Oxatriquinane and Oxatriquinacene: Extraordinary Oxonium Ions

Mascal, Mark; Hafezi, Nema; Meher, Nabin K.; Fettinger, James C.

doi:10.1021/ja805686u

Cited by 46 publications

(40 citation statements)

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“…For example, H 4 O 2+ is no longer a minimum energy structure in reaction fields with ε ≥ 3 in a continuum solvent model. 17 Also, examination of the reported, energy minimized structure of Me 3 OH 2+ reveals C–O bond lengths of 1.67 Å. The analogous Et 3 OH 2+ , which has also been implicated in the alkylation of aromatics, 15 has even less plausible C–O bond lengths of 1.74 Å and does not optimize to a minimum energy structure in the gas phase.…”

Section: Introductionmentioning

confidence: 99%

The R₃O⁺···H⁺ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

et al. 2011

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Oxatriquinanes are tricyclic oxonium ions which are known to possess remarkable solvolytic stability compared to simple alkyl oxonium salts. Their rigid, hemispherical structure presents an oxygen at the apex of three fused five-membered rings. While trivalent oxygen species like these have been well described in the literature, the ability of oxygen to enter into a fourth covalent bonding relationship has been visited in theory and suggested by the outcome of certain reactions conducted in superacidic media, but has never established by the characterization of a stable, persistent R3OH++ or R4O++ ion. In this study, the nucleophilicity of the oxatriquinane oxygen was evaluated first by a series of protonation studies using the Brønsted superacid H(CHB11Cl11) both in the solid state and in liquid HCl solution. The interaction of the oxatriquinane oxygen with a bridging carbocation was also examined. A strong case could be made for the occurrence of hydrogen bonding between H(CHB11Cl11) and oxatriquinane using IR spectroscopy. Under the most forcing protonation conditions, the oxatriquinane ring is cleaved to give a bridged, dicationic protonated tetrahydrofuran-carbenium ion.

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Section: Introductionmentioning

confidence: 99%

The R₃O⁺···H⁺ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

et al. 2011

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“…When the mechanical stretching is considered as quite evident and is largely discussed, the chemical stretching has not yet received enough attention. This explains the astonishment shown by the detection of 'abnormally' long bonds, as in the case of single C-C [8] and C-O [9,10] bonds. In fact, the elongated sg eq R of 1.647 Å, 1.659 Å, and 1.704 Å for C-C bond [8] as well as of 1.54 Å [9] and 1.622 Å [10] for C-O bond fall in the first quarter of the bond sg W cov regions as follows from Table 1 and Fig.…”

Section: Quantum-chemical Aspect Of Bond Stretchingmentioning

confidence: 98%

Stretching and Breaking of Chemical Bonds, Correlation of Electrons, and Radical Properties of Covalent Species

Sheka

2015

Advances in Quantum Chemistry

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“…Recently, Mascal et al reported the synthesis of oxatriquinane 2 and oxatriquinacene 3, which have a tricyclic condensed ring structure with an oxygen cationic center. 4) Compound 2 was isolated as a crystalline solid suitable for X-ray crystal structure analysis. Interestingly, 2 could be purified by column chromatography and was stable under reflux in alcohol or water.…”

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Functionalized Oxatriquinanes and Their Structural Equilibrium in Protic Solvent

Suzuki

Muratake

2014

CHEMICAL & PHARMACEUTICAL BULLETIN

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We synthesized oxatriquinane hexafluorophosphate bearing an ethoxycarbonylmethyl group 7 or a 2-oxopropyl group 11. Both of these organic oxonium cation compounds were obtained as stable solids. However, 1 H-NMR analysis showed that oxatriquinane 7 was present as the oxonium cation in aprotic solvent CD 3 CN, but was in rapid equilibrium with ring-opened bicyclic compound 8 in protic solvent CD 3 OD. The oxatriquinane 11 also showed similar behavior in protic solvent. Phenyl-substituted oxatriquinanes 12 and 14 were also obtained as stable solids, and showed similar properties to 7 and 11. Key words oxatriquinane; organic oxonium cation; equilibrium; protic solventThere have been few reports on stable organic oxonium salts, 1) though alkyl oxonium salts such as triethyl oxonium tetrafluoroborate 1 (known as Meerwein's reagent) have been utilized in organic synthesis as powerful alkylation reagents for alcohol or amine 2,3) ( Fig. 1). However, they are chemically unstable and sensitive to moisture, so they are difficult to handle. Recently, Mascal et al. reported the synthesis of oxatriquinane 2 and oxatriquinacene 3, which have a tricyclic condensed ring structure with an oxygen cationic center. 4)Compound 2 was isolated as a crystalline solid suitable for X-ray crystal structure analysis. Interestingly, 2 could be purified by column chromatography and was stable under reflux in alcohol or water. Subsequently, they synthesized several oxatriquinanes with simple alkyl groups and carried out X-ray crystal structure analysis.5,6) A unique S N 2 reaction at tertiary carbon in the α-position to the oxygen center was also reported.7) Most recently, oxatriquinane having a hydroxy group at the α-position to oxygen (4) was found to have the longest C-O bond length so far reported among organic compounds. 8)We became interested in these stable oxonium cation species, and set out to synthesize further examples for examination of their potential utility in materials science or medicinal chemistry.First, we focused on oxatriquinane having a simple ester group, to see whether such a group is compatible with the oxonium cation. As shown in Chart 1, the starting ketone 5, 7) which was synthesized from 1,5-cyclooctadiene, was subjected to Reformatsky reaction to afford β-hydroxyester 6 in good yield. Compound 6 was obtained as nearly a single stereoisomer, and its stereochemistry was determined by examination of the nuclear Overhauser effect (NOE) between methine proton at C1 and methylene protons at the α-position to the carbonyl group. Next, 6 was treated with trifluoromethanesulfonic acid (TfOH) in acetonitrile to give oxatriquinane trifluoromethanesulfonate, but we could not obtain this in crystalline form, so the salt was purified by simple anion exchange using sat. aqueous KPF 6 to afford oxatriquinane hexafluorophosphate 7 in an excellent yield as a stable off-white solid after usual work-up. Recrystallization from CH 2 Cl 2 /Et 2 O afforded colorless fine needles. Compound 7 showed good solubility in acetonitrile, dichlo...

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Oxatriquinane and Oxatriquinacene: Extraordinary Oxonium Ions

Cited by 46 publications

References 13 publications

The R₃O⁺···H⁺ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

The R₃O⁺···H⁺ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

Stretching and Breaking of Chemical Bonds, Correlation of Electrons, and Radical Properties of Covalent Species

Functionalized Oxatriquinanes and Their Structural Equilibrium in Protic Solvent

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Oxatriquinane and Oxatriquinacene: Extraordinary Oxonium Ions

Cited by 46 publications

References 13 publications

The R3O+···H+ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

The R3O+···H+ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

Stretching and Breaking of Chemical Bonds, Correlation of Electrons, and Radical Properties of Covalent Species

Functionalized Oxatriquinanes and Their Structural Equilibrium in Protic Solvent

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The R₃O⁺···H⁺ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion

The R₃O⁺···H⁺ Hydrogen Bond: Toward a Tetracoordinate Oxadionium(2+) Ion