[F:1][C:2]1[CH:7]=[CH:6][C:5]([OH:8])=[CH:4][CH:3]=1.C(=O)([O-])[O-].[Cs+].[Cs+].[C:15]([O:19][C:20]([NH:22][CH2:23][CH2:24]OS(C)(=O)=O)=[O:21])([CH3:18])([CH3:17])[CH3:16].O>CN(C=O)C>[C:15]([O:19][C:20](=[O:21])[NH:22][CH2:23][CH2:24][O:8][C:5]1[CH:6]=[CH:7][C:2]([F:1])=[CH:3][CH:4]=1)([CH3:18])([CH3:17])[CH3:16]Next, to a solution of 4-fluorophenol (0.47 g, 4.18 mmol) in DMF (10 mL) was added cesium carbonate (2.72 g, 8.36 mmol) at room temperature. The mixture was stirred at ambient temperature for 15 minutes, then methanesulfonic acid 2-(tert-butoxycarbonylamino)ethyl ester (1.00 g, 4.18 mmol) was added. The reaction mixture was stirred at 100° C. for 16 hours. Water was added and the mixture was concentrated in vacuo. Product mixture was dissolved in ethyl acetate and was washed with water, then with brine. The organic layer was dried over Na2SO4, and the solvent was removed under reduced pressure. The residue was purified by column chromatography (ethyl acetate:hexane=7:1 to 4:1), and obtained [2-(4-fluorophenoxy)ethyl]carbamic acid tert-butyl ester as yellow oil (0.61 g, 57.4% yield).
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