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Stereoisomerism and Ring‐Chain Tautomerism in 1‐Hydroxy‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ a ]pyridazine‐5,8‐diones and 1‐Hydroxy‐ and 1‐Amino‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ b ]phthalazine‐5,10‐diones
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(200210)2002:20<3447::aid-ejoc3447>3.0.co;2-l
Subject(s) - tautomer , chemistry , pyridazine , phthalazine , ring (chemistry) , stereochemistry , proton nmr , medicinal chemistry , organic chemistry
1‐Hydroxy‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ a ]pyridazine‐5,8diones and 1‐hydroxy‐ and 1‐amino‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ b ]phthalazine‐5,10‐diones were synthesized and their structures studied by NMR and MS methods. All compounds exist in similar cyclic forms in solution, except for 1hydroxy‐1‐methyl‐2,3‐dihydro‐1 H ‐pyrazolo[1,2‐ a ]pyridazine‐5,8‐dione, which displays ring‐chain tautomerism in CDCl 3 solution. The corresponding 3‐methyl‐substituted derivatives exhibit a typical cis / trans isomerism as a result of latent ring‐chain‐ring tautomerism. The structures of stereoisomers concluded from NMR results were additionally confirmed by density functional calculations. Mass spectrometric results indicate open‐chain structures in the gas phase for the molecular ions of the 1‐hydroxy derivatives and cyclic structures for 1‐amino derivatives. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)