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

✍ Scribed by Leslie W. Deady; Thomas Rodemann

Publisher
Journal of Heterocyclic Chemistry
Year
2001
Tongue
English
Weight
57 KB
Volume
38
Category
Article
ISSN
0022-152X

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✦ Synopsis

Abstract

Homophthalic acid and its pyrido and 8‐methylquinolino analogues with dimethylformamide/phosphoryl chloride at 0° 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‐5__H__‐pyrano[4,3‐b]pyridine‐8‐carbox‐aldehyde (5b) and 3‐hydroxy‐6‐methyl‐1‐oxo‐1__H__‐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‐1__H__‐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.

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