SYNTHESIS OF 1,2-ANHYDRO-3,4,5-TRI-O-BENZYL-BETA-D-FRUCTOPYRANOSE

A synthesis of the anomeric spiro-epoxide 15 from D-fructose, in 7-steps in an overall 13% yield, is described. The key intermediate in the synthesis, 3,4,5-tri-O-benzyl-1-deoxy-1-iodo-beta-D-fructopyranose (14), was prepared from the corresponding methyl (14), was prepared from the corresponding methyl fructopyranoside by reaction with the iodine-triphenylphosphine-imidazole reagent complex, followed by acid hydrolysis. Ring closure of the iodohydrin 14 was achieved under extremely mild conditions on treatment with silver(I) oxide in anhydrous THF. The C-13 NMR spectrum of 15 exhibited a large upfield shift of the resonances assigned to C-1 and C-2, indicative of an oxirane ring involving these two carbon atoms.