Abstract
A synthetic method using tungsten-π-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-α-methylene butyrolactones bearing an antiohomoallylic alcohol. The kep steps in the syntheses involve an intramolecular alkoxycarbonylation of propargyltungsten complexes to yield tungsten-π,γ-lactonyl species, followed by condensation of their CpW(NO)I(π-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.