Struktur eines chiralen Lithium‐azaenolats: monomeres, intramolekular chelatisiertes Lithio‐2‐acetylnaphthalin‐SAMP‐hydrazon

Enders, Dieter; Bachstädter, Gerhard; Kremer, Kenneth A. M.; Marsch, Michael; Harms, Klaus; Boche, Gernot

doi:10.1002/ange.19881001117

Cited by 39 publications

(3 citation statements)

References 15 publications

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“…The resulting partial double-bond character of the N -C(11) bond is reflected by its length 1.380(1) 8,. It causes an increased weight of the p-quinonoid resonance structure of the phenyl ring, as suggested by the reduced intraannular angles (Table 1) at C(11) and C (14) and the widened angles at C(12), C( 16), C( 1 3), and C( 1 5). Figure 2 shows the dimer 1 in a view parallel to the planes of the anilide anions, which clarifies their relation to the lithium cations.…”

Section: A N-(22-dimethyl-l-methylenepropyl)-nlithiobenzenamine (L)mentioning

confidence: 96%

Molecular Structures of a Lithiated Schiff Base and a Related Dialkyl Ketone Imine

Knorr¹,

Dietrich

Mahdi

1991

Chem. Ber.

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The ether-solvated lithium derivative of pinacolone anil (2a) is shown to be a centrosymmetric dimer (1) by X-ray diffraction analysis. Each lithium atom is bound to two nitrogen atoms, to the oxygen atom of diethyl ether, and weakly to two carbon atoms of a phenyl ring, but not to the vinyl moiety of the enamide anion. Despite conformational deconjugation, 1 is methylated at the carbon atom by methyl iodide. 'H-NMR shifts of 1 in solution are solvent-dependent. The results are discussed with respect to the "syn effect" in 1-azaallyl anions. The molecular structure of the dianil 3 of 2,2,?,?-tetramethyl-3,6-octanedione shows that a CH proton may approach the n face of an aromatic carbon atom down to a nonbonding distance of 2.74 8, without causing much strain.

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Section: A N-(22-dimethyl-l-methylenepropyl)-nlithiobenzenamine (L)mentioning

confidence: 96%

Molecular Structures of a Lithiated Schiff Base and a Related Dialkyl Ketone Imine

Knorr¹,

Dietrich

Mahdi

1991

Chem. Ber.

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“…[c] In the meantime, the dimeric Li phenylacetonitrile-TMEDA complex solvated by one molecule of benzene per aggregate unit was isolated and successfully subjected to X-ray crystal structure analysis 1961. [dl For the crystal structure of the Li enehydrazide of the hydrazone obtained from 2-naphthyl methyl ketone and N-aminoprolinol methyl ether, see [97] (monomeric, with two T H F oxygens and the oxygen of the prolinol ether unit surrounding the Li atom).…”

Section: Enolates and "Ingredients" In The Crystalline Statementioning

confidence: 99%

Structure and Reactivity of Lithium Enolates. From Pinacolone to Selective C‐Alkylations of Peptides. Difficulties and Opportunities Afforded by Complex Structures

Seebàch¹

1988

Angew. Chem. Int. Ed. Engl.

843

277

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The chemistry of lithium enolates is used to demonstrate that complex structures held together by noncovalent bonds ("supramolecules") may dramatically influence the result of seemingly simple standard reactions of organic synthesis. Detailed structural data have been obtained by crystallographic investigations of numerous Li enolates and analogous derivatives. The most remarkable features of these structures are aggregation to give dimers, tetramers, and higher oligomers, complexation of the metal centers by solvent molecules and chelating ligands, and hydrogen-bond formation of weak acids such as secondary amines with the anionoid part of the enolates. The presence in nonpolar solvents of the same supramolecules has been established by NMR-spectroscopic, by osmometric, and by calorimetric measurements. The structures and the order of magnitude of the interactions have also been reproduced by ab-initio calculations. Most importantly, supramolecules may be product-forming species in synthetic reactions of Li enolates. A knowledge of the complex structures of Li enolates also improves our understanding of their reactivity. Thus, simple procedures have been developed to avoid complications caused by secondary amines, formed concomitantly with Li enolates by the common methods. Mixtures of achiral Li enolates and chiral Li amides can give rise to enantioselective reactions. Solubilization by LiX is observed, especially of multiply lithiated compounds. This effect is exploited for alkylations of N-methylglycine (sarcosine) CH2 groups in open-chain oligopeptides. Thus, the cyclic undecapeptide cyclosporine, a potent immunosuppressant, is converted into a THF-soluble hexalithio derivative (without epimerization of stereogenic centers) and alkylated by a variety of electrophiles in the presence of either excess lithiumdiisopropyl amide or of up to 30 equivalents of lithium chloride. Depending on the nature of the LiX additive, a new stereogenic center of ( R ) or ( S ) configuration is created in the peptide chain by this process. A structure-activity correlation in the series of cyclosporine derivatives thus available is discussed.Nowadays, the molecular program of chemistry has arrived at its successful termination.

