Diethyl Oxalate → Ethyl 1,4,5,6-tetrahydrocyclopenta[c]pyrazole-3-carboxylate

Participants

Reaction Conditions

Reaction Steps

Cyclopentanone (10.0 g, 118.9 mmol) was taken up in absolute ethanol (30 cm3) and sodium ethoxide (53 cm3, 21% in ethanol, 143 mmol) was added. The resulting solution was stirred under argon for 10 minutes, then diethyl oxalate (19.1 g, 131 mmol) added. Further ethanol (10 cm3) was added and the solution heated at 75° C. for 3 hours and cooled to room temperature. Hydrazine hydrochloride (8.15 g, 119 mmol), taken up in water (20 cm3) was added and the solution heated to 75° C. overnight. Solvent was removed under reduced pressure and the resulting taken up in ethyl acetate (200 cm3) and washed with water (200 cm3), dried (Na2SO4), filtered and solvent removed under reduced pressure to give 1,4,5,6-tetrahydro-cyclopentapyrazole-3-carboxylic acid ethyl ester as an off white solid (16.16 g, 90.0 mmol, 76%). δH (CD3OD): 4.34 (q, 2H, J=7.1, OCH2CH3), 2.78 (t like, 2H, J=7.0), 2.72 (br s, 2H), 2.49 (br s, 2H), 1.36 (t, 3H, J=7.1, OCH2CH3). m/z (ES): 181 [M+H]+.

Provenance & Evidence