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9 H ‐Pyrimido[4,5‐ b ]indole‐2,4‐diones. The acid‐catalyzed cyclization of 6‐(phenylhydrazino)uracils
Author(s) -
Wright G. E.
Publication year - 1976
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.5570130324
Subject(s) - chemistry , formic acid , indole test , phenylhydrazine , hydrochloric acid , acid catalysis , medicinal chemistry , catalysis , substituent , barbituric acid , nitrosation , uracil , organic chemistry , hydrolysis , dna , biochemistry
6‐(Phenylhydrazino)uracils undergo facile Fischer‐type cyclization in both N hydrochloric acid and in formic acid at reflux to give 9H‐pyrimido[4,5‐b]indole‐2,4‐diones. Yields appear to be related to substituent effects and side reactions, and these are discussed in light of the mechanism of this reaction. In the reaction of 6‐(phenylhydrazino)uracil itself with hydrochloric acid, the major competing reaction is hydrolysis to barbituric acid and phenylhydrazine, whereas in formic acid a novel cyclization occurs to give I‐phenyl‐3‐carboxamidomethyl‐1,2,4‐triazole as the major product. Nmr spectra of pyrimido[4,5‐b]indole‐2,4‐diones provide interesting examples of peri effects on proton chemical shifts.