Bio-inspired formal total synthesis of (±)-bisabosqual A

A new approach was developed to construct a hexahydrobenzofurobenzopyran ring system (6/6/5/6) by an oxa-[3 + 3] cycloaddition, intramolecular hetero-Diels-Alder reaction, oxidative aromatization, and oxidative cyclization cascade starting from 5-(hydroxymethyl)cyclohexane-1,3-dione and (2E,6E)-farnesal. This strategy provides a new solution for preparing tetracyclic hexahydrobenzofurobenzopyran rings with different functional groups at C-3 '-C4 '. As a synthetic application, the bio-inspired formal total synthesis of bisabosqual A was achieved.