Hydrochloric Acid → tert-butyl 1-(4-chloro-1H-pyrazol-1-yl)cyclopropanecarboxylate

Participants

Reaction Steps

Into a flask was added potassium trimethylsilanolate (20.85 g, 146.31 mmol), 4-chloro-1H-pyrazole (15 g, 146.31 mmol) and 2-methyltetrahydrofuran (400 mL). The mixture was stirred for 5 min followed by the addition of tert-butyl 2,4-dibromobutyrate (27.84 mL, 146.31 mmol) over a period of 20 to 30 seconds. The reaction mixture was stirred for 60 min. Potassium trimethylsilanolate (20.85 g, 146.31 mmol) in 2-methyltetrahydrofuran (80 mL) was added over a period of 5 min. The reaction mixture was stirred for 1 h before adding tert-butyl 2,4-dibromobutyrate (1 mL, 5.3 mmol). After 30 min, an additional portion of tert-butyl 2,4-dibromobutyrate (2 mL, 10.5 mmol) was added. The mixture was stirred for 40 min before adding tert-butyl 2,4-dibromobutyrate (1 mL, 5.3 mmol) and potassium trimethylsilanolate (2 g, 14 mmol). The reaction mixture was stirred for 18 h. Hydrochloric acid (146.31 mL, 146.31 mmol) was added and the mixture was stirred for 5 min. The layers were separated, and the organics were washed with water (200 mL) and concentrated under reduced pressure. Toluene (100 mL) was added and the mixture was concentrated to dryness to afford tert-butyl 1-(4-chloro-1H-pyrazol-1-yl)cyclopropanecarboxylate (45 g). 1H NMR (400 MHz, CDCl3): δ 1.40 (s, 9H), 1.57 (q, 2H), 1.75 (q, 2H), 7.44 (s, 1H), 7.51 (s, 1H); MS (EI+) (M+) 242; GCMS retention time: 2.37 minutes (Method O).

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