Stable D-xylose ditriflate in a new, divergent syntheses of dihydroxy prolines and pyrrolidines

Carbohydrates constitute an abundant source of useful scaffolds for the synthesis of highly functionalized carbo- and heterocycles.¹ They provide the stereogenic centers bearing their OH substituents and a proper functionality for the generation of the two C-C or the two C-heteroatom bonds involved in the generation of the carbo- or heterocyclic ring. Two approaches have been developed for these purposes.

Sugar triflates showed to be more suitable for these purposes, due to their easy preparation and their high reactivity, that facilitates the easy and efficient formation of the new ring by intramolecular nucleophilic displacements both prior or after the opening of the sugar ring. The alternative of using sugar dimesylates or sugar ditriflates for the simultaneous formation of the two key bonds leading to the new ring is particularly attractive, but has some limitations. In fact, for the formation of ditriflates from diols, it is necessary the absence of a neighboring hydroxyl group that could lead to intramolecular cyclization, particularly to a five membered ring.

The synthesis of carbocycles and heterocycles from sugar ditriflates is at present practically limited to several synthesis of azetidines. This article reports further chemistry on in this field. It includes new divergent synthesis of iminocyclopentitols anad 3,4-dihydroxyprolines