β-Glycosyl Trifluoroborates as Precursors for Direct α-C-Glycosylation: Synthesis of 2-Deoxy-α-C-glycosides

Abstract

C-Glycosides are metabolically stable mimics of natural O-glycosides and are expected to be useful tools for investigation of the biological functions of glycans. Here, we describe the synthesis of a series of aryl and vinyl C-glycosides by stereoinvertive sp3–sp2 cross-coupling reactions of 2-deoxyglycosyl boronic acid derivatives with aryl or vinyl halide, mediated by a photoredox/nickel dual catalytic system. Hydrogenation of the vinyl C-glycosides afforded C-linked 2′-deoxydisaccharide analogues.

Synthesis of C-acyl furanosides via the cross-coupling of glycosyl esters with carboxylic acids

“…Pyranosyl radicals have been generated from various unnatural glycosyl derivatives, including bromides, 18 xanthates, 19 glycals, 20 stannanes, 21 thiol ethers, 22 acyl tellurides, 23 and trifluoroborates. 24 Precursors to furanosyl radicals, however, are limited to unnatural tetrahydrofuran derivatives with a carboxylic acid at the C1 position, restricting the scope of carbohydrate substrates. 25 Furthermore, redox auxiliaries based on C–C bond homolysis can only substitute at the C5 of furanosides and the C6 of pyranosides, not allowing for anomeric functionalization.…”

Light-Mediated Cross-Coupling of Anomeric Trifluoroborates

“…17c, 18 Based on this literature precedent, we further hypothesized that with a proper control of the electronic effects either through the modulation of the protective groups or ligands on the highvalent nickel center, axial trifluoroborates could effectively undergo a stereoretentive coupling with electrophilic partners. This proposal was supported by a recent study from the Hirai group 19 featuring the synthesis of stable siliconprotected potassium trifluoroborates of 2-deoxy--D-glucose and β-D-galactose. Here, we report the synthesis and stereoretentive C-C cross-coupling reactions of α-anomeric trifluoroborates 9 of common mono-and disaccharides under the photoredox conditions (Scheme 1C).…”

Light-Mediated Cross-Coupling of Anomeric Trifluoroborates

“…These reagents have been shown to partake in light-mediated reactions with aryl halides using nickel and photoredox catalysts engaged in a dual catalytic system. , On the basis of this literature precedent, we further hypothesized that with a proper control of the electronic effects either through the modulation of the protective groups or ligands on the high-valent nickel center, axial trifluoroborates could effectively undergo a stereoretentive coupling with electrophilic partners. This proposal was supported by a recent study from the Hirai group featuring the synthesis of stable silicon-protected potassium trifluoroborates of 2-deoxy-β- d -glucose and β- d -galactose. Here, we report the synthesis and stereoretentive C–C cross-coupling reactions of α-anomeric trifluoroborates 11 of common mono- and disaccharides under the photoredox conditions (Scheme C) .…”