Solution structure of a key intermediate used in asymmetric alkylation reactions. 1H, 1H-NOESY and 6Li, 1H-HOESY studies of mixtures of a chiral lithium amide and n-butyllithium

Hilmersson, Göran; Davidsson, Öjvind

doi:10.1016/0022-328x(94)05157-7

Cited by 65 publications

(26 citation statements)

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“…The in-situ preparation of (2-methoxy-(R)-1-phenyl-ethyl)-(2-[ 6 Li]-lithium-(S)-1-phenylethyl)amide and characterization has been reported previously. [8] NMR spectroscopy: All NMR spectra were recorded with a Varian Unity 500 spectrometer equipped with three channels and a 5 mm 1 H, 13 C, 6 Li triple-resonance probe head, built by the Nalorac company. Measuring frequencies were 500 MHz ( 1 H) and 125 MHz ( 13 C).…”

Section: Methodsmentioning

confidence: 99%

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An NMR and Computational Study of a Lithium Amide and Ethereal Ligand Exchange

Hilmersson¹

2000

Chem. Eur. J.

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The activation parameters for the exchange of an ethereal ligand in a chiral lithium amide was determined from full bandshape analysis of the dynamic NMR spectra. For diethyl ether, the activation parameters were deltaH++=11.0 kcalmol(-1) and deltaS++=12.0 cal K(-1)mol(-1). The exchange of the tetrahydrofuran ligand proceeds with a similar activation enthalpy deltaH++=11.2 kcalmol(-1); however, the entropy is close to zero. deltaS++=1.6 cal K(-1)mol(-1). The dissociation of the ethereal ligand was also modeled by means of semiempirical (PM3) and density functional (DFT) methods. The experimental 13C NMR chemical shifts for the carbons of uncoordinated and coordinated ethers were calculated with the GIAO-DFT (B3PW91/6-31G(d)) computational method.

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Section: Methodsmentioning

confidence: 99%

“…Dihedral angles[8] and energies[Hartree] for the different DEE conformations. Energies in Hartrees and kcal mol À1 are also given for the different conformations of DEE obtained at the B3LYP/6-31G(d)//B3LYP/ 6-31G(d) level of theory.…”

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An NMR and Computational Study of a Lithium Amide and Ethereal Ligand Exchange

Hilmersson¹

2000

Chem. Eur. J.

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“…The spectra recorded at that temperature showed small signals of the starting compound and a set of signals assigned to the anion 2a. The same experiment was carried out with n-Bu 6 Li [33] for recording the 6 Li NMR spectrum.…”

Section: Kinetic Measurementsmentioning

confidence: 99%

Metalation of 9‐Oxabicyclo[3.3.1]nonadiene – the Deprotonation Path to Bridgehead Olefins

Bassioni

Köhler

2006

Eur J Org Chem

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A new route to bridgehead olefins based on a deprotonation reaction has been established. The deprotonation of 9-oxabicyclo[3.3.1]nonadiene (1) with tBuLi/TMEDA occurs selectively in the allylic position. Whilst 1 has four allyl positions, only one bridgehead proton was removed, as demonstrated by quenching with Me 3 SnCl, Me 3 SiOTf, and Me 3 PbCl. With a threefold excess of deprotonating agent and subsequent treatment with Me 3 SnCl, three stannylated derivatives -3, 4a, and 4b -were obtained. Compound 3 is the starting diene 1 substituted at the bridgehead position 1 in the skeleton, and when smaller quantities of deprotonating agent were used it was the only stannylated derivative of 1 formed. Compounds 4a and 4b had each undergone a shift of one double bond to give bridgehead olefins exo-and endo-stannylated at position 3 in the skeleton. The common intermediate pre-

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“…42 Hilmersson and Davidsson studied, by means of intensive NMR investigations, a mixed 1:1 complex of n-BuLi and the lithiated methoxyamine 6 ( Figure 1) in diethyl ether at -80°C. 43 A fluxional exchange between tetrameric and dimeric structures of the chiral lithiated pyrrolidine 13 and n-BuLi is apparent in diethyl ether solution. 44 With the lithiated amine 14, a derivative of 6, (S)-1-phenyl-1-pentanol (75% ee) was obtained in n-BuLi additions to Ph-CHO, using a ratio of 1.0:0.45:0.25 in diethyl ether at -116°C.…”

Section: Biographical Sketchmentioning

confidence: 99%

Organolithiums in Enantioselective Additions to π* and σ* Carbon-Oxygen Electrophiles

Goldfuß¹

2005

Synthesis

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Mediated by chiral, non-racemic ligands, organolithiums add enantioselectively to C=O functions of carbonyl compounds (aldehydes and ketones) or cleave enantioselectively C-O units in strained ethers (epoxides and oxetanes) as well as in acetals. The achievement of high enantioselectivities is desirable and hence factors controlling these enantioselectivities are the subject of intensive research. Beneficial external influences on enantioselectivity are low temperatures, suitable solvents (e.g. dimethoxymethane, dimethyl ether) and the exclusion of salt impurities. Organolithium reagents and ligands lithiated in situ form mixed anionic aggregates, some of which can be isolated and even structurally studied. The improved understanding of the nature of such chiral organolithium aggregates provides the way to a more rational design of new enantioselective organolithium reagents.

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Solution structure of a key intermediate used in asymmetric alkylation reactions. 1H, 1H-NOESY and 6Li, 1H-HOESY studies of mixtures of a chiral lithium amide and n-butyllithium

Cited by 65 publications

References 9 publications

An NMR and Computational Study of a Lithium Amide and Ethereal Ligand Exchange

An NMR and Computational Study of a Lithium Amide and Ethereal Ligand Exchange

Metalation of 9‐Oxabicyclo[3.3.1]nonadiene – the Deprotonation Path to Bridgehead Olefins

Organolithiums in Enantioselective Additions to π* and σ* Carbon-Oxygen Electrophiles

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