title: Total Synthesis of Natural Bicyclic Lactones (+)-Dihydrocanadensolide, (+/-)-Avenociolide, and (+/-)-Isoavenociolide via Tungsten-pi-Allyl Complexes.
abstract: A synthetic method using tungsten-pi-allyl compounds is developed for total syntheses of natural bislactones including (+)-dihydrocanadensaolide (2), (+/-)-avenociolide (3), and (+/-)-isoavenociolide (4). Syntheses of these natural compounds are based on a common intermediate, trans-alpha-methylene butyrolactones bearing an anti-homoallylic alcohol. The kep steps in the syntheses involve an intramolecular alkoxycarbonylation of propargyltungsten complexes to yield tungsten-pi,gamma-lactonyl species, followed by condensation of their CpW(NO)I(pi-allyl) derivatives with suitable aldehydes. This new method is very efficient for the synthesis of (+/-)-avenociolide (3) and (+/-)-isoavenociolide (4). Total syntheses of compounds 3 and 4 require only six and three steps, respectively, on the basis of chloropropargyl derivatives.
authors.affiliation: Department of Chemistry, National Tsing-Hua University, Hsinchu, 30043, Taiwan, ROC.
authors.forename: Ming-Jung
authors.initials: MJ
authors.lastname: Chen
authors.forename: Kesavaram
authors.initials: K
authors.lastname: Narkunan
authors.forename: Rai-Shung
authors.initials: RS
authors.lastname: Liu