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Cycloaddition of α‐Chloroformylarylhydrazines' with Pyridines Afford 2‐Aryl‐2 H ‐[1,2,4]triazolo[4,3‐a]pyridin‐3‐Ones
Author(s) -
Chiu ChunYen,
Kuo ChaoNan,
Kuo WenFa,
Yeh MouYung
Publication year - 2001
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.200100168
Subject(s) - cycloaddition , chemistry , substituent , steric effects , aryl , pyridine , ring (chemistry) , medicinal chemistry , inductive effect , polar effect , stereochemistry , organic chemistry , catalysis , alkyl
2‐Aryl‐2 H ‐[1,2,4]triazolo[4,3‐ a ]pyridin‐3‐ones 4 were synthesized by cycloaddition of α‐chloroformylarylhydrazines 7 with pyridines 1 . The inductive and mesomeric effects of substituents on pyridines were also investigated in this study. In reactions of 3‐substituted pyridines bearing a π‐electron‐donating substituent, the ortho site, C(2), of the pyridine ring is more favored for cycloaddition than the para site, C(6). As the substituent is a σ‐electron‐donating group, the cycloaddition only occurs on the ortho position. For reactions of 2‐substituted pyridines, however, cycloadditions were controlled solely by inductive effect, regard less of mesomeric effect. Only when the substituent is an electron‐donating group, would the cycloaddition proceed to afford expected cycloadducts. Further more, it is found that the inductive effect plays a more important role than the steric effect for reactions using 2‐substituted pyridines.