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The synthetic equivalents of the enantiopure binaphthyl bis(aryne) atropisomers derived from BINOL (1,1′‐bi‐2,2′‐naphtol) featuring a stereogenic axis vicinal to the two reactive triple bonds can be generated for the first time in solution in an enantiospecific manner. Using a two‐step sequence based on the bidirectional [4+2] cycloaddition of furan derivatives followed by an aromatizative deoxygenation reaction, several 9,9'‐bianthracenyl‐based atropisomers could be prepared enantiospecifically in high enantiomeric purity. Alternatively, bidirectional reactions with anthracene, 2‐bromostyrene, and perylene as the arynophiles afforded very congested bis(benzotriptycene), bis(tetraphene) and bis(anthra[1,2,3,4‐ghi]perylene) nanocarbon atropisomers in equally high enantiomeric purity. In complement, cross reactions with two different arynophiles revealed possible. The unusual atropisomer prototypes described in this study open the way to enantiopure nanographene atropisomers designed for functions. [ABSTRACT FROM AUTHOR]

One of the fundamental and intriguing aspects of life is the homochirality of the essential molecules. In this field, the absolute asymmetric synthesis of α-amino acids is a major challenge. Herein, we report access, by chemical means, to tertiary α-amino acid derivatives in up to 96 % ee without using any chiral reagent. In our strategy, the dynamic axial chirality of tertiary aromatic amides is frozen in a crystal and is responsible for the stereoselectivity of the subsequent steps. Furthermore, we could control the configuration of the final product by manually sorting and selecting the initial crystals. Based on vibrational circular dichroism studies, we could rationalize the observed stereoselectivity. [ABSTRACT FROM AUTHOR]

Organocopper reagents react with readily available chiral conjugated diene-ynes to give indene derivatives bearing two stereogenic centres. The investigation of this original reaction in optically pure series demonstrates that a double transfer of chirality is operating. A stereocontrolled cascade involving SN2' followed by carbocupration and conjugate addition reactions accounts for the total recovery of the initial chirality. The scope and limitations of the reaction were investigated. The high diastereofacial discrimination in the cyclisation step allowed the construction of the quaternary stereocentre with excellent dr and ee, with the opposite configuration depending on the E- or Z-configuration of the alkene in the starting material. Post-functionalisation of indenes allowed the synthesis of indanyl derivatives containing four contiguous stereocentres. [ABSTRACT FROM AUTHOR]

The title compound was obtained as a side product during dimerization-oxidation steps of the carbene generated from N-methylbenzothiazolium iodide. Chromatography on ( S, S)-Whelk O1 column showed on cooling a typical plateau shape chromatogram indicating an exchange between two enantiomers on the column. The thermal barrier to was determined (85 kJ.mol−1 at 10 °C) by dynamic high-performance (DHPLC).The absolute configuration of the first ( M) and second eluted ( P) enantiomers on the ( S, S)-Whelk O1 column was established by comparing the reconstructed circular dichroism (CD) spectra from the CD detector signal and the calculated CD spectrum of the ( P) enantiomer. revealed that 3,3'-dimethyl-3 H,3' H-2,2'-spirobi[[1,3]benzothiazole] can be viewed as a masked thiophenate attached to a benzothiazolium framework. Chirality 27:716-721, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

An original synthesis of chiral benzofulvenes triggered by organocopper reagents is reported. These enantiopure products are available through a highly chemo-, regio-, diastereo-, and enantioselective bis(alkylating) cycloisomerization process. A double chirality transfer (central-to-axial-to-central) is observed. [ABSTRACT FROM AUTHOR]

ABSTRACT The absolute configurations (AC) of azaheterocylic compounds resulting from the cascade of enediynes involving only light atoms were unambiguously assigned by the joint use of vibrational circular dichroism (VCD) and copper radiation single crystal X-ray diffraction (XRD). These AC determinations proved that the of enediynes proceeded with memory of chirality and of configuration. Chirality 25:832-839, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A noncatalysed nucleophilic aromatic substitution was used to prepare the (bacterio)chlorophyll mimics 2-Zn, 3-Zn, 4-Zn and 5-Zn. The localisation of the two recognition groups on the same side of the porphyrin macrocycles in 2-Zn, 4-Zn and 5-Zn produces, through metal-ligand interactions, oligomers that display both H- and J-type aggregates. These supramolecular architectures were confirmed by the introduction of optically pure atropisomers in 5-Zn, which produces chiral aggregates. The UV/Vis and electronic circular dichroism spectra of all aggregates are used to propose an excitonic splitting mode that would correspond to this dual type of chromophoric self-assembly. [ABSTRACT FROM AUTHOR]

