Synthesis of modified methyl furanosides by intramolecular oxa-Michael reaction followed by Pummerer rearrangement

A new method is described for the synthesis of ribo-furanoses modified at the C3 and C5 positions. The key step is an intramolecular oxa-Michael reaction on a vinyl sulfoxide to install the C2 hydroxy group. The methyl furanosides are obtained by Pummerer rearrangement of the sulfoxide into the corresponding aldehyde, acidic deprotection of the benzylidene acetal, and cyclization