Practical Synthesis of 4′-Thioribonucleosides from L-Arabinose via Novel Reductive Ring-Contraction Reaction and Pummerer-Type Thioglycosylation

The detailed practical synthesis of 4′-thionucleosides starting from L-arabinose is described here. 1,4-Anhydro-2,3-O-isopropylidene-4-thioribitol, which is the key intermediate for the synthesis of 4′-thionucleosides, is obtained from L-arabinose in several steps, including a novel reductive ring-contraction reaction. After oxidation of the key intermediate, the sulfoxide is subjected to Pummerer-type thioglycosylation in the presence of persilylated nucleobases to obtain the 4′-thioribonucleosides in good yield and β-selectively. © 2017 by John Wiley & Sons, Inc.