The absolute configuration of the resolved axially chiral pyridine- N -oxide derivative, (±)- trans -2,6-di- ortho -tolyl-3,4,5-trimethylpyridine- N -oxide, has been determined by VCD and ECD analyses supported by TD-DFT calculations carried out at different levels of theory. DFT calculations confirmed that in spite of the two biaryl axes, the compound is conformationally less flexible and the major conformer is stabilized by two weak hydrogen bonds formed between the hydrogen of the methyl group of the tolyl moieties and the nitroxide oxygen. The experimental VCD spectra of this compound and the previously studied (±)-2,6-di-sec-butyl-4-methylpyridine-N-oxide with two stereogenic centers were compared in the frequency range 1200–1300 cm −1 . A (+,−,+)/(−,+,−) pattern of bands was observed in both cases. By replacing the sec -butyl moieties with tolyl ones, the VCD peaks shifted toward higher frequencies and the intensities were increased. [ABSTRACT FROM AUTHOR]

Abstract: Asymmetric allylic alkylation leading to dimethyl [(2E)-1,3-diphenylprop-2-en-1-yl]propanedioate 1 is a privileged reaction which has been considered in more than 800 references from 1985 to early 2012. This paper thus begins with a thorough review of the literature with a particular focus on the way the ee''s and absolute configuration of the prevailing enantiomer were claimed and reported by the authors. In a large majority of articles chiral chromatography is used for ee''s determination. Unfortunately, in too many cases the data, the column or the eluent are not provided. In a significant proportion (5%) the column name is ambiguous. Furthermore, several discrepancies are detected in the assigned order of elution when chiral chromatography data are provided. We therefore decided to firmly establish the chromatographic behavior of the enantiomers of 1, which were obtained from the corresponding racemate by semi-preparative chiral chromatography and their absolute configuration assigned by ECD and VCD spectroscopies. ORD curves show that optical rotation is very weak at 350nm with indication of inversion of the sign at lower wavelengths. It results in a low sensitivity for on line JASCO polarimeter detector. Chiroptical detection was nicely performed by on line JASCO CD detector set at 254nm: (−)-(S)-1 shows a (+)-CD254nm sign. Pure enantiomers of authenticated absolute configuration allowed a safe assignment of the order of elution during HPLC or SFC on major chiral stationary phases. Quite interestingly for practical application, the order of elution is reversed on Chiralpak AD-H and IA on going from hexane/EtOH to hexane/2-PrOH in HPLC or on going from CO2/EtOH (or MeOH) to CO2/2-PrOH in SFC. [Copyright &y& Elsevier]

Abstract: An inherently chiral ABii diphosphonato cavitand (±)-4 bearing a single quinoxaline bridging moiety was synthesized and resolved by chiral HPLC. Its chiroptical properties were investigated and VCD experiments allowed the determination of its absolute configuration. Distinguishable diastereomeric complexes in solution with l-adrenaline were observed by 1H and 31P NMR together with a noticeable enantio-discrimination at 253K (dr ∼2:1) in favor of the dextrorotatory cavitand (+)-4. [ABSTRACT FROM AUTHOR]

The atropenantiomers of stable 1,2,3,4-tetrahalo-1,3-butadiene derivatives (where halogeno stands for bromine or iodine) were separated with use of chiral HPLC. The barriers for the enantiomerization process were determined on-line by dynamic HPLC (DHPLC) or off-line by classical kinetic measurements. In the case of the tetrachloro compound, the barrier was too low for DHPLC and its value was obtained by dynamic NMR experiments. The obtained barriers for chloro, bromo, and iodo derivatives correlate with the van der Waals radii of the halogens. The absolute configuration of the isolated enantiomers of the tetraiodo and tetrabromo compounds was assigned by comparison of the experimental and conformations averaged calculated VCD spectra. The identification of a signature band of the absolute configuration of the butadiene core, the sign and location of which are independent from the different conformations and substituents, allowing the safe assignment of the absolute configuration of the enantiomers of chiral 1,3-butadienes, is also reported. [ABSTRACT FROM AUTHOR]