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 key step involves a NiCl 2 −CrCl 2 -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 room temperature and eventually give the cyclic product 30A possessing the desired cyclic skeleton of 1 in 60% yield. The structure of 30A is determined by X-ray crystallographic analysis. The stereochemistry of Diels−Alder reactions of 7A and another acyclic precursor 7B are discussed. The first total synthesis of (+)-wistarin ( 2 ) is accomplished in 55% yield by iodoether ring formation of 1 and hydrogenolysis of the iodide 33A . Based on the coupling constant in the proton NMR spectrum of 33A, the reported structure 2A is revised to 2B .