Chiral Research Articles

New chiral melatonin-derivatives as multitarget directed ligands to treat Alzheimer’s disease.

New chiral melatonin-derivatives as multitarget directed ligands to treat Alzheimer’s disease.

Complex of a new racemic thiourea substrate: Spectrophotometric study and separation of atropisomers

The activity of a chiral molecule can vary from one atropisomer to the other. In this study, the separation of racemic-N-(2-methylphenyl), N’-(2-chlorophenyl) thiourea (H 2 L 2 ), a hydrophobic heavy metal trap, has been studied using reversed-phase high-performance liquid chromatography (RP-HPLC) with hydroxypropyl-beta-cyclodextrin (HP-β-CD) as a complexing additive to the racemic mixture and hexane-isopropanol as a mobile phase. The stoichiometry and the overall association constant of the complex have been determined using the continuous variation (Job's plot) method and the Scott's method respectively.

Device-Compatible Chiroptical Surfaces through Self-Assembly of Enantiopure Allenes.

Chiroptical methods have been proven to be superior compared to their achiral counterparts for the structural elucidation of many compounds. To expand the use of chiroptical systems to everyday applications, the development of functional materials exhibiting intense chiroptical responses is essential. Particularly, tailored and robust interfaces compatible with standard device operation conditions are required. Herein, we present the design and synthesis of chiral allenes and their use for the functionalization of gold surfaces. The self-assembly results in a monolayer-thin room-temperature-stable upstanding chiral architecture as ascertained by ellipsometry, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure. Moreover, these nanostructures anchored to device-compatible substrates feature intense chiroptical second harmonic generation. Both straightforward preparation of the device-compatible interfaces along with their chiroptical nature provide major prospects for everyday applications.

Catalytic Enantioselective Simultaneous Control of Axial Chirality and Central Chirality in Allenes

AbstractChiral molecules, which may contain one or more different type(s) of stereocentres, such as central, axial, planar, and helical chiralities, etc., are indispensable in chemistry, pharmaceutical industry, and life science. Despite many advances for the preparation of chiral molecules usually with a single type of chirality have been realized, simultaneous construction of different types of chiralities is still a significant challenge. Here, we wish to report a protocol for preparation of chiral allenes with both central and axial chiralities via a catalytic asymmetric allenylation of different biologically or synthetically useful fluorinated or non‐fluorinated nucleophiles with readily available racemic allenes by using a single chiral ligand. An echoing between the central chirality and axial chirality for the enantioselectivity was observed. This strategy provides a general and practical approach to functionalized optically active allenes bearing both central and axial chiralities with an excellent enantioselectivity under mild conditions.

Supramolecular Chiral Self-Assembly Based on Small Molecular Natural Products

Supramolecular Chiral Self-Assembly Based on Small Molecular Natural Products

Solvent-Dependent Asymmetric Synthesis of Alkynyl and Monofluoroalkenyl Isoindolinones by CpRhIII -Catalyzed C-H Activation.

The asymmetric synthesis of alkynyl and monofluoroalkenyl isoindolinones from N-methoxy benzamides and α,α-difluoromethylene alkynes is enabled by C-H activation with a chiral CpRhIII catalyst. Remarkably, product formation is solvent-dependent; alkynyl isoindolinones are afforded in MeOH (up to 86 % yield, 99.6 % ee) whereas monofluoroalkenyl isoindolinones are generated in i PrCN (up to 98:2 Z/E, 93 % yield, 86 % ee). Mechanistic studies revealed chiral allene and E-configured alkenyl rhodium species as reaction intermediates. The latter is transformed into the corresponding Z-configured monofluoroalkene upon protonation in the i PrCN system and into an alkyne by an unusual anti β-F elimination in the MeOH system. Notably, kinetic resolution processes occur in this reaction. Despite the moderate enantiocontrol for the formation of the chiral allene, the Z-monofluoroalkenyl isoindolinones and alkynyl isoindolinones were obtained in good enantiopurities by one or two sequential kinetic resolution processes.

Living and enantiomer-selective polymerization of allene initiated by Ni complex containing chiral phosphine

A new allylnickel(II) complex ([S(R)]-N-[(1S)-2-(diphenylphosphino)-1-phenylethyl]-2-methyl-2-propanesulfinamide)​(2,​2,​2-​trifluoroacetato-​κO)​(π-allyl)​nickel (2) was designed and prepared by using chiral phosphine. 2 was revealed to efficiently initiate the polymerization of l- and d-N-(1-(dodecylamino)-1-oxopropan-2-yl)-4-(propa-1,2-dien-1-yloxy)-benzamide (l-1 and d-1) in a living/controlled chain growth manner. Polymerization kinetics of l-1 and d-1 indicated that l-1 preferentially polymerized over the antipode d-1 by a factor of 1.9. In block copolymerization of rac-1 using the poly-l-150 as the macroinitiator, the polymerization proceeded in enantiomer-selective manner. It was found that enantiomeric excess (ee) value of the recovered monomer increased with the monomer conversion and finally reached to the maximum of 34%. These results suggest this chiral phosphine complex exhibits enantiomer-selectivity for the polymerization of chiral allene derivative monomer.

