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The reactivity of novel chiral lactamide‐substituted diselenide‐based reagents under oxidative conditions was exploited to develop a metal‐free method for the preparation of enantioenriched allenylamides from simple alkynes in good yields, and with enantiomeric excesses up to 99 %. The key of the success in this method is attributed to the hydrogen‐bonded lactamide appendages that ensure configurational stability of chiral vinyl selenoxide intermediates for an optimal enantiotopic β‐syn‐elimination step. [ABSTRACT FROM AUTHOR]

Isocaloteysmannic acid (1), a new chromanone, was isolated from the leaf extract of the medicinal species Calophyllum tacamahaca Willd. along with 13 known metabolites belonging to the families of biflavonoids (2), xanthones (3–5, 10), coumarins (6–8) and triterpenes (9, 11–14). The structure of the new compound was characterized based on nuclear magnetic resonance (NMR), high-resolution electrospray mass spectrometry (HRESIMS), ultraviolet (UV) and infrared (IR) data. Its absolute configuration was assigned through electronic circular dichroism (ECD) measurements. Compound (1) showed a moderate cytotoxicity against HepG2 and HT29 cell lines, with IC50 values of 19.65 and 25.68 µg/mL, respectively, according to the Red Dye method. Compounds 7, 8 and 10–13 exhibited a potent cytotoxic activity, with IC50 values ranging from 2.44 to 15.38 µg/mL, against one or both cell lines. A feature-based molecular networking (FBMN) approach led to the detection of a large amount of xanthones in the leaves extract, and particularly analogues of the cytotoxic isolated xanthone pyranojacareubin (10). [ABSTRACT FROM AUTHOR]

An access to functionalised eight‐membered carbocyclic ring compounds was developed by simply stirring an unusual vinylogous Donor‐Acceptor Cyclopropane (DAC) in boiling o‐xylene. Both experimental and computational studies were performed to explain the diastereoselectivity/regioselectivity transfer observed and to provide an overall picture of the mechanism. [ABSTRACT FROM AUTHOR]

We report here the development of a rotating molecular switch based on metal‐catalyzed reversible (de)‐hydrogenation. Under an argon atmosphere, acceptorless dehydrogenation induces a switch from an alcohol to a ketone, while reversing to a hydrogen pressure switches back the system to the alcohol. Based on a tolane scaffold, such reversible (de)‐hydrogenation enables 180° rotation. The absence of waste accumulation in a switch relying on chemical stimuli is of great significance and could potentially be applied to the design of efficient complex molecular machines. [ABSTRACT FROM AUTHOR]

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]

The racemization mechanism of tert‐butylphenylphosphido‐borane is investigated experimentally and theoretically. Based on this converging approach, it is shown, first, that several phosphido‐borane molecular species coexist at the time of the reaction and, second, that one particular of both initially assumed reactive routes most significantly contribute to the overall racemization process. From our converging modeling and experimental measurement, it comes out that the most probable species to be here encountered is a phosphido‐borane‐Li (THF)2 neutral solvate, whose P‐stereogenic center monomolecular inversion through a Y‐shaped transition structure (ΔrG°≠: 81 kJ mol−1) brings the largest contribution to the racemization process. [ABSTRACT FROM AUTHOR]

Chiral zirconium(IV) double cage sandwich complex Zr(1)2 has been synthesized in one step from porphyrin cage H21. Zr(1)2 was obtained as a racemate, which was resolved by HPLC and the enantiomers were isolated in >99.5% ee. Their absolute configurations were assigned on the basis of X-ray crystallography and circular dichroism spectroscopy. Vibrational circular dichroism (VCD) experiments on the enantiomers of Zr(1)2 revealed that the chirality around the zirconium center is propagated throughout the whole cage structure. The axial conformational chirality of the double cage complex displayed a VCD fingerprint similar to the one observed previously for a related chiral cage compound with planar and point chirality. Zr(1)2 shows fluorescence, which is quenched when viologen guests bind in its cavities. The binding of viologen and dihydroxybenzene derivatives in the two cavities of Zr(1)2 occurs with negative allostery, the cooperativity factors α (= 4 K2/K') being as low as 0.0076 for the binding of N,N'-dimethylviologen. These allosteric effects are attributed to a pinching of the second cavity as a result of guest binding in the first cavity. [ABSTRACT FROM AUTHOR]

