Advances in the chemical synthesis of C-pyranosides/furanosides are summarized, covering the literature from 2000 to 2016. The majority of the methods take advantage of the construction of the glycosidic C—C bond. These C-glycosylation methods are categorized herein in terms of the glycosyl donor precursors, which are commonly used in O-glycoside synthesis and are easily accessible to nonspecialists. They include glycosyl halides, glycals, sugar acetates, sugar lactols, sugar lactones, 1,2-anhydro sugars, thioglycosides/sulfoxides/sulfones, selenoglycosides/telluroglycosides, methyl glycosides, and glycosyl imidates/phosphates. Mechanistically, C-glycosylation reactions can involve glycosyl electrophilic/cationic species, anionic species, radical species, or transition-metal complexes, which are discussed as subcategories under each type of sugar precursor. Moreover, intramolecular rearrangements, such as the Claisen rearrangement, Ramberg–Bäcklund rearrangement, and 1,2-Wittig rearrangement, which usually involve concerted pathways, constitute another category of C-glycosylations. An alternative to the C-glycosylations is the formation of pyranoside/furanoside rings after construction of the predetermined glycosidic C—C bonds, which might involve cyclization of acyclic precursors or D–A cycloadditions. Throughout, the stereoselectivity in the formation of the resultant C-glycosidic linkages is highlighted.

A practical and efficient synthesis of chloro(organophosphine) gold(I) complexes is reported. Employment of 4,4′-dihydroxydiphenyl sulfide as a safe and non-irritating reductant is highlighted for the generation of Au(I)–S intermediates, which could be trapped by mono- and bidentate phosphine ligands to provide organophosphine gold(I) complexes. The utility of the present method is further demonstrated by the synthesis of the antiarthritic drug auranofin.

•A rapid and efficient conversion of sialyl thioglycosides to sialyl esters was developed.•NIS/BF3OEt2-promoted glycosylation mainly provided β-sialyl esters within 5 min.•Complete β-selectivities were observed with the short-chain alkyl acids.A rapid and efficient one-step conversion of sialyl thioglycosides to sialyl esters was disclosed. Under the promotion of NIS and BF3OEt2, the glycosylation of per-acetylated sialyl thioglycoside with a set of carboxylic acids provided β-sialyl esters as the major products in good to excellent yields within 5 min. Compared with the long-chain alkyl-, aryl- and α,β-unsaturated acids, complete β-selectivities were observed when the short-chain alkyl acids were selected as the coupling partners. The resultant β-selectivity for the glycosylation of the per-acetylated sialyl thioglycoside with acetic acid was compromised when the 5-N,4-O-oxazolidinone protected sialyl thioglycoside was employed as the coupling partner.Download high-res image (89KB)Download full-size image

•A gold(I)-catalyzed glycosylation with Kdo ortho-hexynylbenzoate as donor is described.•The Kdo glycosides were obtained with excellent β-selectivities.•Synthesis of β-Kdo monosaccharide with a C5 linker at the reducing end is achieved.A gold(I)-catalyzed glycosylation of Kdo with glycosyl ortho-hexynylbenzoate as donor is reported. The couplings of Kdo ortho-hexynylbenzoate with a set of alcohols promoted by PPh3AuOTf afford Kdo glycosides with good β-selectivities. This glycosylation method allows for the synthesis of β-Kdo monosaccharide with a C5 linker at the reducing end for subsequent conjugation to carrier proteins and arrays.Download high-res image (127KB)Download full-size image