Acetonitrile → ethyl 4-fluoro-1-(1-methylethyl)-1H-pyrazole-5-carboxylate

A microwave vial was charged with ethyl 1-(1-methylethyl)-1H-pyrazole-5-carboxylate (0.15 g) and Selectfluor™ (0.38 g) followed by acetonitrile (3 ml) and acetic acid (1 ml). The mixture was heated at 100° C. under microwave irradiation for 180 min. Selectfluor™ (0.076 g) was added and the mixture heated at 100° C. under microwave irradiation for 60 min. Further Selectfluor™ (0.15 g) was added and the mixture heated at 100° C. under microwave irradiation for 60 min. Further Selectfluor (0.38 g) was added and the mixture heated at 100° C. under microwave irradiation for 60 min. The solvent was removed in vacuo and the residue was partitioned between DCM (15 ml) and water (15 ml) and separated using a hydrophobic frit. The aqueous layer was extracted with dichloromethane (2×5 ml) and the combined organic layers were concentrated in vacuo. Purification by chromatography on silica gel (20 g silica cartridge), eluting with a gradient of 0-50% DCM in cyclohexane over 20 minutes gave the title compound (100 mg) as a colourless oil.