Approach to Merosesquiterpenes via Lewis Acid Catalyzed Nazarov-Type Cyclization: Total Synthesis of Akaol A

A Lewis
acid catalyzed Nazarov-type cyclization of arylvinylcarbinol
has been developed for the asymmetric synthesis of carbotetracyclic
core of merosesquiterpenes. The reaction works only in the presence
of 2 mol % of Sn­(OTf)2 and Bi­(OTf)3 in dichloroethane
under elevated temperature. The methodology offers the synthesis of
a variety of enantioenriched arylvinylcarbinols from commercially
available (3aR)-sclareolide 9 in six
steps with an eventual concise total synthesis of marine sesquiterpene
quinol, akaol A (1a).