Total Synthesis and Structural Determination of the Dimeric Tetrahydroxanthone Ascherxanthone A

The first total synthesis of the
dimeric tetrahydroxanthone ascherxanthone
A has been accomplished. This synthetic strategy features (1) enantioselective
intramolecular allylic C–H oxidation to construct a core chiral
chromane, (2) intramolecular aldol reaction/dehydration to form the
enone group, and (3) intermolecular Suzuki–Miyaura coupling
to connect two monomeric tetrahydroxanthones. This synthetic work
allowed us to determine the axial chirality of the 2,2′-biaryl
C–C bond and the absolute configuration of the ascherxanthone
A. This approach should facilitate the preparation of derivatives
and structurally related natural products for medicinal studies.