Is Donor−Acceptor Hydrogen Bonding Necessary for 4,6-O-Benzylidene-directed β-Mannopyranosylation? Stereoselective Synthesis of β-C-Mannopyranosides and α-C-Glucopyranosides

Crich, David; Sharma, Indrajeet

doi:10.1021/ol8017038

Cited by 45 publications

(47 citation statements)

References 31 publications

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“…This is because simple 4,6- O -benzylidene protected α- C -glucopyranosides, with an axial substituent at C1 but lacking the third ring, exist predominantly as 4 C 1 conformers (vide infra). 80–81 …”

Section: Resultsmentioning

confidence: 99%

Cation Clock Reactions for the Determination of Relative Reaction Kinetics in Glycosylation Reactions: Applications to Gluco- and Mannopyranosyl Sulfoxide and Trichloroacetimidate Type Donors

et al. 2015

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The development of a cation clock method based on the intramolecular Sakurai reaction for probing the concentration dependence of the nucleophile in glycosylation reactions is described. The method is developed for the sulfoxide and trichloroacetimidate glycosylation protocols. The method reveals that O-glycosylation reactions have stronger concentration dependencies than C-glycosylation reactions consistent with a more associative, SN2-like character. For the 4,6-O-benzylidene-directed mannosylation reaction a significant difference in concentration dependence is found for the formation of the β- and α-anomers suggesting a difference in mechanism and a rationale for the optimization of selectivity regardless of the type of donor employed. In the mannose series the cyclization reaction employed as clock results in the formation of cis and trans-fused oxabicyclo[4,4,0]decanes as products with the latter being strongly indicative of the involvement of a conformationally mobile transient glycosyl oxocarbenium ion. With identical protecting group arrays cyclization in the glucopyranose series is more rapid than in the mannopyranose manifold. The potential application of related clock reactions in other carbenium ion-based branches of organic synthesis is considered.

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Section: Resultsmentioning

confidence: 99%

Cation Clock Reactions for the Determination of Relative Reaction Kinetics in Glycosylation Reactions: Applications to Gluco- and Mannopyranosyl Sulfoxide and Trichloroacetimidate Type Donors

et al. 2015

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“…[13] Crich and Sharma have demonstrated that hydrogen bonding between glycosyl donors and acceptors is not an important factor in determining the stereoselectivity of glycosylation reactions. [36] Geometries were optimised using B3LYP/6-31G* [37] in Gaussian 03. [38] Additional single-point calculations using M06/6-31 + G** [39] were performed in Gaussian 09 [40] and gave results that correlated well with the original B3LYP/6-31G* calculations (see the Supporting Information).…”

Section: Wwwchemeurjorgmentioning

confidence: 99%

Do Glycosyl Sulfonium Ions Engage in Neighbouring‐Group Participation? A Study of Oxathiane Glycosyl Donors and the Basis for their Stereoselectivity

Fascione

Kilner

Leach

et al. 2011

Chemistry A European J

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Neighbouring-group participation has long been used to control the synthesis of 1,2-trans-glycosides. More recently there has been a growing interest in the development of similar strategies for the synthesis of 1,2-cis-glycosides, in particular the use of auxiliary groups that generate sulfonium ion intermediates. However, there has been some debate over the role of sulfonium ion intermediates in these reactions: do sulfonium ions actually engage in neighbouring-group participation, or are they a resting state of the system prior to reaction through an oxacarbenium ion intermediate? Herein, we describe the reactivities and stereoselectivities of a family of bicyclic thioglycosides in which an oxathiane ring is fused to the sugar to form a trans-decalin-like structure. A methyl sulfonium ion derived from one such glycosyl donor is so stable that it can be crystallised from ethanol, yet it reacts with complete stereoselectivity at high temperature. The importance of a ketal group in the oxathiane ring for maintaining this high stereoselectivity is investigated using a combination of experiment and ab initio calculations. The data are discussed in terms of S(N)1 and S(N)2 type mechanisms. Trends in stereoselectivity across a series of compounds are more consistent with selective addition to oxacarbenium ions rather than a shift between S(N)1 and S(N)2 mechanisms.

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“…Along with the previously described allylsilane additions, Crich and Sharma also reported the reaction of several different silyl enol ethers with thiomannoside 10 (Scheme 28) [134]. The b-C-mannosides were obtained with good overall selectivity and yield.…”

Section: [ ( S C H E M E _ 2 1 ) T D $ F I G ]mentioning

confidence: 89%

“…The authors noted that this selectivity was highly dependent on the presence of the benzylidene acetal and was also the result of tight ion pairs in the transition state, as in the case of the corresponding O-b-mannosides (Scheme 20) [134].…”

Section: [ ( S C H E M E _ 2 1 ) T D $ F I G ]mentioning

confidence: 99%

The synthesis of d-C-mannopyranosides

Choumane¹,

Banchet²,

Probst³

et al. 2010

Comptes Rendus. Chimie

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Is Donor−Acceptor Hydrogen Bonding Necessary for 4,6-O-Benzylidene-directed β-Mannopyranosylation? Stereoselective Synthesis of β-C-Mannopyranosides and α-C-Glucopyranosides

Cited by 45 publications

References 31 publications

Cation Clock Reactions for the Determination of Relative Reaction Kinetics in Glycosylation Reactions: Applications to Gluco- and Mannopyranosyl Sulfoxide and Trichloroacetimidate Type Donors

Cation Clock Reactions for the Determination of Relative Reaction Kinetics in Glycosylation Reactions: Applications to Gluco- and Mannopyranosyl Sulfoxide and Trichloroacetimidate Type Donors

Do Glycosyl Sulfonium Ions Engage in Neighbouring‐Group Participation? A Study of Oxathiane Glycosyl Donors and the Basis for their Stereoselectivity

The synthesis of d-C-mannopyranosides

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