Competitive intramolecular nucleophilic aromatic substitution: a new route to coumarins
Abstract
4-Hydroxy-3-(2′-pyridyl)coumarins (4) (R = 6-Cl, H, 6-NO2, 8-NO2) were prepared in moderate to good yields by the intramolecular nucleophilic aromatic substitution reaction of β-ketoesters (I) in refluxing xylenes; evidence for the reversible formation of benzo[c]quinolizinium III from I (X = 4-Cl), with eventual formation of 4 (R = 6-Cl), is also presented.