Study On The Synthesis Of C-Glycosides Using Metal/Photoredox Reactions

C-glycosides are one class of biologically stable carbohydrates,which have been widely used in the fields of biochemistry and pharmaceuticals.C-glycosylation via anomeric glycosyl radical intermediates is a particularly attractive approach for the synthesis of C-glycosides,owing to mild reaction conditions and great compatibility with various functionality;In this thesis,we describe our effort in the synthesis of Cglycosides through metallphotoredox reactions(or photoredox reactions),which can be divided into the following two parts:Part 1: We have realized the cross-coupling reaction of uronic acids with aryl halides or alkynes in the presence of metallphotoredox catalysis.Ribofuranuronic acids can smoothly react with various aryl halides or alkynes to form the target C-glycosides,whereas pyranuronic acids cannot deliver the desired products,but rather give byproducts resulted from esterification and homo-coupling.Part 2: On the basis of the above work,we have successfully achieved the homocoupling reaction of uronic acids mediated by visible light.This reaction can be used to construct natural products with multiple consecutive hydroxyl groups.The stereoselectivity can be explained by the stereoelectronic effect of the preferred conformation of the glycosyl radical intermediates.The above work has laid a solid foundation for the research group in the development of more efficient C-glycosylation reactions.