Intramolecular 1,5-Hydrogen Atom Transfer Reactions under reductive conditions in Monosaccharide Systems

Abstract

L‐Sugars play important roles because they are constituents of antibiotics and clinically functional nucleosides. However, besides their usefulness, L‐sugars are rare in nature and in consequence, expensive. Thus, it becomes necessary to develop efficient methods for their synthesis and some synthetic routes have been reported a few years ago. Recently in our group, the intramolecular 1,8‐hydrogen atom transfer (1,8‐HAT) reaction under reductive conditions has been studied in disaccharide derivatives observing that in well‐disposed substrates, an inversion at C‐5’ takes place with excellent diastereoselectivity, as it ocurrs in β‐maltose. Considering these previous results, herein, the 1,5‐HAT reaction under reductive conditions in monosaccharide systems is described, studying the stereoselective reduction of the C‐4 and C‐5 radical intermediates in furanoses and pyranoses, respectively. As observed in previous work, the reaction strongly depends on steric and stereoelectronic effects of the substituents in the carbohydrate ring. A proper choice of the configuration and the electronic nature of these substituents could be very efficient in our task to generate inversion of the configuration at C‐4 or C‐5.