η1‐(1S,2E)‐1‐(N, N‐Diisopropylcarbamoyloxy)‐3‐trimethylsilyl‐allyllithium‐(‐)‐Spartein: Struktur einer chiralen, Carbamoyloxy‐substituierten Allyllithium‐Verbindung

Marsch, Michael; Harms, Klaus; Zschage, Oliver; Hoppe, Dieter; Boche, Gernot

doi:10.1002/ange.19911030327

Cited by 61 publications

(13 citation statements)

References 40 publications

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“…With a few exceptions, a large number of the cases involve benzyl, allyl, or cinnamyl organolithium reagents which are capable of delocalizing the negative charge over several atoms. Although such intermediates are usually distorted from an ideal tetrahedral geometry, the X‐ray crystal structures of 55 (Scheme ) and 87 (Scheme ) indicate that the carbanion center retains a small degree of pyramidalization and is not completely planar 61, 97. Planarization serves to reduce the steric difference between the front and back faces of the carbanion, although the presence of an external ligand perturbs that symmetry.…”

Section: Stereochemistry Of Electrophilic Substitutionmentioning

confidence: 99%

“…One of the biggest challenges towards understanding the nature of electrophilic substitution derives from the scarcity of structural information on the organolithium reagents. Only two of the organolithium species in Table 3 (entries 5 and 6) have been characterized structurally by means of X‐ray crystallography 61, 97. Both crystallize as monomers bound to the bulky (−)‐sparteine ligand, which effectively blocks the syn face of the organolithium compound.…”

Section: Stereochemistry Of Electrophilic Substitutionmentioning

confidence: 99%

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

Basu

Thayumanavan

2002

Angew. Chem. Int. Ed.

232

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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.

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Section: Stereochemistry Of Electrophilic Substitutionmentioning

confidence: 99%

Section: Stereochemistry Of Electrophilic Substitutionmentioning

confidence: 99%

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

Basu

Thayumanavan

2002

Angew. Chem. Int. Ed.

232

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“…This is also true for (−)-sparteine complexes, although a possible large difference in the rates has not yet been investigated more closely 226 …”

Section: Preparation and Structurementioning

confidence: 79%

“…An X-ray crystal structure analysis was obtained from the 3-(trimethylsilyl)-allyllithium-(−)-sparteine complex (S)-302b 226 . It reveals the monomeric structure of these allyllithium compounds and a η 1 -coordination of the allylic anion to the lithium cation.…”

Section: Preparation and Structurementioning

confidence: 99%

“…Ti(OPr-i) 3 (R)-(334a) Some alkenyl carbamates leading to configurationally labile lithium intermediates could be subjected to asymmetric homoaldol reaction with less efficiency (Scheme 6); these reactions have not been optimized yet 224,226 . The titanium compounds, derived from the configurationally stable lithium-(−)-sparteine complexes 349a,b prepared from primary allyl carbamates, undergo lithium-titanium exchange with chlorotriisopropoxytitanium to form the allyltitanates 228 .…”

Section: Me Ocbmentioning

confidence: 99%

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Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

Hoppe

Christoph

2009

Patai's Chemistry of Functional Groups

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Introduction Non‐Mesomerically Stabilized Organolithium Compounds (−)‐Sparteine‐Induced Lithiation with Formation of Benzyl‐Type Organolithiums Allyllithium–(−)‐Sparteine Complexes Lithium–(−)‐Sparteine Complexes of 2‐Alkynyl Carbamates Axial–Chiral and Planar–Chiral Lithium–(−)‐Sparteine Complexes Enantioselective Addition of Achiral Carbanionic Compounds in the Presence of (−)‐Sparteine

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Sulfonyl-Stabilized Allylic Norbornenyl and Norbornyl Carbanions: Structure and Stereoselectivity of Reaction with Electrophiles

Gais¹,

Gumpel

Raabe

et al. 1999

Eur. J. Org. Chem.

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The structures of the norbornenyl and norbornyl sulfones exo‐5, endo‐5 and endo‐6 have been determined experimentally, by X‐ray analysis, and theoretically by ab initio calculations (HF/6–31+G*). X‐ray crystal structure analyses of the lithiated allylic norbornenyl and norbornyl sulfones endo‐3/ent‐endo‐3·2diglyme and endo‐4/ent‐endo‐4·2diglyme revealed dimeric O–Li contact ion pairs devoid of C–Li bonds. The anions of endo‐3/ent‐endo‐3·2diglyme and endo‐4/ent‐endo‐4·2diglyme adopt both the endo conformation (C2–S) and are characterized by in the exo direction pyramidalized anionic C atoms. The degree of pyramidalization of the C2 atom of 3 is higher than that of 4. Ab initio optimizations (HF/6–31+G*) of the structures of the anions of methylenenorbornene I and methylenenorbornane II resulted in local minima featuring non‐planar C2 atoms which are pyramidalized in the exo direction in both cases, but to different degrees. In both cases cryoscopy of 3 and 4 in THF at –108.5 °C revealed approximately 1:1 mixtures of monomers and dimers. The sulfones exo‐5, endo‐5, exo‐6 and endo‐6 as well as the lithiosulfones 3 and 4 were studied by NMR spectroscopy. 1H‐NMR (400 MHz), 13C‐NMR (100 MHz) and 6Li‐NMR (44 MHz) spectroscopy of 3 and 4 at –100 °C in [D]8THF revealed in each case only one set of signals, independent of the configuration of the starting sulfones. This indicates in both cases that attainment of both the monomer‐dimer and the endo/exo equilibria of 3 and 4 is fast on the NMR time scale. According to 6Li{1H}‐ and 1H{1H}‐NOE experiments of 3 and 4 the monomeric and dimeric species endo‐3 and endo‐4, having endo anions, seem to be preferred in THF solution. Ab initio calculations of the anions of 3 and 4 resulted in structures endo‐3(–Li+), exo‐3(–Li+), endo‐4(–Li+) and exo‐4(–Li+) (HF/6–31+G*), whose atomic point charges were calculated by the method of Kollman et al. The C2 atoms of endo‐3(–Li+) and endo‐4(–Li+) are pyramidalized in the exo direction whereas the C2 atoms of exo‐3(–Li+) and exo‐4(–Li+) are pyramidalized in the endo direction. According to the calculations, the endo anions are more stable than the exo anions. There is good agreement between the optimized structures of the free anions and the experimentally determined structures of the anions of the contact ion pairs in the crystal. Reactions of 3 and 4 with DX, MeI, EtI, nPrI and nHeI occurred at the C2 atom under the selective formation of the corresponding endosulfones endo‐8a–e and endo‐9a–e, respectively, in all cases. Thus, an earlier report on the selective formation of the exosulfone exo‐9b in the reaction of 4 with MeI has to be revised. Product ratios were independent of the configuration of the starting sulfones and varied with the nature of the electrophile. Selectivities were highest in the case of the norbornyl species 4. Reaction of 3 with PhCHO occurred at the α position (C2) to afford the alcohols endo‐8f and exo‐8f (88:12) as single diastereomers and at higher temperatures at the γ position (C8), whereas reaction of ...

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η¹‐(1S,2E)‐1‐(N, N‐Diisopropylcarbamoyloxy)‐3‐trimethylsilyl‐allyllithium‐(‐)‐Spartein: Struktur einer chiralen, Carbamoyloxy‐substituierten Allyllithium‐Verbindung

Cited by 61 publications

References 40 publications

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

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

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

Sulfonyl-Stabilized Allylic Norbornenyl and Norbornyl Carbanions: Structure and Stereoselectivity of Reaction with Electrophiles

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