Enantioselective synthesis of the C18-C25 segment of lasonolide A by an oxonia-cope prins cascade.

[reaction: see text] A 2-oxonia-Cope Prins cascade was developed that led to a facile and stereoselective synthesis of the C18-C25 segment of lasonolide A. The strategy nicely handles the introduction of the quaternary center in the tetrahydropyran ring, and all of the stereogenic centers in the product arise from a single stereocenter introduced in a catalytic enantioselective reaction.