NMR spectroscopy of organolithium compounds, Part XVI

Bergander, Klaus; He, Runxi; Chandrakumar, N.; Eppers, Oswald; Günther, H.

doi:10.1016/s0040-4020(01)90441-7

Cited by 34 publications

(22 citation statements)

References 27 publications

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“…400/58.9 MHz 1 H, 6 Li 2D‐HEHAHA spectrum of [ 6 Li]‐2,2‐[D 2 ] n ‐butyllithium ( 2.3 M in [D 8 ]dimethoxy methane at 200 K) measured with pulse sequence (a) of Fig. (see experimental part); spin lock time 0.81 s; under the conditions used n ‐butyllithium exists on the NMR time scale of the small 1 H, 6 Li coupling (<0.1 Hz) as a fluxional tetramer with intra ‐aggregate exchange and the coupling is time‐averaged over all four C α H 2 methylene groups.…”

Section: Nmr Data For 2[3a]mentioning

confidence: 99%

“…3b shows indeed, aside from a few minor absorptions, the relatively strong H(C α ) signal that documents the selective magnetization transfer via the heteronuclear 6 Li, 1 H coupling. Although the HEHAHA is designed for inphase transfer, it should be noted that transfer from a spin 1 nucleus to a spin ½ results in slightly distorted multiplets with side lobes [14,15] that sometimes can even result 6 Li coupling (<0.1 Hz) as a fluxional tetramer with intra-aggregate exchange [11] and the coupling is time-averaged over all four C α H 2 methylene groups.…”

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confidence: 99%

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A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs

Bergander

Hüls

Glaser

et al. 2014

Magnetic Reson in Chemistry

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Heteronuclear TOCSY (HEHAHA) experiments for (1) H,(6) Li spin pairs in organolithium compounds with adjacent strongly coupled (1) H,(1) H spin systems showed unexpected cross peak behaviour: for n-butyllithium (1) H,(6) Li cross peaks were completely missing, whereas for the dimer of (Z)-2-lithio-1-(o-lithiophenyl)ethane, a cross peak for remote protons was observed even at very short mixing times. It was assumed that strong magnetization transfer within the proton spin systems was responsible for these results, which prevented unambiguous chemical shift assignments. Selective experiments with the (6) Li,(1) H-HET-PLUSH-TACSY sequence then showed the expected (6) Li,(1) H cross peaks for the transfer via the directly coupled (1) H and (6) Li nuclei. For n-butyllithium transfer to H(Cα) via an unresolved heteronuclear coupling constant below 0.1 Hz is unambiguously observed. Cross peaks in the 2D (6) Li,(1) H-HET-PLUSH-TACSY spectra for the dimer of (Z)-2-lithio-1-(o-lithiophenyl)ethane are readily explained by the measured coupling network and the corresponding active mixing conditions.

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Section: Nmr Data For 2[3a]mentioning

confidence: 99%

mentioning

confidence: 99%

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs

Bergander

Hüls

Glaser

et al. 2014

Magnetic Reson in Chemistry

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“…[8] However, the situation is often more complicated as many organolithium compounds in ethereal solvents and in the presence of diamines or halides are likely to form mixtures of coexisting homo-and mixed aggregates. [10,11] Three oligomeric structures (see Scheme 1) have been reported for nBuLi: a hexamer in nonpolar hydrocarbon solvents, [12] a tetramer in diethyl ether and in dimethoxymethane, [13] and an equilibrium between the dimer and tetramer in THF. Furthermore, the outcomes of a wide variety of reactions can be explained by the complexation of an organolithium reagent to the substrate prior to the actual reaction.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the outcomes of a wide variety of reactions can be explained by the complexation of an organolithium reagent to the substrate prior to the actual reaction. [10,11] Three oligomeric structures (see Scheme 1) have been reported for nBuLi: a hexamer in nonpolar hydrocarbon solvents, [12] a tetramer in diethyl ether and in dimethoxymethane, [13] and an equilibrium between the dimer and tetramer in THF. [3a, 8, 14] An important consequence of the existence of several types of aggregates in solution and their different reactivities is that fractional reaction orders have been found, ranging from 0.25 to 1, in proton-transfer reactions promoted by butyllithium.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the Deprotonation Reaction of Alkyl Benzyl Ethers with n‐Butyllithium

