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We present a thought-provoking development in chiral resolution. Using a resolving agent of a given handedness, L -proline, we show that both R- and S-enantiomers of mandelic acid can be resolved from a racemic mixture simply by varying the stoichiometry. We are the first to report this specific feature, achieved by the existence of stoichiometrically diverse cocrystal systems between R- and S-mandelic acid and L -proline. [ABSTRACT FROM AUTHOR]

Enantioselective synthesis of synthetically significant (α‐hydroxyallyl)silanes, (α‐hydroxyaryl)silanes, and (α‐hydroxyalkyl)silanes is reported. The present copper‐catalyzed 1,2‐selective hydroborylation of acylsilanes affords the aforementioned products in high yields and with high enantiomeric excesses. This robust and scalable additive‐free catalytic system relies on the use of low copper(II) acetate and diphosphine ligand loadings at room temperature in the presence of a commercially available and bench‐stable hydride source. [ABSTRACT FROM AUTHOR]

We demonstrate the unprecedented phenomenon of solvent-oriented resolution of 1,1′-bi-2-naphtol (Binol). Using a resolution agent of a fixed handedness (R,R)-N,N′-dimethyl-1,2-diphenylethane-1,2-diamine (DADPE), we are able to resolve either the (S)- or (R)-enantiomer of Binol by a mere change of the achiral solvent. [ABSTRACT FROM AUTHOR]

An efficient protocol for the synthesis of enolizable α‐substituted β,γ‐unsaturated aldehydes is reported. The developed strategy involves two steps, epoxidation and Meinwald rearrangement, to result in a one‐carbon homologation of α,β‐unsaturated aldehydes enabling the insertion of a CHR unit. [ABSTRACT FROM AUTHOR]

The goal of this contribution is to guide the reader through the construction and the understanding of quaternary phase diagrams in the pursuit of optimal conditions for a chiral resolution through cocrystallization in solution. The overall description will be illustrated by experimental results on a system involving RS-2-(2-oxopyrrolidin-1-yl) butanamide as chiral API to be separated, and S-mandelic acid as chiral coformer. [ABSTRACT FROM AUTHOR]

We here highlight the importance of stoichiometry for simultaneous cocrystal resolution. Focusing on combining the racemates of binol and proline, we show that a 1 : 2 ratio leads to formation of a full racemic compound, whereas a 2 : 1 ratio, leads to conglomerate formation, with simultaneous resolution of both binol and proline. Playing on stoichiometry, one achieves a reversible switch between the racemic compound and conglomerate. This is the first investigation of such behavior combining two racemates. [ABSTRACT FROM AUTHOR]

Polyphenism is a type of phenotypic plasticity supposedly adaptive to drastic and recurrent changes in the environment such as seasonal alternation in temperate and tropical regions. The butterfly Bicyclus anynana shows polyphenism with well-described wet and dry seasonal forms in sub-Saharan Africa, displaying striking morphological, physiological and behavioural differences in response to higher or lower developmental temperatures. During the seasonal transition in the wild, the intermediate phenotype co-occurs with wet and dry phenotypes. In this study, we aimed to characterize the secondary sexually-selected wing traits of the intermediate form to infer its potential fitness compared to wet and dry phenotypes. Among the previously described wing morphological traits, we first showed that the area of the fifth eyespot on the ventral hindwing is the most discriminant trait to identify wet, dry and intermediate phenotypes in both sexes. Second, we characterized the intermediate form for two secondary sexually-selected wing traits: the area and UV reflectance of the dorsal forewing pupil and the composition of the male sex pheromone. We showed that values of these two traits are often between those of the wet and dry phenotypes. Third, we observed increasing male sex pheromone production in ageing dry and wet phenotypes. Our results contrast with previous reports of values for sexually-selected traits in wet and dry seasonal forms, which might be explained by differences in rearing conditions or sample size effects among studies. Wet, dry and intermediate phenotypes display redundant sexually dimorphic traits, including sexually-selected traits that can inform about their developmental temperature in sexual interactions. [ABSTRACT FROM AUTHOR]

