Synthesis of the lower subunit of rhizoxin

Full details of a study to a synthesis of the optically active C13-C26 lower subunit of rhizoxin including the side-chain chromophore characteristic of the full class of antimitotic agents are described. A key element of the synthesis is the stereoselective introduction of the C18-C19 trisubstituted olefin through use of a Wadsworth-Horner-Emmons condensation of 3 with β-keto phosphonate 38 bearing resident functionality suitable for the diastereoselective introduction of C15-C17 employing a hydroxyl-directed reduction of the resultant β-hydroxyl ketone