Stereoselective synthesis of both tetrahydropyran rings of the antitumor macrolide, (-)-lasonolide A.

Stereoselective syntheses of both functionalized tetrahydropyran subunits of (-)-lasonolide A are described. These tetrahydropyran rings were constructed using catalytic asymmetric hetero Diels-Alder reactions as the key steps. The C22 quaternary stereocenter present in the upper tetrahydropyran ring was constructed by a stereoselective alkylation, and the C9 hydroxy stereochemistry of the bottom tetrahydropyran was constructed by a stereoselective epoxidation followed by a regioselective epoxide opening reaction.