Synthesis of l-fructose

Abstract

l-Sorbose ( 1) was converted into methyl 4,6- O-isopropylidene-α- l-sorbofuranoside, which was tosylated to give methyl 4,6- O-isopropylidene-1,3-di- O- p-tolylsulfonyl-α- l-sorbofuranoside. Removal of the isopropylidene protecting group and formation of a 3,4-anhydro-ring afforded methyl 3,4-anhydro-1- O- p-tolyl-sulfonyl-α- l-tagatofuranoside, which was converted into l-fructose ( 7) by acid hydrolysis. In an alternative, facile synthesis, 1 was converted, in the presence of tin(II) chloride as a catalyst, into 1,2:4,6-di- O-isopropylidene-α- l-sorbofuranose. Selective removal of the 4,6- O-isopropylidene group, followed by formation of a 3,4-anhydro ring afforded 3,4-anhydro-1,2- O-isopropylidene-α- l-tagatofuranose. Opening of the anhydro ring by base catalysis and removal of the 1,2- O-isopropylidene group yielded 7.