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UV light-promoted reduction of acetobromoglucose by NaBH3CN in t-BuOH afforded 1,3,4,6-tetra-O-acetyl-2-deoxy-α- d -arabino-hexopyranose in high yield and purity, via a Surzur–Tanner rearrangement, while, with 10 mol % thiophenol added, acetylated 1,5-anhydro- d -glucitol was cleanly obtained. Such tin-free and mild reductions, presumed to proceed via radical pathways, were more efficient with NaBH3CN compared to NaBH4 or NaBD4, and do not occur with acetochloroglucose. Similar reductions to 1,3,4,6-tetra-O-acetyl-2-deoxy-α- d -arabino-hexopyranose were achieved upon heating to 80 °C t-BuOH or CH3CN solutions of NaBH3CN and AIBN, but with a lower selectivity due to competing ionic reactions. With other pyranosyl bromides, reductions by NaBH3CN could be tuned similarly ( d -galacto), but some ( d -manno, 5-thio- d -xylo) gave mainly or exclusively 1,5-anhydro-itols. Other conditions, or reagents promoting SET process, afforded also reduced products, but with lower rates or selectivities. Primary iodides were reduced readily with NaBH3CN under UV light.

Glycoligands, which feature a glycoside as the central template incorporating Lewis bases as metal chelation sites and various fluorophores as the chemical reporter, represent a range of interesting scaffolds for development of chemosensors. Here, new types of triazolyl bidentate glycoligands (TBGs) based on the grafting of 3-azidocoumarin to the C2,3- or C4,6-positions of three epimeric pyranoglycosides including a glucoside, a galactoside, and a mannoside were efficiently synthesized via a fluorogenic dual click reaction assisted by microwave irradiation. The desired TBGs were afforded in high conversion rates (>90%) and reasonable yields (∼70%). Moreover, a preliminary optical study of two hydroxyl-free glucoside-based TBGs indicates that these compounds are strongly fluorescent in pure water, implying their potential for ion detections in aqueous media.

International audience; Glycosidation of sugar peracetates (D-gluco, D-galacto) with SnCl(4) and CF(3)CO(2)Ag led to either 1,2-cis-, or 1,2-trans-glycosides, depending primarily on the alcohols used. In particular, 1,2-trans-glycosides, expected from acyl-protected glycosyl donors, were formed in high yields with alcohols sharing specific features such as bulkiness, presence of electron-withdrawing groups or polyethoxy motifs. In contrast, simple alcohols afforded approximately 1:1 mixtures of 2,3,4,6-tetra-O-acetyl, and 3,4,6-tri-O-acetyl 1,2-cis-glycosides due to anomerization and/or acid-catalyzed fragmentation of 1,2-orthoester intermediates. After reacetylation or deacetylation, acetylated or fully deprotected 1,2-cis-glycosides (alpha-D-gluco, alpha-D-galacto) were obtained in approximately 90% yields by a simple and direct method.

Never-theless, although these glycosylations proceeded smoothly and afforded effectively the final product, there still remain several drawbacks such as incomplete anomeric retention, relatively low total yield and especially, long reaction time (commonly more than 24 h for 2 - 3 steps).Microwave irradiation is known as a powerful tool for both enhancing the reaction efficacy and economizing the reaction time. To our surprise, though this methodology has been ma-ssively introduced into carbohydrate chemistry