Reactions of spirocyclopropane-containing 1- and 2-pyrazolines with electrophilic reagents

Article abstract of DOI:10.1007/BF02494777

Hydrochlorination of spiro(1-pyrazoline-3, 1′-cyclopropanes) proceeds regioselectively at the azocyclopropane group to form 3-(2-haloethyl)pyrazoline derivatives. If the latter contain a halogen atom in the heterocycle, they are readily converted into (2-haloethyl)pyrazole hydrohalides. Bromination of 3-cyanospiro(2-pyrazoline-5,1′-cyclopropane) with N-bromosuccinimide at 20 °C proceeds with retention of the cyclopropane ring to form 3-bromo-3-cyanospiro(1-pyrazoline-5,1′-cyclopropane), which is converted into (2-bromoethyl)cyanopyrazole in ～60% yield at ～20 °C after 3 - 4 days.