Perylenequinone Natural Products: Enantioselective Synthesis of the Oxidized Pentacyclic Core

An enantioselective approach to the perylenequinone core found in the mold perylenequinone natural products is outlined. Specifically, the first asymmetric syntheses of helical chiral perylenequinones absent any additional stereogenic centers are described. Key elements of the synthetic venture include a catalytic enantioselective biaryl coupling, a PIFA-induced naphthalene hydroxylation, and a palladium-mediated aromatic decarboxylation. Transfer of the binaphthalene axial stereochemistry to the perylenequinone helical stereochemistry proceeded with good fidelity. Furthermore, the resultant perylenequinones were shown to possess sufficient atropisomeric stability to be viable intermediates in the biogenesis of the perylenequinone natural products. This stability supports the use of the helical axis as a stereochemical relay in synthesis of the natural products containing additional stereochemical centers.