Common and specific features of the Michael condensation in the series of 3-R-3H-furan-2-ones

The Michael condensation in the series of 5-aryl-3H-furan-2-ones with chalcones containing electron-donating substituents was studied. In the case of alpha,beta-unsaturated ketones containing an electron-donating substituent, the reaction does not stop at the stage of formation of 1,5-dicarbonyl compounds but is accompanied by intramolecular cycloclehydration yielding a new series of furo[2,3-b]-4H-pyrans. A mechanism of formation of these products was suggested. The structure of reaction products was proved by IR and H-1 NMR spectroscopy.