General stereoselective synthesis of (E)-exo-alkylidene tetrahydrofurans via base-mediated cyclization of hydroxyl propargylic sulfones

The base-promoted cyclization of a number of phenyl propargylic sulfones possessing a β-hydroxyl group afforded 5-substituted (E)-2- [(benzenesulfonyl)methylene]tetrahydrofurans 3 in >80% yield. The phenyl allenic sulfone, formed by isomerization of the phenyl propargylic sulfone under the basic conditions, is attacked by the internal alkoxide to give an allylic anion which undergoes protonation to form the conjugated exo double bond.