[F:1][C:2]1([C:9]([OH:11])=[O:10])[CH2:6][CH2:5][CH2:4][CH:3]1[O:7][CH3:8].[C:12](O)([CH3:15])([CH3:14])[CH3:13].C1(N=C=NC2CCCCC2)CCCCC1>CCOCC.CNC1(NC)C=CN=CC1>[C:12]([O:10][C:9]([C:2]1([F:1])[CH2:6][CH2:5][CH2:4][CH:3]1[O:7][CH3:8])=[O:11])([CH3:15])([CH3:14])[CH3:13]The 1-fluoro-2-hydroxy 1-cyclopentanecarboxylic acid methyl ester in cis form (compound number 2a) synthesized in Example 1 was methylated in the same manner as in Example 10 and further hydrolyzed in the same manner as in Example 11 to obtain 1-fluoro-2-methoxy-1-cyclopentanecarboxylic acid in cis form (compound number 12a). 0.4 g (2.7 mmol) of this carboxylic acid, 0.20 g (2.7 mmol) of tertiary butyl alcohol, 0.56 g (3.7 mmol) of dicyclohexylcarbodiimide and 15 mg of 4,4-dimethylaminopyridine were mixed in 5 ml of ether and stirred at room temperature for 2 hours. The reaction solution was filtered, ether was added to the filtrate, and the mixture was successively washed with a diluted hydrochloric acid solution, saturated saline, a saturated aqueous sodium bicarbonate solution and saturated saline. The ether layer was dried over anhydrous magnesium sulfate, and the solvent was distilled away to obtain 0.31 g (yield: 56%) of the objective 2-methoxy-1-fluoro-1-cyclopentanecarboxylic acid tertiary butyl ester in cis form (compound number 20a).
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