Protective group-free synthesis of 3,4-dihydroxytetrahydrofurans from carbohydrates: formal total synthesis of sphydrofuran.

Carbohydrates are taking a more prominent role in chemistry as an environmentally benign chemical feedstock. However, major efforts are still required to convert unprotected carbohydrates into high-value building blocks. We have investigated the protective group-free Wittig reaction and subsequential acid catalyzed intramolecular cyclization of unprotected carbohydrates to obtain 3,4-dihydroxytetrafurans. In this process, we have found that, when using Lewis acids and poly-alcohol substrates, additional attention should always be given to the catalytic nature of the acid as it might involve its ligands instead of the metal. Furthermore, we illustrate the viability of the concept by a straightforward formal total synthesis of the natural product sphydrofuran from d-xylose.