Raposo¹,

Fernández‐Nieto

García‐Río³

et al. 2013

Chemistry A European J

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Kinetic study of the α-lithiation of benzyl methyl ether (BME) by nBuLi has revealed that increasing the concentration of the organolithium compound does not necessarily increase the reactivity, and this is a consequence of the reactivities of the different nBuLi aggregates present in solution. We propose a dimer-based mechanism, in which a pre-complexation step is a key process for substrates bearing a donor oxygen atom that can interact with the lithium cation to form mixed dimers. For these studies, we have developed a system based on UV/Vis spectroscopy that allows kinetic measurements to be conducted at -80 °C under argon.

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“…It turned out that the amount of the lithiating agent and ketone, and also the duration and the temperature of the reaction did not affect the diol yield. The replacement of ether by THF where the BuLi is known to be less associated than in ether [6] unexpectedly has resulted in signifi cant decrease in the yield (from 65 to 22%). There are published examples on improvement of the lithiation at the addition of the tetramethylethylenediamine [7].…”

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New chiral ligands: 1,4-diols prepared from (S)-1-phenylethanol

et al. 2010

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The stereochemistry of condensation of dilithiated 1-phenylethanol with various carbonyl compounds was investigated. In most cases the reaction proceeds nonstreoselectively, and only in the condensation with PhCOBu-t and 2,4-(MeO) 2 C 6 H 3 COPh only one of the diastereomeric diols prevailed. It was shown by XRD analysis that in the prevailing diastereomeric diol the newly formed chiral carbinol center possessed the same confi guration as the initial alcohol. The synthesized diols form homochiral dimers in the crystal lattice.The asymmetric synthesis of chiral organic compounds with a desired absolute confi guration of the atoms in the carbon skeleton takes a special place in the current organic synthesis. The growing world-wide interest in enantiomerically pure compounds is due to their practical value, mainly as components of new effi cient drugs. The enantiomers of a chiral biologically active substance often differently affect the body, and the infl uence may be not only neutral, but sometimes negative. The difference may be not only in the biological effect but also in the pharmacokinetics and in the metabolism of enantiomers [1].The main role in the synthesis of chiral compounds belongs nowadays to the asymmetric synthesis, and in particular, to the asymmetric catalysis. The main requirement to the chiral ligands is the presence of no less than two functional groups capable of the formation of a conformationally rigid transition complex, and the location of these groups close to the chiral center of defi nite conformation. And certainly, a very important problem is the availability of the optically active compound.One of the most important compound classes applied to the asymmetric synthesis are 1,4-diols. The main substances, BINOLs (I) and TADDOLs (II), proved to be highly effi cient asymmetry inducing catalysts for, e.g., the diethylzinc addition to aldehydes, the conjugate addition to unsaturated carbonyl compounds, the aldol reaction, the reactions of Diels-Alder, Strecker, Friedel-Krafts, reduction, and oxidation [2, 3].The example of the practical application of the (S)-BINOL is its employing as a complex with lanthanum in the synthesis of one of the key precursors of the fostriecin (exibiting a high anticancer action) that is a leading compound among the antitumor drugs [4].

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NMR spectroscopy of organolithium compounds, Part XVI

Cited by 34 publications

References 27 publications

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs

Mechanism of the Deprotonation Reaction of Alkyl Benzyl Ethers with n‐Butyllithium

New chiral ligands: 1,4-diols prepared from (S)-1-phenylethanol

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NMR spectroscopy of organolithium compounds, Part XVI

Cited by 34 publications

References 27 publications

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for 1H,6Li spin pairs

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for 1H,6Li spin pairs

Mechanism of the Deprotonation Reaction of Alkyl Benzyl Ethers with n‐Butyllithium

New chiral ligands: 1,4-diols prepared from (S)-1-phenylethanol

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A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs