Rational Design of Chiral Lithium Amides for Asymmetric Alkylation Reactions—NMR Spectroscopic Studies of Mixed Lithium Amide/Alkyllithium Complexes

Arvidsson, Per I.; Hilmersson, Göran; Davidsson, Öjvind

doi:10.1002/(sici)1521-3765(19990802)5:8<2348::aid-chem2348>3.3.co;2-1

Cited by 17 publications

(29 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In addition there are two more signals at δ =2.09 and δ =3.23 (in a 1:1 ratio) arising from a mixed dimer ( 1 ‐[ 6 Li])/ n Bu[ 6 Li]. We conclude that in agreement with previous findings on similar lithium amides, 1 ‐[ 6 Li] forms mixed dimers with n Bu[ 6 Li] in Et 2 O 12…”

Section: Resultssupporting

confidence: 91%

“…( S )‐ N ‐Isopropyl‐ O ‐methyl‐valinol : The ( S )‐ N ‐isopropyl‐ O ‐methyl‐valinol was prepared according to published procedures: LiAlH 4 reduction of D ‐valine to D ‐valinol,10 methylation by MeI to afford the amino methyl ether,11 condensation with acetone to the corresponding imine and finally reduction using H 2 /Pd/C in a Parr apparatus at 4 atm 12…”

Section: Methodsmentioning

confidence: 99%

“…Williard and Sun suggested that if such trimeric complexes are present they could be responsible for the asymmetric alkylation reactions. Closely related lithium amides have been reported to yield enantioselectivities over 90 % in the butylation of aldehydes 5c, 9…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mixed Dimer and Mixed Trimer Complexes ofnBuLi and a Chiral Lithium Amide

Hilmersson

Malmros

2001

Chem. Eur. J.

Self Cite

View full text Add to dashboard Cite

Multinuclear and multidimensional NMR spectroscopy have shown that lithium (S)-N-isopropyl-O-methyl-valinol (1-[6Li]) exists in a mixed 2:1 complex with nBu[6Li], (1-[6Li])2/nBu[6Li], in non-coordinating solvents such as hexane or toluene. A 6Li,1H-HOESY NMR spectrum indicates that the complex is a cyclic trimer with a large distance between the di-coordinated lithium and the carbanion of nBu[6Li]. Such arrangements are present in the solid state as previously reported by Williard and Sun. The exchange of lithium atoms within the trimer is slow at -33 degrees C. The exchange barrier (deltaG++) was determined to be 14.7 kcal x mol(-1) from quantitative 6Li,6Li-EXSY spectra. Addition of diethyl ether results in the formation of mixed dimers of (1-[6Li])/nBu[6Li], tetramers of nBu[6Li], and homodimers (1-[6Li])2. The apparent equilibrium constant of the mixed dimer was determined from the 6Li NMR integrals as K = 7.

show abstract

Section: Resultssupporting

confidence: 91%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Mixed Dimer and Mixed Trimer Complexes ofnBuLi and a Chiral Lithium Amide

Hilmersson

Malmros

2001

Chem. Eur. J.

Self Cite

View full text Add to dashboard Cite

show abstract

“…We believe that the first of these challenges is the development of a systematic structure–function relationship for the stereochemical behavior of organolithium compounds. There have only been a few instances in which structural information about organolithium aggregates have been used as the starting point for the design of stereoselective lithiation/substitution sequences 151, 152. A second and more challenging goal is the development of catalytic processes that use organolithium reagents.…”

Section: Discussionmentioning

confidence: 99%

Configurational Stability and Transfer of Stereochemical Information in the Reactions of Enantioenriched Organolithium Reagents

Basu

Thayumanavan

2002

Angew. Chem. Int. Ed.

