β-Fragmentation of primary alkoxyl radicals versus hydrogen abstraction: synthesis of polyols and α,ω-differently substituted cyclic ethers from carbohydrates

Abstract

The β-fragmentation of primary alkoxyl radicals, described in many cases as low-yielding and plagued by side reactions, can proceed in satisfactory yields using carbohydrate substrates. The only reaction that can compete significantly with the β-scission is the intramolecular hydrogen abstraction. The ratio of β-fragmentation to hydrogen abstraction can be varied according to the reaction conditions, the stereochemistry of the substituents (e.g., α- or β-anomeric substituents), and the protecting groups chosen. The carbohydrate substrates are easily prepared, and the mild reaction conditions are compatible with most functional groups. The β-scission reaction provides an expedient way toward shorter and less common sugar series and also toward α,ω-differently substituted cyclic ethers. These units are useful building blocks and are present in many natural products with interesting biological activity.