We report a molecular design and concept using π‐system elongation and steric effects from helicenes surrounding a triphenylene core toward stable chiral polycyclic aromatic hydrocarbons (PAHs) with a maximal π‐distortion to tackle their aromaticity, supramolecular and molecular properties. The selective syntheses, and the structural, conformational and chiroptical properties of two diastereomeric large multi‐helicenes of formula C90H48 having a triphenylene core and embedding three [5]helicene units on their inner edges and three [7]helicene units at their periphery are reported based on diastereoselective and, when applicable, enantiospecific Yamamoto‐type cyclotrimerizations of racemic or enantiopure 9,10‐dibromo[7]helicene. Both molecules have an extremely distorted triphenylene core, and one of them exhibits the largest torsion angle recorded so far for a benzene ring (twist=36.9°). [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]

The chirality issues in the essential oils (EOs) of leaves and flowers from Bubonium graveolens were addressed by chiral high-performance liquid chromatography (HPLC) with polarimetric detection and vibrational circular dichroism (VCD). The chemical compositions of the crude oils of three samples were established by gas chromatography / mass spectrometry (GC/MS). The well-known cis-chrysanthenyl acetate ( 1), oxocyclonerolidol ( 2), and the recently disclosed cis-acetyloxychrysanthenyl acetate ( 3), the three major chiral compounds, were isolated by preparative HPLC. The naturally occurring oxocycloneroledol ( 2), mostly found in the leaf oil (49.4-55.6%), presents a (+) sign in the mobile phase during HPLC on a chiral stationary phase (CSP) with a Jasco polarimetric detection. The naturally occurring cis-chrysanthenyl acetate ( 1) and cis-acetyloxychrysanthenyl acetate ( 3), mostly found in the flower EO (35.9-74.9% and 10.0-34.3%, respectively), both present a (−) sign. HPLC on a CSP with polarimetric detection is an unprecedented approach to readily differentiate the flower and leaf EOs according to their chiral signature. The comparison of the experimental and calculated VCD spectra of pure isolated 1, 2, and 3 provided their absolute configuration as being (1 S,5 R,6 S)-(−)-2,7,7-trimethylbicyclo[3.1.1]hept-2-en-6-yl acetate 1, (2 R,6 R)-(+)-6-ethenyl-2,6-dimethyl-2-(4-methylpent-3-en-1-yl)dihydro-2H-pyran-3(4H)-one) 2 and (1 S,5 R,6 R,7 S)-(−)-7-(acetyloxy)-2,6-dimethylbicyclo[3.1.1]hept-2-en-6-yl]methyl acetate 3. Compounds 1, 2, and 3 were already known in B. graveolens but this is the first report of the absolute configuration of (+)- 2 and (−)- 3. The VCD chiral signatures of the crude oils were also recorded. [ABSTRACT FROM AUTHOR]

The combination of aminocatalysis with N-heterocyclic carbene catalysis has been extended to a switchable dual catalytic system, which allowed a direct enantioselective entry to bridged bicyclo[3.n.1] ring systems and the total synthesis of the natural product (1R)-suberosanone. [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]

Access to hydroxy-functionalized P-chiral phosphine-boranes has become an important field in the synthesis of P-stereogenic compounds used as ligands in asymmetric catalysis. A family of optically pure α and β-hydroxyalkyl tertiary phosphine-boranes has been prepared by using a three-step procedure from readily accessible enantiopure adamantylphosphinate, obtained by semi-preparative HPLC on multigram scale. Firstly, a two-step one-pot transformation affords the enantiopure hydroxyalkyl tertiary phosphine oxides in good yields and enantioselectivities. The third step, BH3-mediated reduction, allows the formation of the desired phosphine-boranes with excellent stereospecifity. The mechanistic study of this reduction provides new evidence to elucidate the crucial role of the pendant hydroxy group and the subsequent activation of the PO bond by the boron atom. [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]

The organocatalytic enantioselective conjugate addition of secondary β-ketoamides to α,β-unsaturated carbonyl compounds is reported. Use of bifunctional Takemoto's thiourea catalyst allows enantiocontrol of the reaction leading either to simple Michael adducts or spirocyclic aminals in up to 99 % ee. The origin of the enantioselectivity has been rationalised based on combined DFT calculations and kinetic analysis. This study provides a deeper understanding of the reaction mechanism, which involves a predominant role of the secondary amide proton, and clarifies the complex interactions occurring between substrates and the catalyst. [ABSTRACT FROM AUTHOR]

