Kinetic studies on the rearrangement of 3,4-di-O-benzyl-1,2-O-(1-methoxyethylidene)-β-l-rhamnopyranose with a catalytic amount of 1,1,3,3-tetramethylurea-trifluoromethanesulfonic acid at different temperatures

Banoub, Joseph; Michon, Francis; Rice, Jake; Rateb, Latif

doi:10.1016/0008-6215(83)88385-2

Cited by 6 publications

(2 citation statements)

References 7 publications

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“…On this basis, it was suggested that the rearrangement follows an intramolecular path via a contact ion pair in which the migrating alcohol remains in close contact with the dioxalenium ion before ultimate recombination with ring opening to give the glycoside (Scheme 3). 121 DFT computational work by Whitfield and coworkers on the rearrangement of a methyl orthoester in the 6-Oacetyl-3,4-O-isopropylidene-D-galactopyranose series using continuum dielectric model for solvation arrived at an analogous conclusion, albeit no counterion was included in the computation. 108 The alternative mechanism is one involving complete dissociation of the alcohol, or its complex with the activating Lewis acid, from the dioxalenium ion prior to recombination with ring opening and glycosidic bond formation.…”

Section: Orthoesters As Intermediates In Glycosylation Reactions Dire...mentioning

confidence: 99%

Mechanisms of Stereodirecting Participation and Ester Migration from Near and Far in Glycosylation and Related Reactions

et al. 2020

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This review is the counterpart of a 2018 Chemical Reviews article that examined the mechanisms of chemical glycosylation in the absence of stereodirecting participation. Attention is now turned to a critical review of the evidence in support of stereodirecting participation in glycosylation reactions by esters from either the vicinal or more remote positions. As participation by esters is often accompanied by ester migration, the mechanism(s) of migration are also reviewed. Esters are central to the entire review, which accordingly opens with an overview of their structure and their influence on the conformations of six-membered rings. Next the structure and relative energetics of dioxacarbeniun ions are covered with emphasis on the influence of ring size. The existing kinetic evidence for participation is then presented followed an overview of the various intermediates either isolated or characterized spectroscopically. The evidence supporting participation from remote or distal positions is critically examined and alternative hypotheses for the stereodirecting effect of such esters is presented. The mechanisms of ester migration are first examined from the perspective of glycosylation reactions, and then more broadly in the context of partially acylated polyols.

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Section: Orthoesters As Intermediates In Glycosylation Reactions Dire...mentioning

confidence: 99%

Mechanisms of Stereodirecting Participation and Ester Migration from Near and Far in Glycosylation and Related Reactions

et al. 2020

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“…The main debate therefore revolves around the mechanism of the acid-catalyzed rearrangement of the orthoester to the glycoside, a subject, which has been the focus of surprisingly little experimental work. Banoub and coworkers determined the rearrangement of a rhamnopyranosyl orthoester to the corresponding a-rhamnoside to follow first-order kinetics on catalysis with triflic acid in the presence of tetramethylurea and, on the basis of the large negative value of the free entropy of activation, concluded that the mechanism was intramolecular and involves a tight ion pair intermediate [112]. Somewhat remarkably in view of the extremely widespread use of neighboring group directed glycosylation, crossover experiments were not reported in the literature until 2000.…”

Section: Intramolecular Participation Protecting Groupsmentioning

confidence: 99%

A propos of glycosyl cations and the mechanism of chemical glycosylation

Bohé¹,

Crich²

2010

Comptes Rendus. Chimie

109

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Glycosylation with Sulfoxides and Sulfinates as Donors or Promoters

Crich

Lim

2004

Organic Reactions

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The efficient, stereocontrolled formation of glycosidic bonds is arguably the most fundamental reaction in glycoscience. This chapter surveys four recent distinct glycosylation methods united by the common theme of employing sulfoxides, or closely related sulfinates, either in the glycosyl donor itself or as an integral part of the promoter. In the first method (the sulfoxide method), a glycosyl sulfoxide, the donor, is coupled to an acceptor alcohol by means of an activating agent to give the glycosidic bond. The activating agent is typically triflic anhydride, but other compounds have been used. In the second method (the thiogylcoside method) the donor is thioglycoside. It is activated by means of a promoter derived from the reaction of trifluoromethanesulfonic anhydride and thiosulfinate, a sulfinaminde, or diphenylsulfoxide before coupling to an acceptor alcohol. The third method is dehydrative coupling. This chapter is concerned only with the recent variations in which dehydration is achieved by means of a combination of diaryl sulfoxides and trifluoromethanesulfonic acid. The last method (the oxidative method), involves the direct oxidative glycosylation of glycals. This method differs significantly from the other methods since it does not employ a traditional anomeric derivative as glycosly donor, but derives one from the formal oxidation of glycal. At some time in the activation process, all four methods typically involve the reaction of a sulfoxide, or sulfinate with trifluoromethanesulfonic anhydride. All four methods possess the distinct advantage of using readily prepared, stable gylcosyl donors. Three of them are metal‐free and two of them are capable of coupling to enable the most hindered unreactive alcohols in a matter of minutes at low temperature. These methods are some of the most powerful available for the formation of glycosidic linkages.

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Kinetic studies on the rearrangement of 3,4-di-O-benzyl-1,2-O-(1-methoxyethylidene)-β-l-rhamnopyranose with a catalytic amount of 1,1,3,3-tetramethylurea-trifluoromethanesulfonic acid at different temperatures

Cited by 6 publications

References 7 publications

Mechanisms of Stereodirecting Participation and Ester Migration from Near and Far in Glycosylation and Related Reactions

Mechanisms of Stereodirecting Participation and Ester Migration from Near and Far in Glycosylation and Related Reactions

A propos of glycosyl cations and the mechanism of chemical glycosylation

Glycosylation with Sulfoxides and Sulfinates as Donors or Promoters

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