Regioselective Synthesis of L-Idopyranuronic Acid Derivatives: Intermolecular Aglycon Transfer of Dithioacetal Under Standard Glycosylation Conditions

C-1-thioacetalization of L-idofuranurono-6,3-lactone followed by regioselective p-methoxybenzylidenation at C-2 and C-4 gave the hydroxylactones 4 and 19, which were protected at C-5 with TBDMS. Lactone ring opening with methylamine followed by regioselective reductive cleavage of the 1,3-dioxane furnished acceptors 9 and 24. Intermolecular ethyl and phenyl thio group transfers were observed during the attempted preparation of disaccharide 35 through coupling reactions of either 9 or 24 with trichloroacetimidate donor 33, leading to the formation of thioglycoside of donor 33 and the thioglycoside of acceptors 9 or 24 in the furanose form. This intermolecular aglycon transfer was investigated under various glycosylation conditions. Finally, the free 4-hydroxyl groups in acceptors 9 and 24 were acetylated. Desilylation at C-5 followed by ring closure with mercuric salts afforded, in both cases, the IdopA donor and/or acceptor precursor 16.