Dimeric structures of 1,5-anhydro-d-fructose

Upon treatment with acetic anhydride-pyridine, 1,5-anhydro-d-fructose gave the enolone 1,5-anhydro-4-deoxy-d-glycero-hex-3-eno-pyranose-2-ulose as a product of elimination, which is thus available in an overall yield of 25% from d-glucose. During this reaction, acetylated dimers of 1,5-anhydro-d-fructose were formed in a side reaction, whereas these were the only products when acidic acetylation conditions were applied. The acetylated dimers were isolated and served for an unequivocal structural assignment of dimeric forms of 1,5-anhydro-d-fructose 1 by NOESY experiments. Whereas anhydroketose 1 forms dimers in Me2SO and pyridine, its C-4 epimer, 1,5-anhydro-d-tagatose, did not form dimeric structures, neither in non aqueous nor in aqueous solvents.