Concise Total Syntheses of (−)-Ohioensin A, Putative (+)-Ohioensin C, (+)-Myristinins A and B/C, and (+)-Caesalpinflavan A

Abstract

The ohioensins represent a distinct class of polycyclic benzonaphthoxanthenone natural products that share structural similarities with flavonoids. Herein, we disclose a unified synthetic approach that culminates in the first concise enantioselective total syntheses of (−)-ohioensin A and putative (+)-ohioensin C, as well as the flavonoids (+)-myristinins A and B/C and (+)-caesalpinflavan A. The synthetic strategy hinges on the development of novel methodologies, including a chiral biphenol-catalyzed enantioselective conjugate addition of alkenyl and aryl boronic acids to 2-hydroxynitrostyrenes, a stereodivergent cyclization to procure both cis- or trans-2,4-disubstituted benzodihydropyrans, and an intramolecular deaminative aromatic homolytic substitution.