4,6-Anhydro derivatives of L-xylo-hexulofuranose

Abstract Crystalline 4,6-anhydro-1- O -benzoyl-2,3- O -isopropylidene-α- L - xylo -hexulofuranose( 16 )has been prepared by treatment of either 1- O -benzoyl-2,3- O -isopropylidene-6- O -tosyl-α- L - xylo -hexulofuranose or the corresponding 6-deoxy-6-iodo compound with anhydrous silver fluoride in pyridine. In a similar manner, 4,6-anhydro-2,3- O -isopropylidene-α- L - xylo -hexulofuranose ( 17 ) was prepared from the 6- O -tosyl and 6-deoxy-6-iodo derivatives of 2,3- O -isopropylidene-α- L - xylo -hexulofuranose. The oxetan 17 , also prepared by debenzoylation of 16 , formed a toluene- p -sulphonate ( 20 ), which was shown to be identical with a compound previously, but incorrectly, reported to be 1,4-anhydro-2,3- O -isopropylidene-6- O -tosyl-α- L - xylo -hexulofuranose. The oxetan structure of the anhydro compounds 16 , 17 , and 20 was proved by three methods. Methylation of 17 afforded a syrupy compound that was identical with 4,6-anhydro-2,3- O -isopropylidene-1- O -methyl-α- L - xylo -hexulofuranose prepared by an unambiguous route. Treatment of 6- O -benzenesulphonyl-2,3- O -isopropylidene-1- O -α- L - xylo -hexulofuranose with base afforded the anhydro compound 20 , thus showing that the tosyl group of 20 was located at C-1. Replacement of this tosyl group with iodide ion, followed by reduction, afforded a C -methyl derivative, the n.m.r. spectrum of which provided unambiguous evidence that the oxetan structure was correct.