Trifluoroacetic acid → tert-butyl 4,5-dihydro-1H-pyrazole-5-carboxylate

Participants

Reaction Conditions

Reaction Steps

A 1 L rb flask was charged with t-butylacrylate (11.33 mL, 78 mmol) in toluene (100 mL) and tetrahydrofuran (THF) (100 mL). To this was added via addition funnel TMS-diazomethane (50.5 mL, 101 mmol) dropwise over 25 minutes under N2. The reaction mixture was stirred at 25° C. for 4.5 h. The solvent was evaporated under reduced pressure. The crude product was dissolved in dichloromethane (70 mL) and cooled in an ice bath. To this solution was added TFA (7.21 mL, 94 mmol.) dissolved in 30 mL of dichloromethane via addition funnel. After addition was complete the mixture was stirred at 25° C. for 0.5 h. The solvent was evaporated and the residue was neutralized by the addition of sat. NaHCO3 and extracted into DCM. The organic layer was dried over Na2SO4, filtered, and concentrated to give the crude product which was purified by automated silica gel column chromatography (column: 120 g, 0-38% ethyl acetate in hexane, 34 min). The solvent was removed under reduced pressure to afford 8 g (47 mmol, 60%) of 1,1-dimethylethyl 4,5-dihydro-1H-pyrazole-5-carboxylate as pale yellow oil. LC-MS (ES) m/e 171.1 (M+H)+.

Provenance & Evidence