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Although there was a strong steric effect,isopentenyl and geranyl moieties were successfully introduced into C3 position in flavone skeleton so as to synthesize the 3-isopentenyl flavone and 3-geranyl flavone under two cyclization conditions(AcOH/HCl and concentrated H 2 SO 4 /MeOH) in this report.It was found that the optimum cyclization conditions for 3-isopentenyl flavone and 3-geranyl flavone were,respectively,AcOH/HCl and H 2 SO 4 /MeOH.Furthermore,the donating electron ability is in the sequence 3-geranyl flavone>3-isopentenyl flavone according to the density functional theory(DFT) calculations,suggesting the longer alkyl chain at 3-position would be more favorable for enhancing the donating electron ability.The present synthetic routes might reveal potential applicability in our continued studies on the total syntheses of other natural 3-alkyl flavonoids.
Although there was a strong steric effect, isopentenyl and geranyl moieties were successfully introduced into C3 position in flavone skeleton so as to synthesize the 3-isopentenyl flavone and 3-geranyl flavone under two cyclization conditions (AcOH / HCl and concentrated H 2 SO 4 / MeOH) in this report. It was found that the optimum cyclization conditions for 3-isopentenyl flavone and 3-geranyl flavone were, respectively, AcOH / HC1 and H2SO4 / MeOH.Furthermore, the donating electron ability is in the sequence 3 -geranyl flavone> 3-isopentenyl flavone according to the density functional theory (DFT) calculations, suggesting that longer alkyl chain at 3-position would be more favorable for enhancing the donating electron ability. the present synthetic routes might reveal potential applicability in our continued studies on the total syntheses of other natural 3-alkyl flavonoids.