DEAD (2.2 M in toluen, 1.55 mL) was added dropwise to a solution of 1,4-dioxepan-6-ol (265 mg), t-butyl (1,3-dioxoisoindolin-2-yl)carbamate (560 mg) obtained in preparation example 14-(1) and triphenylphosphine (840 mg) in THF (10 mL) under ice-cooling over 3 minutes. The reaction mixture was stirred at 0° C. for 6 minutes, and further stirred at room temperature overnight The reaction mixture was concentrated under reduced pressure. After toluene (2.5 mL) was added to the resulting residue, the precipitated solid was removed by filtration. The filtrate was purified by silica gel column chromatography (ethyl acetate/n-heptane, 20%) to give the title compound (713 mg).
