First, Atropo-Enantioselective Total Synthesis of the Axially Chiral Phenylanthraquinone Natural Products Knipholone and 6′-O-Methylknipholone

The first stereoselective access to an axially chiral arylanthraquinone, the antimalarial natural product knipholone (3), was achieved by application of the “lactone concept”. Key steps were the intramolecular coupling of the bromoester 1, to give the configurationally unstable biaryl lactone 2, and the enantioselective ring cleavage to form 3.