The reaction of homophthalic acid and some aza analogues with Vilsmeier reagent: a reinvestigation

Homophthalic acid and its pyrido and 8-methylquinolino analogues with dimethylformamide/phosphoryl chloride at 0 degrees give the appropriate 4-(dimethylaminomethylene)isochroman-1,3-dione (2a, 2b, 2c, respectively). Under the literature conditions for conversion of 2a to 2-methyl-1-oxo-1,2-dihydroi...

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Bibliographic Details
Published inJournal of heterocyclic chemistry Vol. 38; no. 5; pp. 1185 - 1190
Main Authors Deady, LW, Rodemann, T
Format Journal Article
LanguageEnglish
Published HOBOKEN Wiley 01.09.2001
Subjects
Chemistry
Chemistry, Organic
Physical Sciences
Science & Technology
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Summary:Homophthalic acid and its pyrido and 8-methylquinolino analogues with dimethylformamide/phosphoryl chloride at 0 degrees give the appropriate 4-(dimethylaminomethylene)isochroman-1,3-dione (2a, 2b, 2c, respectively). Under the literature conditions for conversion of 2a to 2-methyl-1-oxo-1,2-dihydroisoquinoline-4-carboxylic acid (3a), the aza analogues give instead 7-hydroxy-5-oxo-5H-pyrano[4,3-b]pyridine-8-carboxaldehyde (5b) and 3-hydroxy-6-methyl-1-oxo-1H-pyrano[4,3-b]quinoline-4-carboxaldehyde (5c), respectively. Modified conditions were required to isolate analogues 3b and 3c. Further, while reaction of 2a with hydrogen chloride in methanol gave the known change to methyl 1-oxo-1H-isochromene-4-carboxylate (4), 2b and 2c gave only products of oxa-ring cleavage. Methyl 2-(cis-2-hydroxyvinyl)-8-methylquinoline-3-carboxylate (8) was the main product from 2c, while a novel quinolizinium species (11) was formed in good yield from 2b.
ISSN:0022-152X
DOI:10.1002/jhet.5570380524