Synthetic route for optically active tetracyclic hexahydrobenzofurobenzopyran skeleton of bisabosquals

In this study, for the first time, we synthesized the optically active form of the hexahydrobenzofurobenzopyran ring, which is found in naturally occurring bisabosquals. This synthetic route involved three key steps: (i) induction of chirality into the allylic alcohol moiety via the Suzuki-Miyaura cross-coupling of an aryl iodide and a chiral alkenyl borate; (ii) transfer of chirality from the optically active allylic ester to the resultant carboxylic acid formed via the Ireland-Claisen rearrangement; and (iii) stepwise construction of the hexahydrobenzofurobenzopyran skeleton from a cyclohexene substrate via an acid-mediated fused furan/pyran ring formation. Using our synthetic route, we obtained both the racemic and optically active hexahydrobenzofurobenzopyrans.