C-Glycosides Synthesis

The bulk of the techniques make use of the glycosidic C—C bond. These C-glycosylation techniques are grouped here according to the readily available, often used glycosyl donor precursors for O-glycoside production. They consist of glycosyl halides, glycals, sugar acetates, sugar lactols, sugar lactones, 1,2-anhydro sugars, thioglycosides/sulfoxides/sulfones, selenoglycosides/telluroglycosides, methyl glycosides, and glycosyl imidates/phosphates. Under each category of sugar precursor, glycosyl electrophilic/cationic species, anionic species, radical species, or transition-metal complexes are described as potential mechanisms for C-glycosylation processes. Another group of C-glycosylations is intramolecular rearrangements, which often include coordinated processes and include the Claisen, Ramberg-Bäcklund, and 1,2-Wittig rearrangements. The development of pyranoside/furanoside rings after the building of the predetermined glycosidic C—C bonds, which might involve cyclization of acyclic precursors or D–A cycloadditions.