Direct C-Glycosylation by Indium-Mediated Alkynylation on Sugar Anomeric Position

Abstract

Indium-mediated alkynylation reaction was studied for the direct preparation of C-glycosides. Easily available starting sugar derivatives with an acetyl group at the anomeric position were tested as electrophiles toward alkynylindium reagents under Barbier conditions. Good yields and stereoselectivities were observed during the reaction. The alkynylation was applied to the synthesis of an alpha-(1-->6)-C-disaccharide analogue of isomaltoside.

Synthesis of ribavirin 2’-Me-C-nucleoside analogues

“…Debenzoylation of 4 followed by selective protection led to derivative 5 , which was submitted to the indium-mediated alkynylation reaction affording the alkynyl riboside 6 with the same β-anomeric selectivity as for the non-methylated derivative [21]. Then, the 1,3-dipolar cycloaddition reaction of 6 with benzyl azide in toluene at 70 °C led to a mixture of regioisomeric triazoles 7 in a 42:58 ratio.…”

The synthesis of d-C-mannopyranosides

“…Indium-mediated alkynylation has also been reported starting from the protected mannose derivative 4 (Scheme 12) [110]. The a-anomer was obtained in good yield as the major reaction product.…”

Iron(III) chloride catalyzed glycosylation of peracylated sugars with allyl/alkynyl alcohols

“…Due to the importance of glycosylic compounds, the present subject has received considerable attention in recent years. 3 Substantial number of reports has appeared in the literature on glycosylation reaction employing common reagents such as BF 3 .OEt 2 , 4 indium metal, 5 HClO 4 -SiO 2 , 6 InCl 3 /IBX (iodoxybenzoic acid), 7 InBr 3 8 and SnCl 4 . 9 Glycosides have been also synthesized via Ferrier rearrangement starting from the corresponding unsaturated glycosides with alcohols in presence of InCl 3 , 10 Bi(OTf) 3 /SiO 2 -Bi(OTf) 3 11 and other acid catalysts.…”

“…15 In addition, iron chloride was successfully employed for the Ferrier rearrangement. 16 Whilst there are several published procedures [4][5][6][7][8][9][10][11][12] for the glycosylation reactions, many of these methods require the use of expensive reagents and have limitations in terms of yields, stereoselectivities, reaction temperature, the catalyst/reagents used and their quantitative amounts. Therefore, our aim was to find a method that utilized mild, relatively cheap reagents and flexible enough to allow the synthesis of glycosides.…”