Synthesis of nonadjacently linked tetrahydrofurans: an iodoetherification and olefin metathesis approach

reaction: see text] A convergent approach to the synthesis of the bis-tetrahydrofuran (THF) components of the nonadjacently linked THF-containing acetogenins is illustrated in the synthesis of 2, a potential intermediate for the antitumor agent bullatanocin (squamostatin C). The plan centers on the olefin cross-metathesis of THF allylic alcohol derivatives 3 and 4 as the key segment coupling step and the assembly of 3 and 4 through the iodoetherification of 1,2-O-isopropylidene-5-alkene precursors.