SYNTHESIS OF THE PSEUDOPTERANE AND FURANOCEMBRANE RING-SYSTEMS BY INTRAANNULAR CYCLIZATION OF BETA-ALKYNYL AND GAMMA-ALKYNYL ALLYLIC ALCOHOLS

The prototype pseudopterane and furanocembrane systems 15 and 26 were prepared through a ''furan last'' approach. The former was obtained in 64% yield upon treatment of the 12-membered beta-alkynyl allylic alcohol 14 with KO-t-Bu and 18-c-6 in THF-t-BuOH. The latter was formed in 88% yield from the 14-membered gamma-alkynyl allylic alcohol 25 under comparable conditions. The carbocyclic precursors to these allylic alcohols, 11 and 24, were secured through intramolecular Horner-Emmons condensation of keto phosphonates 10 and 23, respectively, under Masamune-Roush conditions.