Structures of Some Dialkoxyphenylmethylium Ions; Steric Inhibition of Resonance

Childs, Ronald F.; Frampton, Christopher S.; Kang, Guogong J.; Wark, Teresa A.

doi:10.1021/ja00098a010

Cited by 10 publications

(5 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition to the above groups of signals, all attributable to the base, its salts, and the benzoate groups, an intense new signal at δ 180.3 was observed. We assign this resonance to the cationic carbon in the bridging cation 17 , the chemical shift being fully consonant with the value of δ 182.9 found for C-2 in the authentic related dioxolenium ion 18 and with those of other related α,α-dialkoxybenzyl cations …”

Section: Resultssupporting

confidence: 79%

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: ¹³C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

1999

View full text Add to dashboard Cite

The role of ortho esters in the formation of 2,3,4-tri-O-benzoyl-β-xylopyranosides from various donor/promoter pairs has been investigated. It is concluded that for the activation of sulfoxides with Tf2O, thioglycosides with PhSOTf, and bromides with AgOTf the anomeric configuration of the donor is of no consequence on the outcome of the reaction. In all methods studied, the presence or absence of a non-nucleophilic, hindered base is of crucial importance with ortho esters only being discernible in its presence. S-Phenyl 2,3,4-tri-O-benzoyl-1-deoxy-1-thia-β-d-xylopyranoside was synthesized enriched with 13C at each of the three carbonyl carbons. Activation of this thioglycoside with PhSOTf in CD2Cl2 at −78 °C with or without the base permits, for the first time, the observation by 13C NMR spectroscopy of a bridging dioxalenium ion as an intermediate in a neighboring group directed glycosylation. Quenching of this cation in the presence of the base leads to the ortho ester, whereas in the absence of the base the glycosides are the only products detected.

show abstract

Section: Resultssupporting

confidence: 79%

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: ¹³C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

1999

View full text Add to dashboard Cite

show abstract

“…The signals corresponding to the phenyl ring protons of the dioxolanylium ion are clearly distinguishable from those in the starting material or product, being more deshielded [δ H 8.40–8.37 (2H/Ar- ortho ), 8.19–8.15 (1H/Ar- para ) and 7.82–7.78 (2H/Ar- meta )] compared to those in 3 [δ H 7.68–7.66 (2H) and 7.40–7.38 (3H)] and product 6 [δ H 8.03–8.01 (2H/Ar- ortho ), 7.74–7.70 (1H/Ar- para ) and 7.54–7.50 (2H/Ar- meta )]. In addition, fully in line with the values reported for similar dioxolanylium ions and α,α-dialkoxybenzyl cations, − the 13 C NMR spectrum of (±)- 15 also showed a signal attributable to C-2′ of the dioxolanylium ion at 183.3 ppm (Supporting Information, Figure 4).…”

Section: Resultssupporting

confidence: 86%

Regioselective Opening of myo-Inositol Orthoesters: Mechanism and Synthetic Utility

et al. 2013

View full text Add to dashboard Cite

Acid hydrolysis of myo-inositol 1,3,5-orthoesters, apart from orthoformates, exclusively affords the corresponding 2-O-acyl myo-inositol products via a 1,2-bridged five-membered ring dioxolanylium ion intermediate observed by NMR spectroscopy. These C-2-substituted inositol derivatives provide valuable precursors for rapid and highly efficient routes to 2-O-acyl inositol 1,3,4,5,6-pentakisphosphates and myo-inositol 1,3,4,5,6-pentakisphosphate with biologically interesting and anticancer properties. Deuterium incorporation into the α-methylene group of such alkyl ester products (2-O-C(O)CD2R), when the analogous alkyl orthoester is treated with deuterated acid, is established utilizing the novel orthoester myo-inositol 1,3,5-orthobutyrate as an example. Such deuterated ester products provide intermediates for deuterium-labeled synthetic analogues. Investigation into this selective formation of 2-O-ester products and the deuterium incorporation is presented with proposed mechanisms from NMR experiments.

show abstract

“…In this study, a 13 C-labeled tri- O -benzoyl xylopyranosyl thioglycoside was activated with benzenesulfenyl triflate in deuteriodichloromethane in both the presence and absence of the mild, sterically hindered base DTBMP at −78 °C. Direct observation of the reaction mixture by 13 C NMR spectroscopy at −78 °C revealed the formation of a single predominant species characterized by a sharp resonance at δ 180.3 assigned to the dioxalenium ion, consistent with literature chemical shift values for simple 2-phenyl-1,3-dioxalenium ions . When methanol was added to this ion formed in the presence of DTBMP, the signal at δ 180.3 was replaced by one at δ 121.1, taken as indicative of formation of an orthoester.…”

Section: Spectroscopic and Computational Identification Of Intermediatesmentioning

confidence: 90%

“…Direct observation of the reaction mixture by 13 C NMR spectroscopy at −78 °C revealed the formation of a single predominant species characterized by a sharp resonance at δ 180.3 assigned to the dioxalenium ion, consistent with literature chemical shift values for simple 2-phenyl-1,3-dioxalenium ions. 166 When methanol was added to this ion formed in the presence of DTBMP, the signal at δ 180.3 was replaced by one at δ 121.1, taken as indicative of formation of an orthoester. On the other hand, when methanol was added to a solution of the dioxalenium ion prepared in the absence of the base, no orthoester was observed suggesting that the β-glycoside was formed directly (Scheme 16).…”

Section: Spectroscopic and Computationalmentioning

confidence: 99%

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

et al. 2020

View full text Add to dashboard Cite

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.

show abstract

Structures of Some Dialkoxyphenylmethylium Ions; Steric Inhibition of Resonance

Cited by 10 publications

References 0 publications

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: ¹³C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: ¹³C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

Regioselective Opening of myo-Inositol Orthoesters: Mechanism and Synthetic Utility

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

Contact Info

Product

Resources

About

Structures of Some Dialkoxyphenylmethylium Ions; Steric Inhibition of Resonance

Cited by 10 publications

References 0 publications

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: 13C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: 13C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

Regioselective Opening of myo-Inositol Orthoesters: Mechanism and Synthetic Utility

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

Contact Info

Product

Resources

About

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: ¹³C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion

On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: ¹³C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion