Permanganate oxidation of 1,5,9-trienes: Stereoselective synthesis of tetrahydrofuran-containing fragments

Permanganate oxidation of farnesoate esters 12a-d afforded perhydro-2,2'-bifuranyl compounds 16a-d, with control of relative stereochemistry at four new stereocenters. Subsequent oxidative cleavage of 16a-d then provided tetrahydrofuran-containing fragments 17a-d, one of them 17b possessing the same relative stereochemistry present in the C13-C21 portion of the polyether antibiotic semduramycin (1). Control of the absolute stereochemistry was achieved through the use of the Oppolzer sultam chiral auxiliary. The requisite starting trienes were prepared stereoselectively in just three steps from geranyl chloride or neryl chloride, providing a short and versatile route to polyether fragments.