We here report the first occurrence of a preferential cocrystallization process assisted by compressed carbon dioxide. Our study focuses on the Nefiracetam-Mandelic acid conglomerate forming system. The cocrystal conglomerate was successfully crystallized using compressed CO 2 as antisolvent, and acetone, ethyl acetate, or isobutanol as solvents for starting solutions in the so-called GAS process. We then focus on acetone to successfully perform preferential cocrystallization supported by compressed CO 2. A critical step in the design of the process is the adaptation of the set-up to allow the introduction of enantiopure seeding inside the reactor. Based on the use of seeded rings, we test several seeding configurations to enhance enantioseparation through the simultaneous crystallization of both enantiomers in two different areas of the reactor. [Display omitted] • Successful formation of nefiracetam-mandelic acid cocrystal conglomerate using GAS. • Seeding of a pressurized vessel to target the growth of a specific enantiomer. • First proof of concept of preferential cocrystallization assisted by GAS. • Increase of the enantiopurity by seeding two different areas of the vessel. [ABSTRACT FROM AUTHOR]

We report herein the application of polymer brushes for the immobilization of tris[(1,2,3-triazolyl)methyl]amine CuCl catalysts. Well-defined catalytic brushes were prepared through grafting-from and postpolymerization modification approaches on Si surfaces and characterized by X-ray reflectivity, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry. Hairy catalysts of varying thickness and grafting density were investigated in a model CuI-catalyzed azide-alkyne cycloaddition reaction and showed remarkable activity at loadings as low as 0.02 mol % as a result of the unique catalytic site density and nuclearity found in the brush. We demonstrate that thickness and grafting density parameters can be adjusted to maximize catalytic activity along the brush thickness. [ABSTRACT FROM AUTHOR]

We tap into an unexplored area of preferential crystallization, being the first to develop simultaneous chiral resolution of two racemic compounds by preferential cocrystallization. We highlight how the two racemic compounds RS‐mandelic acid (MAN) and RS‐etiracetam (ETI) can be combined together as enantiospecific R‐MAN⋅R‐ETI and S‐MAN⋅S‐ETI cocrystals forming a stable conglomerate system and subsequently develop a cyclic preferential crystallization allowing to simultaneous resolve both compounds. The developed process leads to excellent enantiopurity both for etiracetam (ee>98 %) and mandelic acid (ee≈95 %) enantiomers. [ABSTRACT FROM AUTHOR]

We tap into an unexplored area of preferential crystallization, being the first to develop simultaneous chiral resolution of two racemic compounds by preferential cocrystallization. We highlight how the two racemic compounds RS‐mandelic acid (MAN) and RS‐etiracetam (ETI) can be combined together as enantiospecific R‐MAN⋅R‐ETI and S‐MAN⋅S‐ETI cocrystals forming a stable conglomerate system and subsequently develop a cyclic preferential crystallization allowing to simultaneous resolve both compounds. The developed process leads to excellent enantiopurity both for etiracetam (ee>98 %) and mandelic acid (ee≈95 %) enantiomers. [ABSTRACT FROM AUTHOR]

ortho-Substituted and unsymmetrical 9-phospha-triptycenes were synthesized via two synthetic approaches involving densely functionalized ortho-halogenated triarylmethane or phosphine precursors. ortho-Substituents imposed a considerable steric shielding due to the tricyclic cage-shaped structure with the aryl rings p-systems orthogonal to the phosphorus electron pair. A series of Au(I) and Rh(I) complexes were analysed in the solid state to determine Tolman electronic parameters, cone angles and buried volumes of these unprecedented functionalized phosphines. Quantum chemical calculations of electronic and steric descriptors revealed that these cage-shaped phosphines are electron-poor and that single methyl substituent is enough to provide the largest effect on steric shielding reported so far in triarylphosphines. An unsymmetrically substituted 9-phosphatriptycene was resolved by chiral HPLC, opening the avenue towards stable P-chirogenic triarylphosphines with unlimited configurational stability for new catalyst development in asymmetric transition-metal catalysis. [ABSTRACT FROM AUTHOR]

