Synthesis of 2,3-unsaturated thioglycopyranosides mediated by lithium tetrafluoroborate
TL;DR: In this paper, tri-O acetyl-D-glucal 1 with diverse thiols was treated in the presence of LiBF4 in CH3CN, furnished aryl/alkyl 2,3-unsaturated thioglycopyranosides 8−13 (56-72%).
About: This article is published in Tetrahedron Letters.The article was published on 1999-07-30. It has received 21 citations till now. The article focuses on the topics: Lithium tetrafluoroborate & Ferrier rearrangement.
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TL;DR: A review of recent developments in the use of promoters for the Ferrier rearrangement of O-, N-, C- and S-nucleophiles with glycals can be found in this paper.
121 citations
TL;DR: Er(OTf)(3) is a useful catalyst for the Ferrier rearrangement furnishing high yields of O- and S-glycosides and the catalyst, which is also commercially available, can be recovered and reused.
44 citations
TL;DR: In this paper, the reaction of tri-O-acetyl-D-glucal with different nitrogen nucleophiles was effectively promoted by a catalytic amount of tris(pentafluorophenyl)borane for the first time in acetonitrile at room temperature to produce a variety of azapseudoglycals via Ferrier rearrangement.
43 citations
TL;DR: In this paper, the utility of the Ferrier reaction to access S-linked disaccharides and Slinked glycoamino acids has been probed, and access to a range of 1,4 and 1,6-S-linked derivatives has been achieved using glycals derived from glucose and galactose, and sulfur containing coupling partners derived from methyl α-d-glucopyranoside.
37 citations
TL;DR: In this paper, the Ferrier glucosylation of alcohols with 3,4,6-tri- O-acetyl-d-glucal has been investigated with several metal nitrates and the optimal catalyst is bismuth nitrate pentahydrate (BNP).
Abstract: The Ferrier glucosylation of alcohols with 3,4,6-tri- O-acetyl-d-glucal has been investigated with several metal nitrates and the optimal catalyst is bismuth nitrate pentahydrate (BNP). Good yields of pseudoglycals were also obtained with ferric nitrate nonahydrate (FNN), heightening the catalyst dosage (50 mol%) being required however. The BNP-mediated reactions showed remarkable solvent dependency and in the optimal protocol, the amount of BNP as low as 10 mol% was effective, furnishing excellent yields of O-glucosides with good anomeric selectivity in acetonitrile. A comparison of BNP and FNN in terms of yields and selectivity of the product has been made. In comparison to the reactions in acetonitrile, the catalytic ability of BNP was found to enhance drastically in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF 6]. © 2005 Elsevier B.V. All rights reserved.
37 citations
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TL;DR: A review of the use of thioglycosides as glycosyl donors in oligosaccharide synthesis is given in this article, where both indirect and direct use, by electrophilic activation of the thi glycoside, are discussed.
Abstract: A review is given of the use of thioglycosides as glycosyl donors in oligosaccharide synthesis Both indirect use, by conversion of the thioglycoside into a glycosyl halide and direct use, by electrophilic activation of the thioglycoside, are discussed
229 citations
TL;DR: Schmidt et al. as discussed by the authors proposed the use of tris(4-bromophenyl)aniumyl hexachloroantimonate, a one-electron transfer homogeneous reagent, which nicely activates in acetonitrile various ethyl or phenyl S-glycosides having either participating or non-participating substituents at C-2 to give p-0-sides in good yield.
