The acid and base catalyzed isomerization of some tricyclic 2-pyrazolines with N-Carbamoyl-, N-thiocarbamoyl- and N-phenyl substituents was investigated. Starting from cis or trans 3-H, 3a-H diastereomers, equilibrium mixtures of cis and tl ans diastereomers were prepared which were separated and subsequently studied by H-1 NMR and C-13 NMR spectroscopy. A mechanism for the isomerization of the pyrazolines is suggested, supported by a deuterium exchange at C-3a.
Lorand, Tamas; Szabo, Dezsoe; Foeldesi, Andras, Journal of the Chemical Society. Perkin transactions I, 1985, p. 481 - 486