SYNTHESIS OF 3-SUBSTITUTED (AZIDO, ACYLTHIO, CHLORO OR FLUORO)-2,3-DIDEOXY-D-ERYTHRO-PENTOSES AND 3-METHYL-3-SUBSTITUTED-2,3-DIDEOXY-D-ERYTHRO-PENTOSES

The enantioselective synthesis of 3-substituted and 3-methyl-3-substituted 2,3-dideoxy-D-erythro-pentoses from (3R,4R)-1,1-diethoxy-3,4-epoxypentane-5-ol, (3R,4R)-1,1-diethoxy-3,4-epoxy-3-methylpentane-5-ol and (2R,3R)-2,3-epoxy-5-hexen-1-ol is reported. The key step is cleavage of the oxirane ring by Ti(O-i-Pr)(3)X class reagents followed by selective cyclization of the acyclic acetals to the furanosides. Fluorination with the complex of titanium (IV) iso-propoxide - titanium (IV) fluoride provides an enantioselective synthesis of 3-fluoro-2,3-dideoxy-D-erythro-pentose and 3-fluoro-3-methyl-2,3-dedeoxy-D-erythro-pentose.