Synthese und Struktur eines hochsubstituierten Tetracyclo[3.3.0.0
            <sup>2,8</sup>
            .0
            <sup>4,6</sup>
            ]octans (Nortriasteran)

Quast, Helmut; Christ, Josef; Peters, E.‐M.; Peters, Karl

doi:10.1002/cber.19851180333

Cited by 8 publications

(2 citation statements)

References 41 publications

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“…Newman projec-C2/C4 and C4/C6 of this state is certainly larger than that tions along the bonds between the ipso carbon atoms of the phenyl groups and the carbon atoms C8 (left) and C4 (right) for (1S)-1 of a localised valence tautomer, the occupation of such (middle) and the racemate rac-1 (below) [4] higher, vibronic states is one of the reasons for the large values of this sum measured by X-ray diffraction analyses [26] and semibullvalcyclic skeleton of the racemic (rac-1) [4] and the nonracemic barba-enes. [2,7,32] In the absence of precise knowledge of the proralanedicarbonitrile (1S)-1 and differences between the distances portions and the geometry of the higher states, however,…”

Section: X-ray Diffraction Analyses Of the Bicyclic Ketones Rac-endo-mentioning

confidence: 99%

“…Degenerate Cope rearrangements via transition considered as the transition state of the degenerate Cope states of C S symmetry lead to enantiomerisation, of co-rearrangement 1 o 1Ј and may be represented by the bishourse. [2] No nonracemic degenerate barbaralane or semi-moaromatic C 2 structure 1*. [5] This simple model applies bullvalene has yet been prepared.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile – Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement

Quast¹,

Seefelder

Peters

et al. 1999

Eur. J. Org. Chem.

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Diphenylbicyclo[3.3.1]nonane‐2,6‐dione rac‐3 is resolved in 57 % overall yield by chromatographic separation of the diastereomeric (R)‐N‐(1‐phenylethyl)carbamates 9 which are obtained from (R)‐(1‐phenylethyl) isocyanate (8) and the 6‐hydroxydiphenylbicyclo[3.3.1]nonan‐2‐ones endo‐ and exo‐4. The enantiomers (1R)‐ (e.r. = 98:2) and (1S)‐3 (e.r. = 97:3) are regenerated from 9 by reduction with lithium aluminium hydride followed by Swern oxidation of the resulting diols 5. The title compound (1S)‐1 is synthesised in three steps from (1S)‐3 in improved yield on the route that had led to rac‐1. The absolute configurations are established by X‐ray diffraction analyses of the carbamates endo‐(1R)‐9 and exo‐(1S)‐9. X‐ray diffraction analyses were also performed of the camphanoate (1R)‐7, the intermediates rac‐endo‐4 and (1S)‐3, and the title compound (1S)‐1. Hydroxy ketone rac‐endo‐4 adopts similar conformations in the solid state and in solution as shown by a comparison of vicinal 1H,1H coupling constants from proton spectra with those calculated from torsional angles in the crystal. The molecular structures of (1S)‐1 and (1S)‐3 closely resemble those of the corresponding racemates investigated previously. These results show (i) that intermolecular interactions in the solid state are of minor importance and (ii) that the unusually long C2–C8 distance of (1S)‐1 and rac‐1 (168 pm) is a molecular but not an averaged property due to a non‐degenerate Cope rearrangement in the crystal. CD spectra are reported for (1R)‐ and (1S)‐3, the unsaturated dicarbonitrile (1S)‐13, and (1S)‐1. The CD spectrum of (1S)‐1 exhibits a weak positive band at 459 nm where rac‐1 shows a temperature‐dependent absorption which has been assigned to the higher, vibronic state represented by rac‐1*. The intensity of the weak CD band depends on the temperature and the solvents in the same way as the UV/Vis absorption of rac‐1. This supports the conclusion that both bands originate from the same source, viz. the transition state 1* of the degenerate Cope rearrangement 1 ⇄ 1′.

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Section: X-ray Diffraction Analyses Of the Bicyclic Ketones Rac-endo-mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile – Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement

Quast¹,

Seefelder

Peters

et al. 1999

Eur. J. Org. Chem.

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Synthese, Struktur und thermische Umlagerungen des 2,6‐Dicyan‐1,5‐dimethylsemibullvalens

et al. 1985

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Zinkiodid-katalysierte Addition von Trimethylsilylcyanid an dasThe zinc iodide-catalyzed addition of trimethylsilyl cyanide to the bicyclo[3.3 .O]octane-2,6-dione 9 yields the sterically defined 0-silylated cyanohydrine 10. Trichlorophosphane oxide in pyridine converts the latter to the unsaturated dinitrile 11. Bromination of 11 using N-bromosuccinimide affords the exo,exo-dibromodinitrile 13. The latter is debrominated by zinc/copper to the dicyanosemibullvalene 4a while the dehydrobromination with potassium tert-butoxide in tert-butyl alcohol yields the bromodicyanosemibullvalene 14. All reactions proceed smoothly giving high yields. Using 14, which exists as a single valence tautomer, as a model of a non-rearranging valence tautomer of 4 a the barrier for the degenerate Cope rearrangement of 4a is estimated from the broadening of the 13C NMR signals to be A G & = 13 kJ mol-'. At 130°C in [D,]benzene, 4a isomerizes to the cyclooctatetraene 16 with a first order rate constant of k = 3.0 s-'.The semibullvalene 4a crystallizes monoclinically in the space group P 2 , / n (No. 14) with four molecules in the unit cell. Selected geometric parameters of 4a are compared to those of cyanosubstituted cyclopropane derivatives and other semibullvalenes.

