The pyrolysis of 3-vinyl-1-pyrazoline and 3-vinyl-1-pyrazoline-5,5-<i>d</i>₂, and its relation to the vinylcyclopropane to cyclopentene rearrangement

Abstract

The kinetics and products of the pyrolysis of 3-vinyl-1-pyrazoline (1) are described. The pyrolysis of 3-vinyl-1-pyrazoline-5,5-d 2 (II) produces vinylcyclopropane-2,2-d 2 and cyclopentene-4,4-d 2 . The secondary isotope effect has been measured (k H /k D = 1.21 ± 0.03), and the reaction mechanism is interpreted as proceeding through a nitrogen-free intermediate similar to that suggested for the rearrangement of vinylcyclopropane to cyclopentene. At 170° a dramatic change in the product composition occurs, and evidence is presented for a "hot vinylcyclopropane" being produced.