Synthesis of higher carbon sugars. Unexpected rearrangement of higher sugar allylic alcohols

Coupling of a sugar phosphonate with a sugar aldehyde afforded a C13-higher sugar enone. Reduction of the carbonyl function provided both stereoisomeric allylic alcohols. Inversion of the configuration at the carbinol centre in these derivatives did not yield the expected SN2 product, but proceeded with rearrangement to the tetrahydrofuran derivative.