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“…25.98 (C-3). 26.57 (C-G'), 29.56 (C-l"'), 30.13 (C-3'), 46.37 (C-1"), 48.31 (C-2'), 54.61 ( C -j ) 1-2-(riietho.~~imetl~yl) 26.24 (CH2CHZCH2CH2CHlCH),26.73,27.12 (CH2CHlCHzCH2CH2CH),CH), 30.32 (C-3' (20) [ChH,f] 1-2-(metho~ytnet1iyl) 26.18 (C-5"). 29.09 (C-3'), 30.10 ( C -6 ) , 30.31 (C-4"), 32.59 (C-5'), 37.96 (C-3"), 47.09 (C-1"), 52.54 (C-2'), 53.59 (C-5) 26.14 (C-3), 27.04 (C-5"), 28.59 (C-6"), 28.87 (C-4"), 38.46 (C-3"), 48.40 (C-2'), 49.61 (C-l'), 52.98 (C-5) …”

Section: (Srr):(sss):(ssr):(s~s)]mentioning

confidence: 99%

The First Asymmetric Carroll Rearrangement Diastereo‐ and Enantioselective Synthesis of Polyfunctional Ketones with Vicinal Quaternary and Tertiary Stereogenic Centers

et al. 1996

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The first asymmetric Carroll rearrangement opens up an efficient access to highly functionalised ketones 4 and 7 with vicinal quaternary and tertiary stereogenic centres of excellent diastereo-and enantiomeric purity (de = 89-96%, ee = 82 to >98%) by using the SAMP/RAMP hydrazone methodology. Starting from hydrazones (S)-2, we describe a dianionic and a Lewis acid-mediated variant of the [3.3]-sigmatropic Carroll rearrangement. The relative and absolute configuration of the new stereogenic centres created by C-C bond formation were assigned by X-ray crystallographic analysis of the hydrazones 3h and 3j.The diastereo-and enantioselective generation of compounds bearing quaternary stereogenic centres as building blocks in natural product and drug synthesis is an attractive field in synthetic organic chemistry. In recent years many reports have been published concerning the creation of quaternary stereogenic centres" p71, although only a few allow the simultaneous preparation of adjacent stereogenic centresLsI. Intramolecular transformations such as sigmatropic rearrangements are highly suitable for this purpose, as for example the Ireland rearrangement, an important variation of the Claisen rearrangementL91. Due to the concerted, suprafacial nature of the Claisen rearrangement and the strong conformational preference for highly ordered chair-like transition states, in general products with high enantiomeric excesses are obtained. Asymmetric Ireland rearrangements with moderate to excellent asymmetric inductions have been described [lO]. The Carroll rearrangement ["] is such a tool, too. Although known since 1940, only a few diastereoselective[l2l or chirality transfer rearrangements ["] leading to optically active rearrangement products, have been described. Many different variations of the Carroll rearrangement are known, most of which proceed with decarboxylation of the initially formed p-ketoThe Carroll rearrangement has received much attention in the last few years due to the discovery of the dianionic variant[l5I. Recently, we have reported on the first asymmetric dianionic Carroll rearrangement and demonstrated in a short communication an efficient diastereo-and enantioselective synthesis of highly functionalised ketones [16]. In this paper we describe the asymmetric dianionic Carroll rearrangement in full detail and in addition a Lewis acid-mediated variant of the Carroll rearrangement. As depicted in Scheme 1, both types of rearrangements of hydrazono esters A lead to the highly functionalised products D although different diastereomers were obtained, due to the different transition states. While in the dianionic pathway dilithium or dialiminium P-hydrazono ester dienolates B undergo the rearrangement, in the Lewis acid-mediated pathway the ketene acetal C reacts.

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Struktur eines chiralen Lithium‐azaenolats: monomeres, intramolekular chelatisiertes Lithio‐2‐acetylnaphthalin‐SAMP‐hydrazon

Cited by 39 publications

References 15 publications

Molecular Structures of a Lithiated Schiff Base and a Related Dialkyl Ketone Imine

Molecular Structures of a Lithiated Schiff Base and a Related Dialkyl Ketone Imine

Structure and Reactivity of Lithium Enolates. From Pinacolone to Selective C‐Alkylations of Peptides. Difficulties and Opportunities Afforded by Complex Structures

The First Asymmetric Carroll Rearrangement Diastereo‐ and Enantioselective Synthesis of Polyfunctional Ketones with Vicinal Quaternary and Tertiary Stereogenic Centers

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