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Enazine chemistry II. The mechanism of formation of 1‐( cis ‐3‐phenylpropenyl)‐5‐phenylpyrazole from the pyrolysis of cinnamaldehyde azine
Author(s) -
Stern Robert L.,
Krause Josef G.
Publication year - 1968
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570050220
Subject(s) - chemistry , cinnamaldehyde , intramolecular force , azine , kinetic isotope effect , hydrogen atom abstraction , reaction mechanism , computational chemistry , photochemistry , pyrolysis , kinetic energy , medicinal chemistry , organic chemistry , hydrogen , deuterium , catalysis , physics , quantum mechanics
Abstract The mechanism of pyrazole formation from the thermolysis of α,β‐unsaturated azines has been examined by both kinetic and non‐kinetic methods. The reaction exhibits a large negative entropy of activation, a large primary isotope effect and a positive slope in a Hammett study on cinnamaldehyde derivatives. The reaction was shown to be cleanly intramolecular and was also unaffected by radical traps. A mechanism involving intramolecular 1‐5 abstraction of a proton is presented, which accounts for all of the experimental data.