HClO4–SiO2 catalyzed per-O-acetylation of carbohydrates

Ionic Liquid Catalyzed Per-O-Acetylation and Benzylidene Ring-Opening Reaction

Tunable aryl imidazolium ionic liquids acting as Brønsted acid ionic liquids were found to be efficient catalysts for per-O-acetylation and reductive ring opening of benzylidene acetals. This method requires a truly catalytic amount of the least expensive available ionic liquids that are water-stable and reusable and also stable at room temperature. The reactions were obtained in one hour with good to excellent yields. These reactions can form C−O and C−H bonds with a high atom economy. Furthermore, the ionic liquid is an anomeric selective catalyst in per-O-acetylation and reductive ring opening of benzylidene acetals of sugar moieties.

Selective acetolysis of primary benzyl groups in carbohydrate derivatives under the mild reaction condition

Selective acetolysis of the primary benzyloxy groups in a wide variety of carbohydrate derivatives was achieved in excellent yield using acetic anhydride and perchloric acid supported over silica (HClO₄-SiO₂) as a solid acid catalyst in a fast reaction condition without using any organic solvent. The reaction condition is significantly rapid and can be scaled up for its use in the multi-step oligosaccharide synthesis.

Helicity control of π-conjugated foldamers containing d-glucose-based single enantiomeric units as a chiral source

We have succeeded in the helicity control of polymer backbones and their circularly polarized luminescence without the need for chirality of an unnatural antipode, l-glucose.

Efficient one-pot per-O-acetylation–thioglycosidation of native sugars, 4,6-O-arylidenation and one-pot 4,6-O-benzylidenation–acetylation of S-/O-glycosides catalyzed by Mg(OTf)2

Sequential one-pot per-O-acetylation–S-/O-glycosidation under neat condition, regioselective 4,6-O-arylidenation and sequential one-pot benzylidenation–acetylation of Mg(OTf)₂as non-hygroscopic, recyclable catalyst are reported.

An extremely efficient and green method for the acylation of secondary alcohols, phenols and naphthols with a deep eutectic solvent as the catalyst

An efficient and green method was developed for the acylation of secondary alcohols, phenols and naphthols using deep eutectic solvent [CholineCl][ZnCl₂]₃ as a catalyst at room temperature under solvent-free conditions.

Acyl transfer reactions of carbohydrates, alcohols, phenols, thiols and thiophenols under green reaction conditions

Acyl transfer reactions of various carbohydrates, alcohols, phenols, thiols and thiophenols were achieved at room temperature in high yields and catalytic efficiency in the presence of methane sulfonic acid, a green organic acid, under solvent-free conditions over short time periods.

Cu(ClO4)2·6H2O catalyzed solvent free per-O-acetylation and sequential one-pot conversions of sugars to thioglycosides

The solvent free per-O-acetylation of various reducing and non-reducing sugars has been carried out using stoichiometric amounts of acetic anhydride and copper(ii) perchlorate hexahydrate as the catalyst.

Zeolites and other silicon-based promoters in carbohydrate chemistry

Silicon-based materials, namely zeolites, clays, and silica gel have been widely used in organic synthesis, allowing mild reaction conditions and environmentally friendly methodologies. These heterogeneous catalysts are easy to handle, possess nontoxic and noncorrosive character and offer the possibility of recovery and reuse, thus contributing to clean and sustainable organic transformations. Moreover, they present shape-selective properties and provide stereo- and regiocontrol in chemical reactions. Herein, we survey the most significant applications of silicon-based materials as catalysts in carbohydrate chemistry, to mediate important transformations such as glycosylation, sugar protection and deprotection, and hydrolysis and dehydration. Emphasis is placed on their promising synthetic potential in comparison with conventional catalysts.

Activation of glycosyl trichloroacetimidates with perchloric acid on silica (HClO(4)-SiO(2)) provides enhanced alpha-selectivity

Obtaining high stereoselectivity in glycosylation reactions is often challenging in the absence of neighboring group participation. In this study, we demonstrate that activation of glycosyl trichloroacetimidate donors with immobilized perchloric acid on silica (HClO(4)-SiO(2)) provides higher alpha-selectivity than trimethylsilyl triflate (TMSOTf) for reactions that do not involve neighboring group participation.

Indium triflate catalyzed peracetylation of carbohydrates

Peracetylation is a very common protection strategy that is widely implemented in carbohydrate synthesis. Here, a method for the peracetylation of carbohydrates using catalytic In(OTf)(3) in neat acetic anhydride is reported. In(OTf)(3) has low toxicity and is mild and water tolerant, and the reactions are high yielding and efficient. Details regarding the scope and mechanism of the reaction are briefly discussed.

Synthesis of a di- and a trisaccharide related to the O-antigen of Escherichia coli O83:K24:H31

Di- and trisaccharide fragments related to the repeating unit of the O-antigen of Escherichia coli O83:K24:H31 have been synthesized as their methyl glycoside analogs starting from readily available monosaccharides.

Acylation of carbohydrates over Al2O3: preparation of partially and fully acylated carbohydrate derivatives and acetylated glycosyl chlorides

Selective and per-O-acylation of carbohydrate derivatives using acyl chlorides and Al2O3, a solid support reagent, is reported. This protocol does not require the addition of any base or activator. This methodology has been further extended to the selective acylation of carbohydrate diols and the one-pot preparation of acetylated glycosyl chlorides direct from free reducing sugars. The yields obtained in most of the cases are excellent.

From Solution Phase to “On-Column” Chemistry: Trichloroacetimidate-Based Glycosylation Promoted by Perchloric Acid−Silica

[reaction: see text] Activation of ester-protected glycosyl trichloroacetimidate donors by perchloric acid immobilized on silica afforded 1,2-trans disaccharides in 60-90% yields. Applying this approach to one-pot sequential glycosylation resulted in efficient syntheses of the N-linked glycan trimannoside and Le(X) and Le(A) trisaccharides in very good yield (76%, 62%, and 59% yields, respectively). Solution phase reactions were also translated to a solid phase format; priming the top of a standard silica chromatography column with perchloric acid immobilized on silica facilitated "on-column" glycosylation with subsequent "in situ" purification of products. Coupling yields from this approach were comparable to those obtained from the corresponding solution-phase disaccharide couplings. A series of glycosylated amino acids were also synthesized in high yield with use of the on-column approach.

One-pot acetalation–acetylation of sugar derivatives employing perchloric acid immobilised on silica

Perchloric acid immobilised on silica gel has been used as an efficient promoter for per-O-acetylation, and acetalation and subsequent O-acetylation of glycosides and thioglycosides in one-pot using stoichiometric reagents.