Alkali Metals

Beswick, Michael A.; Wright, Dominic S.

doi:10.1016/b978-008046519-7.00001-0

Cited by 36 publications

(28 citation statements)

References 283 publications

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“…Lithium organic compounds are some of the most extensively investigated compounds in main group organometallic chemistry because of their many applications in research laboratories and industry. − In addition, the investigation of solid-state structures is important for our understanding of chemical bonding. Over 90% of the known studies of solid-state structures in this field were carried out on Lewis base adducts with nitrogen-, oxygen-, or sulfur containing ligands .…”

Section: Introductionmentioning

confidence: 99%

Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction

1998

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The solid-state structure of unsolvated, Lewis base-free phenyllithium (LiC 6 H 5 ) is reported. Structure determination of the simplest lithium aryl was performed by high-resolution synchrotron X-ray powder diffraction. The structure was solved by ab initio methods in combination with difference Fourier analysis and consecutive Rietveld refinements. Solid phenyllithium consists of dimeric Li 2 Ph 2 molecules, which strongly interact with adjacent Li 2 Ph 2 moieties, forming a polymeric, infinite-ladder structure along the crystallographic b-axis. In the Li 2 Ph 2 units the two lithium atoms and the C(ipso) atoms of the two phenyl rings form an absolutely planar, four-membered ring with the two phenyl rings perpendicular to it. The bonding of the C(ipso) atom to the two Li atoms can be described as a three-center, two-electron bond (Li-C 2.24(1) and 2.32(1) Å; Li-C-Li′ 63.2(7)°). The π-electrons of the phenyl rings interact strongly with the lithium atoms of neighboring Li 2 Ph 2 moieties.

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Section: Introductionmentioning

confidence: 99%

Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction

1998

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“…Lithium organometallic compounds are of special interest to organometallic chemists because of their widespread use in chemical laboratories and in industry applications. − Since the solid-state structures of the fundamental compounds [LiMe] 4 and [LiEt] 4 have been determined by X-ray diffraction experiments, , few structures of binary organolithium compounds (compounds formed between lithium cations and hydrocarbon anions without other neutral ligands) have been reported. Several years ago, Stalke et al were able to solve the single-crystal structures of the alkyllithium compounds [Li n Bu] 6 and [Li t Bu] 4 .…”

Section: Introductionmentioning

confidence: 99%

Solid-State Structures of Base-Free Indenyllithium and Fluorenylsodium

et al. 1999

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The solid-state structures of two important organometallic reagents, base-free indenyllithium and base-free fluorenylsodium, were determined by high-resolution X-ray powder diffraction experiments. Indenyllithium crystallizes as an infinite chain in the fashion of a “multidecker structure”, whereas fluorenylsodium forms the saltlike structure Na2[NaFl3], containing the novel trigonal [NaFl3]2- anion.

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“…17 It was hoped that addition of coordinating additives, such as multidentate ethers and amines, would break up these aggregates and accelerate the reaction. The requirement for substoichiometric base should ultimately allow the use of substoichiometric ligand.…”

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confidence: 99%

“…In order to develop a ligand-accelerated version of this methodology on which to base a potential catalytic asymmetric variant, attention was focussed on the reaction of lithium pyrrolate (12) with conjugate acceptors in toluene since lithiated organic molecules form highly aggregated structures in such solvents. 17 It was hoped that addition of coordinating additives, such as multidentate ethers and amines, would break up these aggregates and accelerate the reaction. The requirement for substoichiometric base should ultimately allow the use of substoichiometric ligand.…”

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confidence: 99%

“…The necessity for tridentate ligands suggests that monomeric lithium pyrrolate is the reactive species and not higher aggregates. 17 To demonstrate that this reaction offered potential for a catalytic asymmetric method, it was necessary to determine whether catalytic turnover of both lithium pyrrolate (12) and ligand could be achieved. Notably, the use of lithium pyrrolate in THF had resulted in no catalytic turnover.…”

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confidence: 99%

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Pyrrolate-Catalyzed Conjugate Addition of Pyrrole to Electron-Deficient Alkenes

Hernandez-Juan¹,

Dixon²

2006

Synlett

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The conjugate addition of pyrrole as a nitrogen nucleophile can be catalyzed by potassium pyrrolate in coordinating solvents or by lithium pyrrolate in the presence of coordinating ligands offering an efficient route to protected b-amino carbonyl compounds.b-Amino carbonyl compounds are key components in many biologically active natural and unnatural products such as taxol, 1 streptothricin F 2 and the renin inhibitor KR1 1314. 3 They are also useful precursors to the b-lactam motif found in the antibiotics penicillin and cephalosporin. 4 In recent years there has been much development in stereoselective methods of synthesis of bamino acids. 5 One of the most attractive and powerful strategies is the conjugate addition of nitrogen-centered nucleophiles to a,b-unsaturated carbonyl compounds and other electron-deficient alkenes. 6,7 Scheme 1 Proposed catalytic cycle Towards our aim of developing a conjugate addition of nitrogen nucleophiles using substoichiometric base for use in b-amino carbonyl synthesis, we focused on the conjugate addition of pyrrole (1) to enoates 2. 8 The reaction (Scheme 1) appeared to offer considerable scope for employment of substoichiometric base since, from studying the pK a values (quoted here in DMSO as a model aprotic solvent), it was predicted that pyrrole (1, pK a = 23) 9 would be rapidly deprotonated by the intermediate enolate 3 (pK a = 30), 10 regenerating the catalytic metal pyrrolate 4 and releasing the adduct 5. The results (Table 1) show that this was indeed the case for a range of a,b-unsaturated tert-butyl esters when substoichiometric potassium pyrrolate was used in the presence of excess pyrrole in chilled THF, giving excellent yields of the adducts 5a-e for all but the most hindered of substrates. 11,12 The lower yields for 5e (R = t-Bu) can be explained by increased steric hindrance at the b-carbon giving rise to reduced reaction rates. For the reaction with tert-butyl crotonate (entry a), it was found necessary to maintain the reaction temperature below 0°C, and reduce the reaction time, in order to prevent formation of an unwanted bisadduct 6 ( Figure 1) believed to arise from a competing carbonyl substitution pathway. Interestingly, this was not seen with any of the other tert-butyl ester substrates. However, with less sterically demanding ester groups, such as ethyl crotonate, ester aminolysis was a major pathway.The potassium pyrrolate-catalyzed conjugate addition of pyrrole is general to a range of a,b-unsaturated substrates ( Table 2). Of interest are the nitrile 7 and Weinreb amide 9 since they allow access to both aldehyde 13 and ketone 14

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Alkali Metals

Cited by 36 publications

References 283 publications

Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction

Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction

Solid-State Structures of Base-Free Indenyllithium and Fluorenylsodium

Pyrrolate-Catalyzed Conjugate Addition of Pyrrole to Electron-Deficient Alkenes

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