N-bromobutanimide → 1-Bromomethyl-4-chloro-3-(2,4-dichloro-5-(dibromomethyl)phenyl)-5-difluoromethoxy-1H-pyrazole

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A solution of 6 g (12 mmol) of 4-chloro-3-(2,4-dichloro-5-(di-bromomethyl)phenyl)-5-difluoromethoxy-1-methyl-1H-pyrazole and 6.4 g (36 mmol) of N-bromosuccinimide in 800 ml of tetrachloromethane was irradiated for 2 hours with a 150 W high-pressure mercury lamp and a UV lamp. The solids were then removed by filtration, and the filtrate was concentrated. Silica gel chromatography of the residue (eluent: hexane/ethyl acetate=4:1) gave 2 g of the target product. 1H-NMR (250 MHz, in CDCl3): δ [ppm]=5.87(s,2H); 6.82(t,1H); 7.03(s,1H); 7.52(s,1H); 8.08(s,1H).

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