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0 °C

To a solution of 4-bromo-5-methyl-3-trifluoromethyl-1H-pyrazole (1.4 g, 6.2 mmol, 1.0 equiv) in chloroform (31 ml) was added p-toluene sulphonic acid monohydrate (118 mg, 0.62 mmol, 0.1 equiv). The solution was cooled to 0° C. and 3,4-dihydro-2H-pyran (0.85 ml, 9.3 mmol, 1.5 equiv) was added drop-wise over 5 minutes. The mixture was allowed to warm to room temperature for 1 hour and the solvents were removed under reduced pressure. The crude mixture was purified by column chromatography (SiO2), eluting with 0→25% EtOAc-petrol over a linear gradient to afford the title compound 1.4 g (59%), LCMS (PS-A) Rt 3.72 min [M+H]+ 314.

1. temperatureto warm to room temperature for 1 hour
2. customthe solvents were removed under reduced pressure
3. customThe crude mixture was purified by column chromatography (SiO2)
4. washeluting with 0→25% EtOAc-petrol over a linear gradient