Abstract: Several novel solutions to the efficient and selective preparation of glycosides are presented. Commercial tris(4-bromophenyl)aniumyl hexachloroantimonate, a one-electron transfer homogeneous reagent, nicely activates in acetonitrile various ethyl or phenyl S-glycosides having either participating or non-participating substituents at C-2 to give p-0-glycosides in good yield. In a variation on the theme, phenyl S-glycosides react with alcohols under mild electrochemical conditions to give the corresponding 0-glycosides. Azidoxanthates, prepared via a two-step sequence from various galactals, are efficient galactosyl donors for the steroselective synthesis of protected precursors of biologically important galactosamine-containing oligosaccharides. We have also discovered that anomeric enol-ethers, or the corresponding carbonates, are remarkably efficient glycosyl donors. Finally, a "non-orthodox" strategy based on the idocyclization of appropriate acyclic enol-ethers resulted in a novel approach to KDO-containing disaccharides. This last synthesis critically benefited from the use of the Tebbe reagent for the preparation of the key starting enol ethers. INTRODUCTION Simple, efficient and selective preparation of oligosaccharides is a central problem in carbohydrate chemistry. The historical publication of Koenigs and Knorr, in 1901, first introduced glycosyl halides as glycosyl donors (ref.l), and launched a method which -through a vast series of variations -has been by and large the essential one for a very long period of time (ref. 2, 3). The introduction of the orthoester procedure was probably the first important attempt to find an alternative to the Koenigs-Knorr method (ref. 4). This reaction has been refined over the years, mainly by the Russian School (ref. 5, 6). A subtle understanding of the chemical properties of the halogeno sugars resulted in 1975 in the development by Lemieux et aZ.(ref. 7, 8) of the halide-catalyzed glycosylation reaction which has been successfully applied to the synthesis of several blood group antigenic determinants. A limitation of this variation on the theme was the lack of reactivity with many "sugar alcohols" with weak reacting capacities, typically methyl 2,3,6-tri-0-benzyl-a-~-glucopyranoside (r f. 9) which has become, over recent years, a standard for evaluating the "road holding" of any novel glycosylation strategy. In 1978 we disclosed the imidate procedure (ref. lo), a novel alternative to the Koenigs-Knorr reaction. The disadvantage of our original procedure -a rather laborious synthesis of the glycosyl donor from a halogeno sugar -was circumvented by R. R. Schmidt et al. (ref. 11) and the imidate glycosylation reaction is now of much more use in the field. It is important to stress that the much higher reactivity of trichloroacetimidates compared to acetimidates may be detrimental to the a-selectivity. Indeed, the mild acetimidate glycosylation reaction is highly selective, a distinct advantage which should be kept in mind when dealing with sufficiently reactive acceptors. This research has probably contributed to moving further and further away from the time-resistant "paradigm" introduced by Koenigs and Knorr at the turn of the century. With the availability of efficient glycosyl donors paving at last the avenue to higher oligosaccharides of biological relevance, a practical difficulty soon emerged: in order to keep manipulation of complex oligosaccharide fragments to a minimum, and to fully explicit convenient synthesis, it appeared important to build blocks which could be directly transferred to an acceptor upon activation. Thioglycosides are now attracting considerable attention in this respect (ref. 12). They are stable under a variety of chemical transformations and can be activated by thiophilic reagents. Recent results obtained in the author's laboratory in the field of glycosylation are now being analyzed in this lecture which can be divided into four main topics. 1) Activation of thioglycosides with either TBPA+', a one-electron transfer homogeneous reagent, or via anodic oxidation (heterogeneous one-electron transfer). 2) Use of anomeric S-xanthates of 2-azido-2-deoxy-D-galactopyranosyl derivatives as efficient glycosyl donors. 3) Synthesis and use of anomeric enol-ethers, or the corresponding carbonates, as novel glycosyl donors. 4) Development of "non-orthodox" strategies for the synthesis of KDOcontaining disaccharides. 519
169 citations
TL;DR: In this paper, the authors describe the Hydrolysis of Acetals and Ketals using LiBF4 and show that it is possible to synthesize acetal and ketal using only LiBF 4.
119 citations
TL;DR: In this article, a β-trimethylsilylethyl glycoside was used to protect the anomeric center in various carbohydrates. But the free sugar can be regenerated using LiBF 4 in acetonitrile.
75 citations