[O:1]1[CH2:6][CH2:5][CH2:4][CH2:3][CH:2]1[N:7]1[CH:11]=[CH:10][CH:9]=[N:8]1.C([Li])CCC.B(F)(F)F.CCOCC.[CH:26]12[O:31][CH:27]1[CH2:28][CH2:29][CH2:30]2.C(=O)([O-])O.[Na+]>C1COCC1>[O:1]1[CH2:6][CH2:5][CH2:4][CH2:3][CH:2]1[N:7]1[C:11]([C@H:26]2[CH2:30][CH2:29][CH2:28][C@@H:27]2[OH:31])=[CH:10][CH:9]=[N:8]1To a solution of 1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole (3.04 g, 20.0 mmol) in THF (30 mL), n-butyl lithium (1.63 M solution in hexane; 12.7 mL, 20.7 mmol) was added dropwise at −78° C. for 7 minutes. The reaction solution was stirred for 30 minutes, and boron trifluoride-ethyl ether (3.14 mL, 25.0 mmol) was then added thereto. The reaction solution was further stirred for 10 minutes. Then, cyclopentene oxide (2.08 mL, 24.0 mmol) was added thereto, and the reaction solution was stirred at −78° C. for 3 hours. To the reaction solution, a saturated aqueous solution of sodium hydrogencarbonate (15 mL) was added, followed by extraction four times with ethyl acetate (20 mL). The thus obtained organic layer was dried over anhydrous sodium sulfate. After vacuum concentration, the residue was purified with silica gel chromatography (hexane/ethyl acetate=1:4) to yield the title compound (1.54 g, 33%) in the form of a diastereomeric mixture as a colorless oil.
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