Hydrochloric Acid → 1-cyclopentyl-1H-pyrazole

Participants

Reaction Steps

A mixture of 1,1,3,3-tetramethoxy-propane (13.6 g, 83 mmol) and 1-cyclopentylhydrazine-2-carboxylic acid tert-butyl ester from Ex B18 (16.6 g, 83 mmol) in water (150 mL) was treated with conc HCl (21 mL, 252 mmol) and the resulting mixture was heated at reflux overnight. The reaction mixture was allowed to cool to RT and was extracted with ether. The extracts were washed with brine, dried over anhydrous MgSO4 and filtered. The filtrate was concentrated in vacuo to give 1-cyclopentyl-1H-pyrazole (8.0 g, 71% yield). 1H NMR (400 MHz, CDCl3): δ 7.52 (s, 1 H), 7.43 (s, 1 H), 6.24 (s, 1 H), 4.68 (m, 1 H), 2.20-1.71 (m, 8 H); MS (ESI) m/z: 137.1 [M+H+]

Provenance & Evidence