Synthesis of 6H-[1]Benzofuro[3,2-b]chromeno[4,3-d]pyridin-6-ones 7a-h (General Method).
A mixture of 4-(3-amino-2-benzofuranyl)coumarin 2a,f or 2i (5 mmol), aromatic aldehyde (5 mmol) or 37%
formalin (1 ml, 10 mmol), and p-toluenesulfonic acid (10 mg) in acetic acid (50 ml) was heated for 2-3 h at
60-70°C. The solution, which turns red, was stirred with the introduction of an air stream until there was no
further oxidation and it assums a yellowish-hue (the end of the reaction was determined chromatographically) or
4 mmol CrO3 was added and the mixture was stirred with heating for 60-90 min. The reaction mixture was
cooled and diluted by adding cold water. The precipitate formed was filtered off, dried, and crystallized from
DMF or dioxane.
Evaporation of the mother liquor after the crystallization of 7a gave pyridone 6a.
7-(3,4-Dimethoxyphenyl)-2-ethyl-7,8-dihydro-6H-benzofuro[3,2-b]chromeno[4,3-d]pyridin-6-one
1
(6a). The yield of 6 was 15 mg, C28H23NO5; mp 247-248°C. H NMR spectrum, δ, ppm (J, Hz): 1.28 (3H, t,
J = 7.4, 2-CH3CH2); 2.76 (2H, m, 2-CH3CH2); 3.65, 3.67 (6H, 2s, 3'-OCH3 and 4'-OCH3); 5.92 (1H, d, J = 3.4,
H-7); 6.82, 7.08 (3H, 2m, H-2', H-5', and H-6'); 7.34 (2H, m, H-4 and H-10); 7.53 (2H, m, H-3 and H-11); 7.69
(1H, m, H-12); 7.90 (1H, m, H-9); 8.37 (1H, d, J = 3.4, 8-NH); 8.47 (1H, m, H-1).
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