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A suspension of methyltriphenylphosphonium bromide (58.92 g, 162 mmol) in tetrahydrofuran (400 ml) was treated at room temperature with potassium tert-butylate (18.51 g, 162 mmol), and the mixture was stirred for 30 minutes. While cooling with ice, a solution of 1-(5-bromo-2-fluoro-phenyl)-ethanone [CAS No. 198477-83-3] (29.23 g, 135 mmol) in tetrahydrofuran (50 ml) was added. Thereafter, the mixture was warmed to room temperature and stirred for 1.5 hours. For the workup, the mixture was treated with ethyl acetate (650 ml) extracted with water (450 ml). The organic layer was separated, washed with brine (220 ml), dried over sodium sulfate and evaporated at reduced pressure. After chromatography on silica gel using a mixture of hexane and ethyl acetate as the eluent, the 4-bromo-1-fluoro-2-isopropenyl-benzene (intermediate C2A) was obtained as a yellow oil (28.49 g, 98% of theory). Rf: 0.7 (silica gel; eluent: heptane).

1. temperatureWhile cooling with ice
2. stirringstirred for 1.5 hours
3. extractionextracted with water (450 ml)
4. customThe organic layer was separated
5. washwashed with brine (220 ml)
6. dry with materialdried over sodium sulfate
7. customevaporated at reduced pressure
8. additionAfter chromatography on silica gel using a mixture of hexane and ethyl acetate as the eluent