Das erste enantiomerenreine Triangulan: (M)-Trispiro[2.0.0.2.1.1]nonan ist ein σ-[4]Helicen

Meijere, Armin de; Хлебников, А. Ф.; Kostikov, R. R.; Kozhushkov, Sergei I.; Schreiner, Peter R.; Wittkopp, Alexander; Yufit, D. S.

doi:10.1002/(sici)1521-3757(19991203)111:23<3682::aid-ange3682>3.0.co;2-x

Cited by 43 publications

(34 citation statements)

References 30 publications

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“…Among them, the linear triangulanes with more than three spiro-linked cyclopropane units display an interesting stereochemical phenomenon in that they are chiral, but with stereogenic centers that have four different alkyl substituents only [6]. This stimulated us to prepare the first [n]triangulanes in enantiomerically pure form and investigate their properties (Scheme 1) [7,8].…”

Section: The First Enantiometrically Pure [N]triangulanesmentioning

confidence: 99%

“…2. Scheme 1 First synthesis of enantiomerically pure (M)-(-)- [4]triangulane and a comparison of its measured and DFT/SCI-computed specific rotations [7]. (a) BF 3 ؒEt 2 O, EtOH, 78 °C, 2 h; (b) CH 2 I 2 , Zn, DME, ultrasound, 80°C, 2 h; (c) LiAlH 4 A line connecting the methylene groups of the inner spiropentane moieties with one each of the outer rings resembles a mechanical model of the helicity of [4]-, [5]-, and [6]triangulane.…”

Section: The First Enantiometrically Pure [N]triangulanesmentioning

confidence: 99%

“…While the molecular structures were-of course-identical, the crystal packing for the enantiomerically pure and the racemic compound were found to be significantly different [8]. Although the enantiomeric purity for the (M)-enantiomer was of the same order as that for the (P)-enantiomer, the specific rotation was about 11 % [7,8].…”

Section: The First Enantiometrically Pure [N]triangulanesmentioning

confidence: 99%

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New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

et al. 2003

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The structurally intriguing [4]-and [5]triangulanes have been prepared in enantiomerically pure form. Their surprisingly high specific rotations are well reproduced by DFT/SCI computations and stem from the fact that these hydrocarbons essentially are σ-helicenes (i.e., rigidly held helical arrangements of σ-bonds). Some light is shed on the properties of radical cations derived from [3]-and [4]rotanes. While the former adopts C s or C 2v symmetry, the latter retains the D 4h symmetry of the neutral hydrocarbon, according to highlevel computations. Experimental and computational evidence is also presented that the antiaromatic cyclopentadienyl cation is stabilized as a singlet ground state by five cyclopropyl substituents. Yet, the three cyclopropyl groups in tricyclopropylamine do not favor the formation of its radical cation, because they are not in the proper orientation. When this amine radical cation is generated by cobalt γ-irradiation in a Freon matrix, evidence for a significant conformational change is obtained by EPR spectroscopy. Finally, the conformational dynamics of the newly prepared crowded molecules tetracyclopropyl-and tetraisopropylmethane are discussed.

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Section: The First Enantiometrically Pure [N]triangulanesmentioning

confidence: 99%

Section: The First Enantiometrically Pure [N]triangulanesmentioning

confidence: 99%

Section: The First Enantiometrically Pure [N]triangulanesmentioning

confidence: 99%

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New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

et al. 2003

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“…6 with an explanation of the details of the graphical representation given in the following section. One sees that the motion of the H-atoms, though not identical for the two pairs, is quite similar, essentially a twisting motion, with a more substantial rocking content for the pair (13,14) at lower frequency. Most of the distinction between the two pairs of vibrations comes about by the Hatoms of the two CH 2 groups of the outer rings moving out-of-phase in the lowerfrequency pair, and in-phase in the higher-frequency pair.…”

mentioning

confidence: 91%

“…In spite of inherent helicity no longer presenting the obstacle to the computation of ROA and VCD that it did a decade ago, no theoretical work on this unique vibrational model chromophore has so far been published. The recent synthesis of enantiomerically pure (À)-(M)-s- [4]helicene [13] has provided the incentive for a theoretical study of the molecule. Moreover, a newly developed Raman optical-activity spectrometer [14] made it possible to measure the vibrational optical activity with a far higher precision than before achieved.…”

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confidence: 99%

Raman Optical Activity of a Purelyσ-Bonded Helical Chromophore: (−)-(M)-σ-[4]Helicene

Hug

Zuber

Meijere

et al. 2001

HCA

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The recent synthesis of enantiomerically pure (À)-(M)-s- [4]helicene has provided an archetype helical model system for vibrational optical activity, comparable to what p-helicenes represent in the field of electronic optical activity. We present the first measurements and the first calculations of the Raman optical activity (ROA) of this interesting molecule. Observed and calculated ROA is large throughout the vibrational spectrum, in agreement with expectations, and spectacular effects, with D values close to 0.5%, occur in the 900-cm À1 region. Agreement between the experimental spectrum and the theoretical one, calculated with densityfunctional theory for the vibrational part and Hartree-Fock linear response theory for the molecular electronic tensors, is excellent, clearly the best that has been achieved to date in the field. This allows us to place confidence in the results of an analysis of Raman and ROA scattering generation in the molecule, obtained by a newly developed graphical procedure for extracting this kind of information from ab initio calculations. One finds that relative contributions made by carbon and hydrogen atoms can be comparable in size, but can also vary considerably, even between closely lying vibrations, and that, for most vibrations, the generation of ROA difference intensity is distributed rather differently than that of Raman intensity over the shape of the molecule. The sign of the ROA is, for the set of vibrations in the 900-cm À1 region, which we analyze in detail, determined by coupling terms between the two halves of the molecule, while Raman intensity is primarily generated within the two fragments, with coupling terms between them only adding to or substracting from it.Introduction. ± The molecules chosen as model systems in the first successful observations of Raman optical activity (ROA) and vibrational circular dichroism (VCD) of molecular origin owed their chirality to the presence of a stereogenic C-atom carrying four different substituents [1] [2]. The rigid frame of bicyclic terpenes was soon included in the list of model chromophores in vibrational optical activity [3] [4]. Both systems also served as vehicles for the first successful recording of entire vibrational optical-activity spectra [5]. It subsequently became clear that the three-dimensional rigid structure of bicyclic compounds not only provided the benefit of the absence of conformational mobility, but also tended to yield sizable chiroptical effects throughout the vibrational spectrum. Bicyclic terpenes, a-pinene in particular, have become standard compounds for calibrating ROA and VCD spectrometers, and for comparing their performance [6] [7].A plethora of other kinds of molecules, considered suitable as model compounds for vibrational optical activity for one reason or another, has since been investigated.

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R aman Optical Activity Spectroscopy

Hug

2001

Handbook of Vibrational Spectroscopy

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Das erste enantiomerenreine Triangulan: (M)-Trispiro[2.0.0.2.1.1]nonan ist ein σ-[4]Helicen

Cited by 43 publications

References 30 publications

New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

Raman Optical Activity of a Purelyσ-Bonded Helical Chromophore: (−)-(M)-σ-[4]Helicene

R aman Optical Activity Spectroscopy

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