Asymmetric Syntheses of the Flavonoid Diels–Alder Natural Products Sanggenons C and O

Metal-catalyzed, double Claisen rearrangement of a bis-allyloxyflavone has been utilized to enable a concise synthesis of the hydrobenzofuro3,2-bchromenone core structure of the natural products sanggenon A and sanggenol F. In addition, catalytic, enantioselective 4+2 cycloadditions of 2'-hydroxychalcones have been accomplished using B(OPh)3/BINOL complexes. Asymmetric syntheses of the flavonoid Diels-Alder natural products sanggenons C and O have been achieved employing a stereodivergent reaction of a racemic mixture (stereodivergent RRM) involving 4+2 cycloaddition.