Hydrochlorination of spiro(1-pyrazoline-3,1'-cyclopropanes) proceeds regios
electively at the azocyclopropane group to form 3-(2-haloethyl)pyrazoline d
erivatives. If the latter contain a halogen atom in the heterocycle, they a
re readily converted into (2-haloethyl)pyrazole hydrohalides. Bromination o
f 3-cyanospiro(2-pyrazoline-5,1'-cyclopropane) with N-bromosuccinimide at 2
0 degrees C proceeds with retention of the cyclopropane ring to form 3-brom
o-3-cyanospiro(1-pyrazoline-5,1'-cyclopropane), which is converted into (2-
bromoethyl)cyanopyrazole in similar to 60% yield at similar to 20 degrees C
after 3-4 days.