Acid-promoted reaction of cyclic allylic diols with carbonyl compounds. Stereoselective ring-enlarging tetrahydrofuran annulations

A wide variety of cis-fused hexahydrocyclopenta [b] furan-4-ones (3, n=0), hexahydro-4(2H)-benzofuranones (3, n=1), and octahydrocyclohepta [b] furan-4-ones (3, n=2) can be prepared with high levels of stereocontrol by the title reaction. The scope and limitations of this powerful new method for assembling polycyclic ethers are explored in detail. Conformational analysis of potential oxabicyclo [4.4.0] decanyl, oxabicyclo [4.3.0] nonanyl, and oxabicyclo [4.2.0] octanyl cation intermediates allows the stereochemical outcome of the title reaction to be predicted