Direct carbohydrate to carbocycle conversions via intramolecular allylation with Et2Zn/Pd(0)

Treatment of 5-vinylpyranosides with Et2Zn and catalytic Pd(0), in the presence of ZnCl2, results in the formation of 5-membered carbocyclic products. This carbohydrate ring-contraction features an intramolecular allylation of a ring-opened carbohydrate aldehyde by an in situ-generated nucleophilic allylzinc species. The stereoselectivity about vinyl and free hydroxyl groups at the newly created stereogenic centers varies from low to moderate while both its extent and sense are found to depend on particular structural features (e.g. the configuration of the starting carbohydrate).