3-Substituted-4-hydroxycoumarins have been recently identified as active no
npeptidic HIV pretense inhibitors. In order to get more potent inhibitors,
synthesis of a number of 3-substituted-4-hydroxycoumarins have been designe
d. Nucleophilicity of C-3 in 4-hydroxycoumarin is exploited by reacting wit
h an electrophile3-carbethoxycoumarin to achieve a new C-3 substituted-4-hy
droxycoumarin. But the product identified is a benzopyranodicoumarin (2), w
hich is also obtained by the reaction of 4-hydroxycoumarin with salicylalde
hyde. However, the reaction of 4-hydroxycoumarin with a number of 2-oxygena
ted aldehydes 4b-e affords dicoumarols (5a-d) only. On the contrary, with 2
,4,5-trimethoxybenzaldehyde (4f), a benzopyranodicoumarin (6a) is formed. T
he reaction of 4-hydroxycoumarin with 6-bromo-3,4-methylenedioxybenzaldehyd
e (4g) and 6-bromo-3,4-dimethoxybenzaldehyde (4h), when treated separately,
furnisher benzopyranodicoumarin (Gb) and benzopyranocoumarin (7) respectiv
ely. In both the eases, unusual nucleophilic aromatic substitution of bromi
ne occurs in electron-rich aromatic systems without any catalyst.