232

View full text Add to dashboard Cite

The conversion of a prochiral methylene group into a stereogenic center by means of a lithiation/substitution sequence has emerged as a powerful synthetic transformation over the past 15 years. This reaction proceeds via a chiral organolithium intermediate, and the stereochemical fidelity of the overall reaction sequence is intimately dependent on the stereochemical behavior of the chiral organolithium as well as on the rate and stereochemical sense of the electrophilic substitution step. Chiral organolithium reagents were first reported by Letsinger, Curtin, and Applequist half a century ago. The lithiated intermediates in these early studies were not highly configurationally stable, and applications in stereoselective synthesis were not immediately forthcoming. The two decades that followed the 1980 report by Still and Sreekumar of a configurationally stable α‐oxyorganolithium were marked by an increased interest in these reagents. As the synthetic applications of chiral organolithium reagents have grown, so have accompanying mechanistic studies of these intermediates which serve as the basis for this review.

show abstract

“…Geburtstag gewidmet Chiral modifizierte lithiumorganische Reagentien haben für enantioselektive Synthesen [1] sowie als Initiatoren in asymmetrischen anionischen Polymerisationen [2] eine herausragende Bedeutung. [7] Obwohl n-Butyllithium (nBuLi) zu den meistverwendeten Lithiumorganylen zählt und einige Röntgenstrukturanalysen achiraler nBuLi-Komplexe bekannt sind, [8] liegen bisher nur sehr wenige Strukturuntersuchungen von chiral modifizierten nBuLi-Systemen vor. [3] Untersuchungen in Lösung [4] und im Festkörper [1a,g,h, 5] geben wertvolle Hinweise auf die Natur der chiralen Organolithiumsysteme [6] und eröffnen Möglichkeiten für ein rationales Design neuartiger Reagentien.…”

unclassified

Chirale Modifizierung vonn-Butyllithium: Steuerung von Stöchiometrie, Struktur und Enantioselektivität durch modulare Fencholat-Einheiten

2000

View full text Add to dashboard Cite

Professor Dr. Günter Helmchen zum 60. Geburtstag gewidmet Chiral modifizierte lithiumorganische Reagentien haben für enantioselektive Synthesen [1] sowie als Initiatoren in asymmetrischen anionischen Polymerisationen [2] eine herausragende Bedeutung. Die Kontrolle von Reaktivitäten und Selektivitäten durch geeignete chirale Moderatoren ist entscheidend für deren erfolgreichen Einsatz. [3] Untersuchungen in Lösung [4] und im Festkörper [1a,g,h, 5] geben wertvolle Hinweise auf die Natur der chiralen Organolithiumsysteme [6] und eröffnen Möglichkeiten für ein rationales Design neuartiger Reagentien. [7] Obwohl n-Butyllithium (nBuLi) zu den meistverwendeten Lithiumorganylen zählt und einige Röntgenstrukturanalysen achiraler nBuLi-Komplexe bekannt sind, [8] liegen bisher nur sehr wenige Strukturuntersuchungen von chiral modifizierten nBuLi-Systemen vor. [5b,c, 9] Vor kurzem berichteten wir über die Synthese und die Struktur des enantiomerenreinen nBuLi-Lithiumfencholat-Komplexes 1. [9] Er entsteht nach Mischen von o-Anisylfenchol 2 und nBuLi in Hexan als farbloser Niederschlag und enthält

show abstract

Rational Design of Chiral Lithium Amides for Asymmetric Alkylation Reactions—NMR Spectroscopic Studies of Mixed Lithium Amide/Alkyllithium Complexes

Cited by 17 publications

References 0 publications

Mixed Dimer and Mixed Trimer Complexes ofnBuLi and a Chiral Lithium Amide

Mixed Dimer and Mixed Trimer Complexes ofnBuLi and a Chiral Lithium Amide

Configurational Stability and Transfer of Stereochemical Information in the Reactions of Enantioenriched Organolithium Reagents

Chirale Modifizierung vonn-Butyllithium: Steuerung von Stöchiometrie, Struktur und Enantioselektivität durch modulare Fencholat-Einheiten

Contact Info

Product

Resources

About