General one-step synthesis of free hexofuranosyl 1-phosphates using unprotected 1-thioimidoyl hexofuranosides

A general one-step strategy is developed for the synthesis of hexofuranosyl 1-phosphates starting from new unprotected glycofuranosyl donors. It required first the preparation of new 1-thiohexofuranosides bearing a thioimidoyl heterocycle as a leaving group. The presence of sulfur and/or nitrogen atom(s) on the aglycon allowed remote activation of these thioglycofuranosides by anhydrous phosphoric acid and led to the target phosphates 9, 27, 29, and 30 in good to excellent selectivities and, more importantly, with very limited or no ring expansion. Moreover, this one-step phosphorylation reaction could be significantly improved by avoiding any tedious protecting group manipulations on negatively charged compounds and by focusing on a simple but general procedure of purification. This approach was applied to the diastereocontrolled synthesis of d-galacto- and d-glucofuranosyl 1-phosphates and also to the preparation of rare epimer and/or deoxy counterparts, that is, d-manno- and d-fucofuranosyl derivatives.