Enantioselective and Collective Total Syntheses of Xanthanolides

An enantioselective synthesis of (+)-8-epi-xanthatin has been achieved, hinging on a chiral phosphoric acid-catalyzed tandem allylboration/lactonization reaction. With (+)-8-epi-xanthatin as precursor, the collective syntheses of a series of synthetically challenging xanthanolides were also accomplished. Among them, xanthipungolide, one of the most complicated xanthanolide monomers, was accessed through a bio-inspired tandem double bond isomerization/6π electronic cyclization/intramolecular Diels-Alder reaction, and pungiolides A, B, D, E, and L-N, a group of xanthanolide dimers, were assembled through a bio-inspired Diels-Alder dimerization followed by late-stage diversification.