DIMERIC STRUCTURES OF 1,5-ANHYDRO-D-FRUCTOSE

Upon treatment with acetic anhydride-pyridine, 1,5-anhydro-D-fructose gave the enolone nhydro-4-deoxy-D-glycero-hex-3-enopyranose-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. Th e acetylated dimers were isolated and served for an unequivocal struct ural assignment of dimeric forms of 1,5-anhydro-D-fructose 1 by NOESY experiments. Whereas anhydroketose 1 forms dimers in Me2SO and pyridin e, its C-4 epimer, 1,5-anhydro-D-tagatose, did not form dimeric struct ures, neither in non aqueous nor in aqueous solvents. (C) 1998 Elsevie r Science Ltd. All rights reserved.