C([Li])CCC.[Cl:6][C:7]1[CH:12]=[CH:11][CH:10]=[C:9]([F:13])[C:8]=1[CH3:14].[C:15](=[O:17])=[O:16]>O1CCCC1>[Cl:6][C:7]1[CH:12]=[CH:11][C:10]([C:15]([OH:17])=[O:16])=[C:9]([F:13])[C:8]=1[CH3:14]n-Butyllithium (2.5 M in hexane, 100 ml) was added to a cooled solution of 2-chloro-6-fluorotoluene (36.1 g) in dry tetrahydrofuran while maintaining the temperature below -60° C. The mixture was stirred at -78° C. overnight then poured onto solid carbon dioxide pellets. The mixture was stirred and allowed to warm to room temperature. It was acidified to pH 1 and extracted with ether. The organic layer was extracted into aqueous sodium hydroxide solution (2 M) and water. The combined aqueous extracts were acidified to pH 1 and the solid formed was filtered off and washed with water and n-hexane to give 4-chloro-2-fluoro-3-methylbenzoic acid (40.35 g) as a white solid, NMR (DMSO-d6) 2.3(d,3H), 7.4(d,1H) 7.7(t,1H).
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