Enantiopure (±)-2,6-di-sec-butyl-4-methylpyridine and its oxidized form (±)-2,6-di-sec-butyl-4-methylpyridine-N-oxide were prepared and then separated by chiral HPLC. Their stereochemical structures and their conformational distribution in solution were investigated using vibrational circular dichroism (VCD) and infrared spectroscopy (IR) combined with density functional theory (DFT). The experimental spectra have been compared with theoretical data. This comparison indicated that (−)-2,6-di-sec-butyl-4-methylpyridine and its oxidized form (+)-2,6-di-sec-butyl-4-methylpyridine-N-oxide have an (S,S)-configuration and exist in several conformations. The good fit confirms the reliability of the conformational analysis. Our results indicated that going from the reduced form to the oxidized one strongly influences the type of conformers in solution. Moreover, DFT calculations showed that for all of the conformers of (S,S)-2,6-di-sec-butyl-4-methylpyridine-N-oxide, the formation of four centered intramolecular hydrogen bonds between the hydrogen of the –CH, –CH2, and –CH3 groups and the nitroxide oxygen is possible. Moreover the stability of the conformers of both compounds is influenced by the all-trans structure of the sec-butyl moieties. [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]

During a program dedicated to the biocatalytic access of structurally useful α-hydroxy ketones, we made the unexpected observation that epoxy enol acetates derived from (+)- and (-)-menthone stereoselectively rearranged on exposure to silica through a diastereoselective process, providing easy access to the complete set of α-hydroxymenthone stereoisomers. The absolute configurations of the four stereoisomers were unambiguously established by IR-VCD and X-ray diffraction, thus clarifying some literature discrepancy. Two of the four stereoisomers could also be obtained through astereoconvergent process, thus avoiding the inherent 50 % yield limitations of such diastereoselective reactions. A solvent-free version allowing an extremely rapid reaction (< 2 h) is also described. Finally, the observed diastereoselection was investigated by DFT calculations. [ABSTRACT FROM AUTHOR]

The structures and absolute configurations of the enantiomers (3a R,8a R)-2,2-dimethyl-4,4,8,8-tetraphenyl-4,5,6,7,8,8a-hexahydro-3a H-1,3-dioxolo[4,5- e][1,3]diazepin-6-one 0.33-hydrate, C32H30N2O3·0.33H2O, (I a), and (3a S,8a S)-2,2-dimethyl-4,4,8,8-tetraphenyl-4,5,6,7,8,8a-hexahydro-3a H-1,3-dioxolo[4,5- e][1,3]diazepin-6-one 0.39-hydrate, C32H30N2O3·0.39H2O, (I b), have been elucidated unambiguously using the complementary power of single-crystal X-ray diffraction (XRD) and vibrational circular dichroism (VCD). The enantiomers crystallize in the Sohncke space group P21212 and pack as dimers stabilized by two symmetric hydrogen bonds involving one amide group each of the cyclic urea moiety. This double interaction is capped by a water molecule that partially occupies a site lying on the twofold axis and forms an uncommon hydrogen bond between the two monomers. A comparison between the solid-state VCD characterizations and the Bayesian statistics on Bijvoet differences determined from the XRD measurements reveals a tendency towards the correct determination of the absolute configuration by this latter method. [ABSTRACT FROM AUTHOR]

The chemical composition of a hexanic extract of Eryngium campestre, obtained from its aerial parts, was investigated by GC-FID, GC/MS, HRMS, NMR and VCD analyses. The main compounds were germacrene D (23.6%), eudesma-4(15)-7-dien-1-β-ol (8.2%) and falcarindiol (9.4%), which are associated with a new uncommon and naturally found 17-membered ring lactone. This 17-membered ring features conjugated acetylenic bonds, named campestrolide (23.0%). The crude extract showed moderate antitrypanosomal (Trypanosoma brucei brucei), antileishmanial (Leishmania mexicana mexicana) and anticancer (cancerous macrophage-like murine cells) activities, and also displayed cytotoxicity, (human normal fibroblasts) in similar concentration ranges (IC50 = 3.0, 3.9, 4.0 and 4.4 µg/mL respectively). Likewise, campestrolide displayed low activity on all tested cells (IC50: 12.5–19.5 µM) except on Trypanosoma, on which it was very active and moderately selective (IC50 = 2.2 µM. SI= 8.9). In conclusion, the new compound that has been described, displaying a singular structure, possesses interesting antitrypanosomal activity that should be further investigated and improved. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including absorption coefficient, hydrogen production, and molecular self-assembling.