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Studies on 2,1‐benzisoxazoles. Behaviour towards electrophilic substitution and cycloaddition reactions
Author(s) -
Boruah R. C.,
Sandhu J. S.,
Thyagarajan G.
Publication year - 1981
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.5570180604
Subject(s) - chemistry , nitration , ring (chemistry) , electrophile , nitro , electrophilic substitution , cycloaddition , medicinal chemistry , dimethyl acetylenedicarboxylate , mindo , aryl , stereochemistry , organic chemistry , catalysis , molecule , alkyl
The behaviour of 2,1‐benzisoxazoles (anthranils) towards electrophilic substitutions has been studied. Nitration of 5‐chloro‐2,1‐benzisoxazole (VII) exclusively gives 4‐nitro‐5‐chloro‐2,1‐benzisoxazole (XII). However, 5‐chloro‐3‐phenyl‐2,1‐benzisoxazole (VIII) gives dinitrated products XIII, one nitro group entering at position C 7 instead of C 4 of the carbocyclic ring and the other at the 4′ position of the 3‐aryl ring. When 6‐nitro‐3‐carbalkoxy‐2,1‐benzisoxazoles (X and XI) are nitrated, 4‐nitroisomers XV and XVI are obtained exclusively. The substituents already present in the carbocyclic ring exert decisive directing influence. While the parent 2,1‐benzisoxazole (Ia) fails to react with dimethyl acetylenedicarboxylate, 6‐nitro‐2,1‐benzisoxazole (XVII) and 5‐chloro‐2,1‐benzisoxazole (VII) react to give 1,4‐cycloadducts XIX and XX, respectively. These results suggest that 2,1‐benzisoxazoles possess benzenoid as well as ortho ‐quinonoid character.