[Cl:1][C:2]1[C:7]([O:8]C)=[CH:6][C:5]([N:10]2[C:14](=[O:15])[N:13]([CH:16]([F:18])[F:17])[C:12]([CH3:19])=[N:11]2)=[C:4]([F:20])[CH:3]=1.B(Br)(Br)Br.O>C(Cl)Cl>[Cl:1][C:2]1[C:7]([OH:8])=[CH:6][C:5]([N:10]2[C:14](=[O:15])[N:13]([CH:16]([F:17])[F:18])[C:12]([CH3:19])=[N:11]2)=[C:4]([F:20])[CH:3]=1
A stirred mixture of 4.6 g (0.015 mole) of 1-(4-chloro-2-fluoro-5-methoxyphenyl)-4-difluoromethyl-4,5-dihydro-3-methyl-1,2,4-triazol-5(1H)-one in 200 mL of methylene chloride was cooled to 10° C. and a solution of 11.2 g (0.045) mole of boron tribromide in 45 mL of methylene chloride was added. Upon complete addition the reaction mixture was stirred for four hours as it warmed to ambient temperature. After this time 100 mL of water was added, and stirring was continued for an additional 18 hours. The organic layer was separated, dried with anhydrous magnesium sulfate, and filtered. The filtrate was concentrated under reduced pressure to yield 4.4 g of 1-(4-chloro-2-fluoro-5-hydroxyphenyl)-4-difluoromethyl-4,5-dihydro-3-methyl-1,2,4-triazol-5(1H)-one; mp 147°-152° C.
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