SOME INTRAMOLECULAR REARRANGEMENTS WHEN PENTOFURANOSES ARE TREATED WITH DIETHYLAMINOSULFUR TRIFLUORIDE (DAST)

Treatment of methyl 2,3-O-isopropylidene-beta-D-ribofuranoside with DAST gave a good yield of 2,3-O-isopropylidene-5-0-methyl-beta-D-ribofuranosyl fluoride in which the methoxy group had migrated from C-1 --> C-5 and been replaced with retention of configuration by fluorine. The corresponding aldehyde when treated under similar conditions underwent a similar migration to give 5-deoxy-5-fluoro-2,3-O-isopropylidene-5-O-methyl-beta-D-ribofuranosyl fluoride. A similar migration occurred with methyl 2',3'-di-O-acetyl-beta-D-ribofuranoside and with acetyl 2,3-O-isopropylidene-D-ribofuranose but not with 1,2,3-tri-O-acetyl-D-ribofuranose. Thus the migration depends upon the migratory aptitude of the substituent at C-1 and the conformation of the furanose ring. Two ribofuranosyl fluorides were used as starting materials from which to make nucleosides by the method of Noyori and Hayoshi