Processes leading to enantiomerically pure compounds are of utmost importance, in particular for the pharmaceutical industry. Starting from a racemic mixture, crystallization‐induced diastereomeric transformation allows in theory for 100 % transformation of the desired enantiomer. However, this method has the inherent limiting requirement for the organic compound to form a salt. Herein, this limitation is lifted by introducing cocrystallization in the context of thermodynamic deracemization, with the process applied to a model chiral fungicide. We report a new general single thermodynamic deracemization process based on cocrystallization for the deracemization of (R,S)‐4,4‐dimethyl‐1‐(4‐fluorophenyl)‐2‐(1H‐1,2,4‐triazol‐1‐yl)pentan‐3‐one. This study demonstrates the feasibility of this novel approach and paves the way to further development of such processes. [ABSTRACT FROM AUTHOR]

Processes leading to enantiomerically pure compounds are of utmost importance, in particular for the pharmaceutical industry. Starting from a racemic mixture, crystallization‐induced diastereomeric transformation allows in theory for 100 % transformation of the desired enantiomer. However, this method has the inherent limiting requirement for the organic compound to form a salt. Herein, this limitation is lifted by introducing cocrystallization in the context of thermodynamic deracemization, with the process applied to a model chiral fungicide. We report a new general single thermodynamic deracemization process based on cocrystallization for the deracemization of (R,S)‐4,4‐dimethyl‐1‐(4‐fluorophenyl)‐2‐(1H‐1,2,4‐triazol‐1‐yl)pentan‐3‐one. This study demonstrates the feasibility of this novel approach and paves the way to further development of such processes. [ABSTRACT FROM AUTHOR]

This paper describes a tunable and stereoselective dual catalytic system that uses copper and palladium reagents. This cooperative silylcupration and palladium-catalyzed allylation readily affords trisubstituted alkenylsilanes. Fine-tuning the reaction conditions allows selective access to one stereoisomer over the other. This new methodology tolerates different substituents on both coupling partners with high levels of stereoselectivity. The one-pot reaction involving a CuI/Pd0 cooperative dual catalyst directly addresses the need to develop more time-efficient and less-wasteful synthetic pathways. [ABSTRACT FROM AUTHOR]

Tris(tetrathioaryl)methanols and tris(tetrathioaryl)methanes are direct precursors and metabolites, respectively, of tris(tetrathioaryl)methyl radicals, which are very attractive paramagnetic spin probes for many magnetic resonance applications. Due to steric hindrance, these propeller-shaped molecules display slow interconversion between their two enantiomeric conformations (right-handed and left-handed propeller conformations). Syntheses and HPLC resolutions carried out on a chiral stationary phase have been achieved. The influence of the hybridization of the central carbon atom as well as the para substitutient on the conformational stability were experimentally and theoretically studied. Depending on their particular structure, the free activation energy for the isomerization process determined by kinetics of racemization varies from 24.4 to 26.4 kcal mol-1 and corresponds to racemization half-lives of 12 and 343 h, respectively. Computational and NOESY/exchange spectroscopy (EXSY) studies are consistent with a two-ring flip mechanism for the isomerization process of tris(tetrathioaryl)methanols, radicals and tris(tetrathioaryl)methanes. [ABSTRACT FROM AUTHOR]

In this work, we are the first to identify thirteen cocrystals of Nefiracetam, a poor water-soluble nootropic compound. Three of which were obtained with the biocompatible cocrystallization agents citric acid, oxalic acid, and zinc chloride. These latter have been fully structurally and physically characterized and the solubility, dissolution rate, and stability were compared to that of the initial Active Pharmaceutical Ingredient (API). [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "Cu¹/Pd0 Cooperative Dual Catalysis: Tunable Stereoselective Construction of Tetra-Substituted Alkenes" by F. Nahra and others, published in the "Chemistry: A European Journal" in 2014.