Solvent‐Dependent Asymmetric Synthesis of Alkynyl and Monofluoroalkenyl Isoindolinones by CpRhIII‐Catalyzed C−H Activation

AbstractThe asymmetric synthesis of alkynyl and monofluoroalkenyl isoindolinones from N‐methoxy benzamides and α,α‐difluoromethylene alkynes is enabled by C−H activation with a chiral CpRhIII catalyst. Remarkably, product formation is solvent‐dependent; alkynyl isoindolinones are afforded in MeOH (up to 86 % yield, 99.6 % ee) whereas monofluoroalkenyl isoindolinones are generated in iPrCN (up to 98:2 Z/E, 93 % yield, 86 % ee). Mechanistic studies revealed chiral allene and E‐configured alkenyl rhodium species as reaction intermediates. The latter is transformed into the corresponding Z‐configured monofluoroalkene upon protonation in the iPrCN system and into an alkyne by an unusual anti β‐F elimination in the MeOH system. Notably, kinetic resolution processes occur in this reaction. Despite the moderate enantiocontrol for the formation of the chiral allene, the Z‐monofluoroalkenyl isoindolinones and alkynyl isoindolinones were obtained in good enantiopurities by one or two sequential kinetic resolution processes.

Allenedicarboxylate as a Stereochemically Labile Electrophile for Chiral Organic Base-catalyzed Stereoselective Michael Addition

Abstract A highly stereoselective Michael addition of α-amino acid-derived 2-benzyloxythiazol-5(4H)-ones to dimethyl allenedicarboxylate was developed by employing P-spiro chiral triaminoiminophosphorane bearing (S)-sec-butyl groups as a catalyst. Theoretical investigation of the transition-state models for the reaction and control experiments suggested the intervention of a dynamic kinetic resolution of the axially chiral allene acceptor. The synthetic utility of this method was demonstrated through the transformation of the stereochemically homogeneous Michael adduct to an α-vinylic α-amino acid derivative.

Light-induced multi-wavelength lasing in dye-doped chiral nematic liquid crystals due to strong pumping illumination

ABSTRACTThe influence of the pump laser beam on the lasing spectral characteristics in dye-doped cholesteric liquid crystal is investigated. Under the influence of the pump laser pulses with different repetition rates and energies, non-linear reorientation and light-induced flow reorientation of chiral nematic liquid crystals (CLC) molecules was observed. Independent of the reorientation mechanism, multi-wavelength lasing was achieved due to stepwise uncoiling of the CLC structure. Under the influence of a pump laser beam with low repetition rate, Cano–Grandjean disclination defect lines were induced which remain even after removal of the laser beam.

Preparation and Application of Novel Bonded L -Valine and L -Alanine Derived Chiral Stationary Phases

Preparation and Application of Novel Bonded L -Valine and L -Alanine Derived Chiral Stationary Phases

Free vibration analysis of chiral double-walled carbon nanotube embedded in an elastic medium using non-local elasticity theory and Euler Bernoulli beam model

The transverse free vibration of chiral double-walled carbon nanotube (DWCNTs) embedded in elastic medium is modeled by the non-local elasticity theory and Euler Bernoulli beam model. The governing equations are derived and the solutions of frequency are obtained. According to this study, the vibrational mode number, the small-scale coefficient, the Winkler parameter and chirality of double-walled carbon nanotube on the frequency ratio (xN) of the (DWCNTs) are studied and discussed. The new features of the vibration behavior of (DWCNTs) embedded in an elastic medium and the present solutions can be used for the static and dynamic analyses of double-walled carbon nanotubes.

Correction: Guest-regulated chirality switching of planar chiral pseudo[1]catenanes.

Correction for 'Guest-regulated chirality switching of planar chiral pseudo[1]catenanes' by Ya-Fen Yang et al., Org. Biomol. Chem., 2018, DOI: 10.1039/c8ob00156a.

A Review of Chirality Finding Techniques of DWCNT

A Review of Chirality Finding Techniques of DWCNT

Correction: Synthetic routes for a variety of halogenated (chiral) acetic acids from diethyl malonate (vol 7, pg 55434, 2017)

Correction: Synthetic routes for a variety of halogenated (chiral) acetic acids from diethyl malonate (vol 7, pg 55434, 2017)

Highly Selective Manganese(I)/Lewis Acid Cocatalyzed Direct C-H Propargylation Using Bromoallenes.

A manganese(I)/Lewis acid cocatalyzed direct C-H propargylation with high selectivity has been developed. BPh3 was discovered to not only promote the reactivity, but also enhance the selectivity. Secondary, tertiary, and even quaternary carbon centers at the propargylic position could be directly constructed. Both internal and terminal alkynes are easily accessible. The chirality was successfully transferred from an axially chiral allene to central chirality. The reactivity of the manganese catalyst in this reaction was found to be unique among transition metal catalysts.

Hurdles in exploring chirality in co-crystallization

Hurdles in exploring chirality in co-crystallization

A cis-to-trans switch in DTD-like fold relaxes substrate chiral specificity

A <i>cis</i>-to-<i>trans</i> switch in DTD-like fold relaxes substrate chiral specificity

Reactions of Chiral N-Tert-Butanesulfinyl Imines with Ethyl Nitroacetate

We thank the continued financial support from our Ministerio de Ciencia e Innovacion (MICINN; projects CTQ2010-20387, CONSOLIDER INGENIO 2010-CDS2007-00006, CTQ2011-24165), the Ministerio Economia y Competitividad (MINECO; projects CTQ2014-53695-P, CTQ2014-51912-RED), FEDER, Generalitat Valenciana (PROMETEO 2009/039, PROMETEOII/2014/017) and the University of Alicante.

Chiral Rhodium-Catalyzed Asymmetric [2+2] Photocycloaddition

Chiral Rhodium-Catalyzed Asymmetric [2+2] Photocycloaddition