Synthesis of peracetylated C-1-deoxyalditol- and C-glycoside-dipyrranes via dithioacetal derivatives

Dipyrranes bearing peracetylated mono- or disaccharidic C-1-deoxyalditol moieties were prepared from d-galactose, d-glucose, d-mannose, and lactose. A partially hydrolyzed polysaccharide (agarose) was also used as starting material for the synthesis of a disaccharide-containing C-glycoside dipyrrane. These compounds were synthesized as follows: the sugar starting materials were first submitted to a mercaptolysis-acetylation one-pot procedure (EtSH/HCl-Ac2O/pyridine). The resulting peracetylated diethyl dithioacetals were converted into dipyrranes through carbonyl deprotection (H5IO6, THF-Et2O) followed by TFA-catalyzed pyrrole condensation with yields up to 62%. Overall yields from sugar starting materials were up to 49%.