Synthetic studies of antitumor macrolide laulimalide: a stereoselective synthesis of the C17-C28 segment.

A stereoselective synthesis of the C17-C28 segment of the potent antitumor macrolide, laulimalide has been accomplished. The key steps are a ring-closing olefin metathesis to construct the dihydropyran unit, nucleophilic addition of an alkynyl anion to the Weinreb amide, stereoselective reduction of the resulting ketone to set the C20-hydroxyl stereochemistry, and elaboration of the C21-C22 trans-olefin geometry.