A new approach to C‐branched monosaccharides by the stereoselective hydrodesulfurization of methyl 4,6‐O‐benzylidene‐3‐[bis(methylthio)‐methylene]‐3‐deoxy‐α‐D‐erythro‐hexopyranosid‐2‐ulose

The stereoselective reduction of methyl 4,6‐ O ‐benzylidene‐3‐[bis(methylthio)methylene]‐3‐deoxy‐α‐ D ‐ erythro ‐hexopyranosid‐2‐ulose 1 with sodium tetrahydridoborate and tributyltin hydride, respectively, to (Z)‐configured 4 is described. The increased reactivity of 4 compared to 1 is reflected in several substitution reactions resulting in the displacement of the methylthio group by different N nucleophiles. The substitution products 6–8 were stereoselectively obtained as (Z) isomers. Pyrano[3,4‐ c ]pyrazole derivatives 3 and 10 were prepared by treatment of 1 and 4 , respectively, with hydrazine hydrate.