ChemInform Abstract: AZOLE 78. MITT. NEUE SYNTH. VON 3‐PYRAZOLINEN, ISOLIERUNG VON INTERMEDIAEREN 3‐HYDROXY‐PYRAZOLIDINEN

Abstract

Die durch Reaktion des Hydrazins (II) mit den Zimtaldehyden (I) in Äthanol in Gegenwart von HCl in situ gebildeten Pyrazoliniumsalze (III) geben mit konz. Alkali die 3‐Pyrazoline (IV) (47‐50% Ausbeute), während mit verdünntem Alkali die Hydroxypyrazolidine (V) entstehen.

3-Pyrazolines (2,3-dihydro-1H-pyrazoles): synthesis, reactivity, and physical and biological properties

“…23 The transformation of 13 into 12 by the action of NaOH involves a 3-hydroxypyrazolidine 14 (Figure 3). 24,25 The mechanism for the formation of 13 is the same as that for 2-pyrazolines. For a long time 26 it was not clear which of the two NC bonds was formed first, i.e., 17 or 21 (Scheme 6).…”

“…The Petrus group published a paper that contained some examples of endo/exo tautomerism (Scheme 45) where only one tautomer, 172a and 173b, was observed. 149 Scheme 45. The effect of amide substituents on endo/exo tautomerism.…”

“…161 The fact that the minor tautomer is the most reactive is known as the Gustafson paradox. 149,161 Scheme 51. Reactivity of 3-pyrazolines as enamines.…”