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2,6‐Dimethyl Semibullvalene‐2,6‐dicarboxylates

et al. 1992

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The enolized p-0x0 ester 9 is reduced by NaB(CN)H, in weakly acidic methanol solution to afford an almost quantitative yield of a mixture of diastereomeric P-hydroxy esters 10. On treatment with phosphorus oxychloride in pyridine, 10 is converted into a mixture of the P-chloro esters exo-11, endo-11, exo-12, endo-12, and 13 which is separated in part by chromatography. Sodium methoxide in methanol eliminates hydrogen chloride from the crude mixture of P-chloro esters producing the a$-unsaturated ester ?a in 84% yield based on 9. -Acid-catalysed equilibration of the known vinyl sulphides C2-and Cs-15 is carried out on large scale furnishing a 7 3~2 7 ratio of C2-and Cs-15. This mixture is oxidized to the sulphones C2-and Cs-16 which are allowed to react with sodium cyanide supported on aluminium oxide affording the u,punsaturated dinitrile 17 which is isolated by chromatography. Thus, 17 is now available on a 30-g scale. Methanolysis of l?by a prolonged treatment with hydrogen chloride in methanol followed by hydrolysis of the Pinner salt leads to ?b. -Both a$-unsaturated esters 7 a and b are readily brominated at the allylic positions by N-bromosuccinimide to yield the y,y'-dibromo esters 19a and b. Zinc-copper couple in tetrahydrofuran converts 19a and b into the semibullvalenedicarboxylates 2 a and b. While 2 a is persistent only in dilute solutions, thus frustrating all attempts at its isolation, 2b exhibits considerable stability in solution and forms lemon-coloured crystals.The semibullvalenedicarboxylates 2 a and b undergo a very rapid degenerate Cope rearrangement in solution. In addition, 2 b exhibits reversible thermochromism in both solution and solid state. The structures of the new compounds are based on spectroscopic evidence, including mass, IR, and NMR spectra. The configurations of exo-11, exo-l2,19a and bare established by X-ray diffraction analyses.The predicted accelerating effect of n-acceptor substituents on the degenerate Cope rearrangement of bridged homotropilidenes, e.g. bullvalenes, barbaralanes, and semibullvalenes[21, was demonstrated for the first time in the barbaralane series, with 2,6-dicyanobarbaralane as the andi id ate^^,^]. Shortly afterwards, the 2,6-dicyanosemibullvalene 1 b has been which not only corroborated this resultr6] but also stimulated new interest by exhibiting exceptional properties, such as being yellow in the absence of a chromophor, showing reversible thermochromism ['], and, in the solid state, a rapid non-degenerate Cope rearrangement between valence tautomers non-equivalent only by virtue of their environment in the crystal lattice"'. The interesting colour and thermochromism of 1 b are shared by the 1,5-bridged semibullvalene-2,6-dicarbonitrile 1 c[lo,lll but not by the 3,7-dicyanosemibullvalene 4a['2-141 nor the corresponding dimethyl 3,7-dicarboxylate 4 b"2,151. Grohmann's series of tetramethyl semibullvalenetetracarboxylates 3 seems to exhibit properties similar to those of the dinitriles 1. Unfortunately, an investigation of the thermochromism of 3 is s...

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Synthese und Struktur eines hochsubstituierten Tetracyclo[3.3.0.0 ^2,8 .0 ^4,6 ]octans (Nortriasteran)

Cited by 8 publications

References 41 publications

Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile – Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement

Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile – Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement

Synthese, Struktur und thermische Umlagerungen des 2,6‐Dicyan‐1,5‐dimethylsemibullvalens

2,6‐Dimethyl Semibullvalene‐2,6‐dicarboxylates

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Synthese und Struktur eines hochsubstituierten Tetracyclo[3.3.0.0 2,8 .0 4,6 ]octans (Nortriasteran)

Cited by 8 publications

References 41 publications

Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile – Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement

Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile – Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement

Synthese, Struktur und thermische Umlagerungen des 2,6‐Dicyan‐1,5‐dimethylsemibullvalens

2,6‐Dimethyl Semibullvalene‐2,6‐dicarboxylates

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Synthese und Struktur eines hochsubstituierten Tetracyclo[3.3.0.0 ^2,8 .0 ^4,6 ]octans (Nortriasteran)