Synthesis of New 4,4a-Dihydroxanthones via [4+2]-Cycloaddition Reaction

The effect of electronic properties of substituents in the reactants on the [4+2]-cycloaddition of 3-vinyl-chromen-4-ones (dienes) and N -vinylpyrrolidines (dienophiles) has been studied. The conditions determining the formation of 4,4a-dihydroxanthones or benzophenones as the major products have been found. The aromatization of 4,4a-dihydroxanthones via pyran ring opening has been interpreted by quantum chemical calculations. A wide series of new 4,4a-dihydroxanthone and benzophenone derivatives have been isolated.