Electronic CD of Benzene and other Aromatic Chromophores for Determination of Absolute Configuration

Kurtán, Tibor; Antus, Sándor

doi:10.1002/9781118120392.ch3

Cited by 34 publications

(43 citation statements)

References 144 publications

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“…From the previous experience on the chiroptical properties of chiral aromatic compounds, it might be anticipated that the main determinant of the sign of the two major CD bands of 8aa was the configuration at the endocyclic chirality center, C‐2. When benzene ring is fused to a (partially) saturated heterocyclic ring, it is in fact the absolute conformation (ring helicity) adopted by this latter that dominates the chiroptical response . The same reasoning would apply to 1,2‐dihydroquinoline derivatives such as quinoline‐1(2 H )‐carboxylates with general structure 9 (Scheme ), provided that the R group attached at C‐2 does not contain chromophores absorbing above 220 nm.…”

Section: Resultsmentioning

confidence: 67%

Organocatalytic alkylation of carbohydrate‐containing aldehydes with dihydroquinoline N,O‐acetals: Absolute configuration of 1,2‐dihydroquinolines

et al. 2018

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The direct catalytic α‐amidoalkylation of dihydroquinolines with aldehydes bearing oxygen functionalities at different positions in a Mannich‐type reaction has been studied. β‐Alkoxy‐aldehyde 1d gave high enantioselectivity, albeit with an inherently poor diastereoselectivity, while the use of α‐alkoxy aldehydes 1c was detrimental also to enantioselectivity. Mannich‐type reactions have been studied for the first time using new chiral carbohydrate‐derived aldehydes 1a,b showing a reactivity markedly influenced by the presence of water. The chiral glycidic backbone showed a slight but significant influence on the overall stereochemical outcome only when present in α‐position of the aldehyde. The absolute stereochemistry of the products was studied by electronic circular dichroism (ECD) spectra and compared with theoretical calculations. ECD analysis easily provides the absolute configuration of 1,2‐dihydroquinoline derivatives such as quinoline‐1(2H)‐carboxylates.

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Section: Resultsmentioning

confidence: 67%

Organocatalytic alkylation of carbohydrate‐containing aldehydes with dihydroquinoline N,O‐acetals: Absolute configuration of 1,2‐dihydroquinolines

et al. 2018

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“…Negative ω C‐5a,C‐4,C‐3,O torsional angle implies M helicity of the heteroring, which results in negative n − π* CE regardless of the substitution pattern of the aromatic ring. This helicity rule was established on the basis of synthetic 3‐substituted dihydroisocoumarin derivatives and it was confirmed by TDDFT ECD calculations and applied to the configurational assignment of natural dihydroisocoumarins . According to this helicity rule, the negative n − π* CE of the second‐eluted enantiomer at 271 nm derives from M helicity of the heteroring.…”

Section: Resultsmentioning

confidence: 69%

O‐Heterocyclic Embeurekols from Embellisia eureka, an Endophyte of Cladanthus arabicus

et al. 2013

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Three new polyketides ((-)-1, (+)-1, and 2) were isolated from the EtOAc extract of the fungus Embellisia eureka, an endophyte of the Moroccan plant Cladanthus arabicus (Asteraceae). The structures of these new compounds were determined on the basis of one- and two-dimensional NMR spectroscopy as well as by high-resolution mass spectrometry. The absolute configurations of (-)-1, (+)-1, and 2 were determined by TDDFT ECD calculations of solution conformers, online HPLC-ECD analysis, and the modified Mosher method.

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“…According to these rules the sign of the CE allied to the n‐π* transition can be directly related to the ring helicity of the major conformer and therefore to the compound AC. Some more recent studies, however, have clearly shown that such qualitative AC assignment, based only on n‐π* band inspection, is essentially unreliable, because both aromatic substitution and complex conformer populations strongly influence the sign of naphthalenone carbonyl CE …”

Section: Resultsmentioning

confidence: 99%

Computational ECD Spectrum Simulation of the Phytotoxin Scytalone: Importance of Solvent Effects on Conformer Populations

Mazzeo

Cimmino²,

Andolfi³

et al. 2014

Chirality

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A time-dependent Density Functional Theory (TDDFT) computational simulation of the electronic circular dichroism (ECD) spectrum of the phytotoxin scytalone (1), produced by different plant pathogenic fungi and involved in melanin production, was undertaken with the aim to establish a nonempirical correlation between the spectrum and the absolute configuration of this compound. In fact, very low optical rotation data of do not afford a reliable absolute configuration assignment while, on the contrary, the use of ECD can provide a useful tool for its stereochemical description. This structurally simple molecule displayed a considerable molecular flexibility, which made it mandatory to obtain an accurate conformers distribution to get a good reproduction of the experimental ECD spectrum. Only the application of an implicit integral equation formalism Polarizable Continuum Model (IEF-PCM) solvation model in the calculations allowed us to properly describe the conformer populations and finally obtain a more than satisfactory spectral simulation.

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Electronic CD of Benzene and other Aromatic Chromophores for Determination of Absolute Configuration

Cited by 34 publications

References 144 publications

Organocatalytic alkylation of carbohydrate‐containing aldehydes with dihydroquinoline N,O‐acetals: Absolute configuration of 1,2‐dihydroquinolines

Organocatalytic alkylation of carbohydrate‐containing aldehydes with dihydroquinoline N,O‐acetals: Absolute configuration of 1,2‐dihydroquinolines

O‐Heterocyclic Embeurekols from Embellisia eureka, an Endophyte of Cladanthus arabicus

Computational ECD Spectrum Simulation of the Phytotoxin Scytalone: Importance of Solvent Effects on Conformer Populations

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