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Facile and Regioselective Synthesis of Substituted 1 H ‐Pyrazolo[3,4‐ b ]quinolines from 2‐Fluorobenzaldehydes and 1 H ‐Pyrazol‐5‐amines
Author(s) -
Szlachcic Paweł,
Kucharek Mateusz,
Jarosz Bożena,
Danel Andrzej,
Stadnicka Katarzyna
Publication year - 2017
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.2751
Subject(s) - regioselectivity , chemistry , dabco , pyrazole , trifluoromethyl , selectivity , fluorine , combinatorial chemistry , condensation , catalysis , medicinal chemistry , organic chemistry , alkyl , physics , thermodynamics
The present article concerns the scope and limitations of the regioselective condensation of 2‐fluorobenzaldehydes with 1 H ‐pyrazol‐5‐amines, leading to the synthesis of substituted 1 H ‐pyrazolo[3,4‐ b ]quinolines ( PQ ), in the presence of a base catalyst (DABCO and 2,4,6‐trimethylpyridine). A method to obtain these nitrogen heterocycles with fluorine or trifluoromethyl substituents in different positions in the carbocyclic ring was developed as a part of a systematic research on the influence of fluorine‐containing substituents on the parameters of PQ . Those compounds, characterized by high‐fluorescence intensity, have been tested as emitters for the organic light‐emitting diodes since 1997. The functionalization of PQ causes changes in various parameters, for example, HOMO and LUMO levels, which are important for the adjustment of fabricated organic light‐emitting diodes. One of the easiest methods of PQ preparation, namely, the condensation of substituted anilines with 5‐chloro‐1 H ‐pyrazole‐4‐carbaldehydes, is not regioselective. The method described in this study allows synthesizing of 1 H ‐pyrazolo[3,4‐ b ]quinolines with good yields and high selectivity – only the expected isomer is obtained. As various different 2‐fluorobenzaldehydes are commercially available, and 1 H ‐pyrazol‐5‐amines with different substituents are easy to prepare, the method could be a good alternative to the already known procedures. All possible mechanisms of the reaction were also thoroughly studied.