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1 H and 13 C NMR Study of 1‐Hydrazino‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ a ]pyridazine‐5,8‐diones and ‐1 H ‐pyrazolo[1,2‐ b ]phthalazine‐5,10‐diones and Their Ring‐Chain Tautomerism
Author(s) -
Sinkkonen Jari,
Ovcharenko Vladimir,
Zelenin Kirill N.,
Bezhan Irina P.,
Chakchir Boris A.,
AlAssar Fatema,
Pihlaja Kalevi
Publication year - 2002
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200207)2002:13<2046::aid-ejoc2046>3.0.co;2-c
Subject(s) - phthalazine , tautomer , chemistry , pyridazine , triple bond , carbon 13 nmr , pyrazole , ring (chemistry) , conformational isomerism , proton nmr , stereochemistry , medicinal chemistry , double bond , computational chemistry , organic chemistry , molecule
Treatment of 1‐hydroxy‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ a ]pyridazine‐5,8‐diones and ‐1 H ‐pyrazolo[1,2‐ b ]phthalazine‐5,10‐diones with hydrazides produces corresponding acylhydrazino derivatives. In this work, ten new hydrazino derivatives were synthesized, and their properties were studied by 1 H and 13 C NMR spectroscopy. These compounds exhibited several types of structural variation, including ring‐chain tautomerism, cis ‐ trans isomerism with respect to the substituents in the pyrazole ring, and ( E )/( Z ) rotamerism with respect to the nitrogen−carbon hydrazide bond with partial double‐bond character. In [D 6 ]DMSO, 2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ a ]pyridazine‐5,8‐dione derivatives were found mainly as linear tautomers, whereas 2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ b ]phthalazine‐5,10‐dione derivatives favored cyclic tautomers. For the latter compounds, a six‐component equilibrium was found, consisting of a linear and of cis and trans cyclic tautomers, all of which had two rotamers, ( E ) and ( Z ). (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)