Sulfonium Ions as Reactive Glycosylation Intermediates

Nokami, Toshiki

doi:10.4052/tigg.24.203

Cited by 17 publications

(13 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Many other additives have been investigated, − and an increasing number have been spectroscopically and in rare cases even crystallographically characterized. The most promising in recent years appears to be a series of tertiary formamides, with DMF as the prototypical example and varying in size and electronic character of the N -substituents. , The use of amides in this manner results in the formation of a pair of glycosyl imidates, with the axial isomer being the more stable and the equatorial one the more reactive, leading overall to preferential formation of the axial glycoside provided the conditions are such as to promote rapid equilibration of the two imidates .…”

Section: Resultsmentioning

confidence: 99%

Guidelines for O-Glycoside Formation from First Principles

Andreana

Crich

2021

ACS Cent. Sci.

View full text Add to dashboard Cite

show abstract

Section: Resultsmentioning

confidence: 99%

Guidelines for O-Glycoside Formation from First Principles

Andreana

Crich

2021

ACS Cent. Sci.

View full text Add to dashboard Cite

show abstract

“…The influence of additives such as tetraalkylammonium bromides 4,62 and tetramethylurea 63 on glycosylation reactions has been studied for many years with covalent intermediates isolated and well-characterized in some cases. 64 Recent examples on the study of additives include the addition of sulfides and sulfoxides, which afford stable glycosyl sulfonium and oxysulfonium salts, 30,65–66 and of dimethylformamide and other secondary amides, and even catalytic oxindoles, 67 leading to the formation of glycosyl imidates. 68–69 The additives area has been reviewed recently and as such we will not comment further on it here, 70 but rather we will limit ourselves to counter ions.…”

Section: Counterion and Additive Effectsmentioning

confidence: 99%

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

Bohé

Crich

2015

Carbohydrate Research

125

View full text Add to dashboard Cite

An overview of recent advances in glycosylation with particular emphasis on mechanism is presented. The mounting evidence for both the existence of glycosyl oxocarbenium ions as fleeting intermediates in some reactions, and the crucial role of the associated in counter ion in others is discussed. The extremes of the SN1 and SN2 manifolds for the glycosylation reaction are bridged by a continuum of mechanisms in which it appears likely that most examples are located.

show abstract

“…4 This type of compound was first described by Schuerch and co-workers who treated a per- O -benzylated glucosyl bromide with dimethyl sulfide to give acyclic β -dimethyl-sulfonium ion. 5 Addition of methanol to the in situ formed sulfoniun ion led to the formation of the corresponding methyl glycoside as predominantly the α -anomer.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Glycosylation of Anomeric Sulfonium Ions

Fang

Huang

et al. 2016

J. Am. Chem. Soc.

View full text Add to dashboard Cite

Anomeric sulfonium ions are attractive glycosyl donors for the stereoselective installation of 1,2-cis glycosides. Although these donors are receiving increasing attention, their mechanism of glycosylation remains controversial. We have investigated the reaction mechanism of glycosylation of a donor modified at C-2 with a (1S)-phenyl-2-(phenylsulfanyl)ethyl chiral auxiliary. Preactivation of this donor results in the formation of a bicyclic β-sulfonium ion that after addition of an alcohol undergoes 1,2-cis-glycosylation. To probe the importance of the thiophenyl moiety, analogs were prepared in which this moiety was replaced by an anisoyl or benzyl moiety. Furthermore, the auxiliaries were installed as S- and R-stereoisomers. It was found that the nature of the heteroatom and chirality of the auxiliary greatly influenced the anomeric outcome and only the one containing a thiophenyl moiety and having S-configuration gave consistently α-anomeric products. The sulfonium ions are sufficiently stable at a temperature at which glycosylations proceed indicating that they are viable glycosylation agents. Time-course NMR experiments with the latter donor showed that the initial rates of glycosylations increase with increases in acceptor concentration and the rate curves could be fitted to a second order rate equation. Collectively, these observations support a mechanism by which a sulfonium ion intermediate is formed as a trans-decalin ring system that can undergo glycosylation through a bimolecular mechanism. DFT calculations have provided further insight into the reaction path of glycosylation and indicate that initially a hydrogen-bonded complex is formed between sulfonium ion and acceptor that undergoes SN2-like glycosylation to give an α-anomeric product.

show abstract

Sulfonium Ions as Reactive Glycosylation Intermediates

Cited by 17 publications

References 30 publications

Guidelines for O-Glycoside Formation from First Principles

Guidelines for O-Glycoside Formation from First Principles

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

Mechanism of Glycosylation of Anomeric Sulfonium Ions

Contact Info

Product

Resources

About