Reaction Of 3-formylchromones Research Articles

Reaction of 3-formylchromone with methyl- and methylene-active azocycles

The reaction of 3-formylchromone with quaternary salts of nitrogen heterocycles containing active methyl or methylene groups was investigated. It is shown that the compounds obtained can be used in the synthesis of merocyanine dyes containing an o-hydroxybenzoyl substituent in the polymethine chain. Dicarbocyanines with such a substituent were not isolated, evidently because of the high electrophilicity of the polymethine chain and the ease of formation of a six-membered heteroring.

Heterodiene cycloadditions of 3-acylchromones with enol ethers

3-Formylchromones behave as heterodienes in stereoselective (4π+ 2π)cycloadditions with enol ethers at 20 °C, the formal endo-addition product predominating. An electron-donor substituent (OH, OMe) in the aromatic ring retards the reaction and slightly increases endo selectivity, while an electron-withdrawing group (NO2) has the reverse effect. 3-Acetyl- and 3-benzoyl-chromone react much more slowly but with similar stereoselectivity. The reaction of 3-formylchromone (3a) with t-butoxyethene is almost non-selective, while with dihydropyran it forms novel isomeric pyrano[2′,3′ : 6,5]pyrano[4,3-b][1]benzopyranones (23) and (24) in which the enol ether geometry is retained. Reaction rates and stereoselectivity vary slightly with solvent and temperature, and the results indicate a concerted cycloaddition mechanism with kinetically controlled stereoselection.