C([Li])CCC.[F:6][C:7]1[CH:16]=[CH:15][C:10]2[CH2:11][CH2:12][CH2:13][O:14][C:9]=2[CH:8]=1.[C:17](=[O:19])=[O:18].C(OCC)C>O1CCCC1>[F:6][C:7]1[CH:16]=[CH:15][C:10]2[CH2:11][CH2:12][CH2:13][O:14][C:9]=2[C:8]=1[C:17]([OH:19])=[O:18]A stirred solution of 30.4 mL (0.076 mole) of n-butyllithium (2.5M in hexanes) in 200 mL of tetrahydrofuran was cooled to -78 °C., and 10.5 grams (0.069 mole) of 3,4-dihydro-7-fluoro-2H-1-benzopyran was added portionwise. Upon completion of the addition, the reaction mixture was maintained at -78° C. for 30 minutes. The reaction mixture was then exposed to a carbon dioxide atmosphere for 18 hours. The reaction mixture was then stirred with diethyl ether and extracted with an aqueous 5% sodium hydroxide solution. The basic layer was washed with diethyl ether, made acidic with concentrated hydrochloric acid, and then extracted with diethyl ether. The extract was dried with magnesium sulfate and filtered. The filtrate was concentrated under reduced pressure, yielding 10.2 grams of 3,4-dihydro-7-fluoro-2H-1-benzopyran-8-ylcarboxylic acid. The NMR spectrum was consistent with the proposed structure.
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