Observation of a 1,5-Silyl-Migration on Fructose

During synthetic studies involving fructose, an unexpected silyl migration was observed - resulting in a sterically more crowded product. 1,4-Silyl migrations have been observed previously taking place in several different carbohydrate derivatives. However, here we report for the first time an apparent base-assisted 1,5-silyl migration in fructose, identified by evidence from X-ray crystallography and 2D-NMR spectroscopy. This novel migration is related to the Brook rearrangement, and appears to be mediated via an anionic, cyclic transition state involving pentavalent silicon.