Total synthesis of attenols A and B

The enantioselective synthesis of attenols A and B, cyclic polyethers of marine origin, was accomplished on a semigram scale by using diastereoselective hydroboration, coupling with lithium acetylide, Lindlar reduction and acid-catalyzed acetal formation. The configuration of the remaining undetermined spiro acetal carbon was unambiguously determined to be 11S using this ample supply of attenol A. The antitumor activities of synthetic attenol A were also examined.