TOTAL SYNTHESIS OF (-)-IRCINIANIN AND (-WISTARIN())

(-)-Ircinianin (1), a cyclic furanosesterterpenetetronic acid isolated from a marine sponge (genus Ircinia), is synthesized in 17 steps from (S)-2-methylpropane-1,3-diol mono THP ether 10 and 3-furfural. The ke y step involves a NiCl2-CrCl2-mediated coupling reaction of iodotriene 9 with chiral aldehyde 8 in DMSO and subsequent intramolecular Diels- Alder reaction in one pot. Both reactions proceed very smoothly at roo m temperature and eventually give the cyclic product 30A possessing th e desired cyclic skeleton of 1 in 60% yield. The structure of 30A is d etermined by X-ray crystallographic analysis. The stereochemistry of D iels-Alder reactions of 7A and another acyclic precursor 7B are discus sed. The first total synthesis of(+)-wistarin (2) is accomplished in 5 5% yield by iodoether ring formation of 1 and hydrogenolysis of the io dide 33A. Based on the coupling constant in the proton NMR spectrum of 33A, the reported structure 2A is revised to 2B.