CH2Cl2:MeOH 95:5, purification: CH2Cl2:MeOH 99.5:0:5 to 96:4) to give after evaporation tert-butyl 4-((5-hydroxy-4-oxo-4H-pyran-2-yl)methyl)piperazine-1-carboxylate 24 (10.5 g, 78% yield) as a white powder.
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