Stereoisomerisierungen von Keteniminen

Lambrecht, J.; Gambke, Brigitte; Seyerl, J. Von; Hüttner, Gottfried; Nell, Georg Kollmannsberger‐von; Herzberger, Siegfried; Jochims, Johannes C.

doi:10.1002/cber.19811141203

Cited by 36 publications

(20 citation statements)

References 24 publications

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“…Dynamic NMR studies and MO calculations of acyclic ketene imines suggest enantiomerization by N-inversion, rather than rotation about the CCN axis [15] [16], an outcome in accordance with topomerization studies of ketimines [17]. Barriers of 14 ± 15 kcal mol À1 were measured for trialkylketene imines; they are substantially reduced by aryl or electron-attracting substituents at the C-atom.…”

Section: 2supporting

confidence: 69%

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Huisgen

Mlostoń

Langhals

et al. 2002

HCA

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Dedicated to George A. Olah on the occasion of his 75th birthday When −thiocarbonyl ylide× 1A ( (2,2,4,4-tetramethyl-3-oxocyclobutylidenesulfonio)methanide) is generated from the dihydrothiadiazole 5A by N 2 extrusion at 408 in the presence of 2,3-bis(trifluoromethyl)fumaronitrile ((E)-10), a cyclic seven-membered ketene imine 11 and trans-thiolane 12 are formed (81 : 19). The reaction of 1A with (Z)-10 furnishes 11, 12, and cis-thiolane 25 in the ratio of 82 : 12 : 6. The strained ketene imine 11 is crystalline and storable as a consequence of the stabilizing −perfluoroalkyl effect×. The ketene imine group is stereogenic; 11 has a transoid structure with respect to the CF 3 groups, and there is no evidence for the cisoid diastereoisomer. Ketene imine 11 adds H 2 O, MeOH, and PhNH 2 . In solution at 608, 11 undergoes an irreversible ring contraction, furnishing the thiolanes 12/25 98 : 2. The rate constant of this first-order rearrangement increases 850-fold, as the solvent polarity rises from cyclohexane to CD 3 CN, in accordance with a zwitterionic intermediate. It is the same intermediate that is initially formed from 1A and 10, and its intramolecular N-and C-alkylation give rise to 11 and 12 25, respectively. In contrast to 1A, thiocarbonyl ylide 27, which harbors the sterically less-demanding adamantylidene group, reacts with (E)-10 to give trans-thiolane 29, but no ketene imine. The precursor 26 catalyzes the (Z)/(E) isomerization of 10 ((E)/(Z) ca. 95 : 5 at equilibrium), thus obviating conclusions on steric course and mechanism of this cycloaddition.

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Section: 2supporting

confidence: 69%

Untitled

Huisgen

Mlostoń

Langhals

et al. 2002

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“…3); on the other hand, two further resonance structures, one of those analogous to the polar resonance form II, contribute significantly to the ground state of simple ketene imines of type 1 [43]. Theoretical studies and crystal structure analyses of those ketene imines [44] [45] further support the contribution of the structure II, showing an increase of the CN bond order depending on the substituents.…”

Section: Methodsmentioning

confidence: 62%

Desulfurization of 4-Nitro-N,2-diphenyl-3-(phenylamino)isothiazol- 5(2H)-imine: Formation of a 3-Imino-2-nitroprop-2-enamidine

Argilagos

Kunz

Linden

et al. 1998

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“…Accordingly, compound 3 shows an absorption peak at 2240 cm -1 , which shifts to 2080 cm -1 upon going to 4. Thus, the nitrile absorption band of the anion appears close to the absorption band of neutral ketene-imines R 2 C=C=NR (1995-2040 cm -1 ) [20].…”

Section: Discussionmentioning

confidence: 97%

Supramolecular structure of the tetrabutylammonium salt of 2-phenylpropionitrile

Reetz¹,

Hütte

Goddard

1999

J. prakt. Chem.

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The term "carbanion" has been applied by synthetic organic chemists for decades to denote carbon-based anionic species [1]. In doing so, structural aspects are knowingly ignored. The basis of traditional and modern carbanion chemistry is formed by the many different types of organolithium reagents, including alkyllithium compounds, lithiated heterocycles, and deprotonated forms of carbonyl compounds (enolates), nitriles, nitroalkanes, sulfoxides, sulfones, and other CHacidic precursors [1,2]. In addition to purely synthetic aspects, considerable effort has gone into the study of the structural properties of these reagents [3]. Indeed, it has long been accepted that carbanions are not involved at all; rather, lithium is intimately bonded to the nucleophilic species which occur as monomers, dimers or higher aggregates.In contrast to these and other organometallic reagents, the scientific community took a different view of metal-free anionic systems. Specifically, the tetraalkylammonium salts of CH-acidic compounds such as esters, ketones, nitriles, nitroalkanes, and sulfones were believed to be naked anions and therefore true carbanions However, detailed structural studies in the solid phase and in solution of compounds of the type 2 showed that the concept of naked anions does not apply at all [11]. Indeed, these and other tetraalkylammonium salts of CH-acidic compounds, e.g., those of 2-nitropropane [12], phenylacetic acid ester [13] or phenylpropionic acid ester [13], are not true carbanions. The tetrabutylammonium units are not isolated cations, but are in fact intimately associated with the carbon nucleophiles. This novel phenomenon is based on strong hydrogen bonds originating from the α-methylene units of the tetrabutylammonium cations as H-donors and the negatively charged oxygen atoms in the enolates 2 (or in nitronates) as H-acceptors (CH···O interactions) [14]. Relevant are MO calculations on (CH 3 ) 4 N + , which show that the positive charge is not localized on nitrogen as traditionally drawn by organic chemists, but delocalized evenly over the four methyl groups [9]. This also means that the methyl groups (or α-methylene groups in R 4 N + ) are somewhat acidic. Interestingly, in the case of enolates 2 eight of the CH···O interactions occur in such a way that a dimer-

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Stereoisomerisierungen von Keteniminen

Cited by 36 publications

References 24 publications

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Desulfurization of 4-Nitro-N,2-diphenyl-3-(phenylamino)isothiazol- 5(2H)-imine: Formation of a 3-Imino-2-nitroprop-2-enamidine

Supramolecular structure of the tetrabutylammonium salt of 2-phenylpropionitrile

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