Chemo- and Enantioselective Addition and β‑Hydrogen Transfer Reduction of Carbonyl Compounds with Diethylzinc Reagent in One Pot Catalyzed by a Single Chiral Organometallic Catalyst

Using a single chiral phosphoramide–Zn­(II) complex as the catalyst, the asymmetric β-H transfer reduction of aromatic α-trifluoromethyl ketones and enantioselective addition of aromatic aldehydes with Et₂Zn in one pot were successfully realized, affording the corresponding additive products of secondary alcohols in high yields (up to 99%) with excellent enantioselectivities (up to 98% <i>ee</i>) and the reduction products of α-trifluoromethyl alcohols in good to excellent yields with up to 77% <i>ee</i>

Constructing a Quantitative Correlation between N‑Substituent Sizes of Chiral Ligands and Enantioselectivities in Asymmetric Addition Reactions of Diethylzinc with Benzaldehyde

Using the asymmetric addition reaction of diethylzinc with benzylaldehyde as a model, we have demonstrated that excellent correlations exist between steric reference parameters (Charton and Sterimol values) for appropriate sets of substituents present on chiral 1,2-amino-phosphoramide ligands and the enantiomeric ratios of alcohol products produced in this process

Fine-Tuning the Structures of Chiral Diamine Ligands in the Catalytic Asymmetric Aldol Reactions of Trifluoromethyl Aromatic Ketones with Linear Aliphatic Ketones

In this work, we thoroughly investigated the effect of structural differentiation of a series of N,N-disubstituted chiral diamine ligands on the catalytic asymmetric aldol reactions between trifluoromethyl ketones and linear aliphatic ketones for the construction of chiral trifluoromethyl tertiary alcohols. A highly efficient primary–tertiary diamine ligand derived from (1<i>R</i>,2<i>R</i>)-1,2-diphenyl­ethylene­diamine was developed, which catalyzed the reactions with up to 99% yield and up to 94% enantioselectivity in the presence of <i>p</i>-toluene­sulfonic acid (TsOH) using toluene as solvent

Added-Metal-Free Catalytic Nucleophilic Addition of Grignard Reagents to Ketones

On the basis of the investigation of the combinational effect of quaternary ammonium salts and organic bases, an added-metal-free catalytic system for nucleophilic addition reactions of a variety of Grignard reagents to diverse ketones in THF solvent has been developed to produce tertiary alcohols in good to excellent yields. By using tetrabutylammonium chloride (NBu₄Cl) as a catalyst and diglyme (DGDE) as an additive, this system strongly enhances the efficiency of addition at the expense of enolization and reduction. NBu₄Cl should help to shift the Schlenk equilibrium of Grignard reagents to the side of dimeric Grignard reagents to favor the additions of Grignard reagents to ketones via a favored six-membered transition state to form the desired tertiary alcohols, and DGDE should increase the nucleophilic reactivities of Grignard reagents by coordination. This catalytic system has been applied in the efficient synthesis of Citalopram, an effective U.S. FDA-approved antidepressant, and a recyclable version of this catalytic synthesis has also been devised

A Chiral Bisthiourea as a Chiral Solvating Agent for Carboxylic Acids in the Presence of DMAP

A simple chiral bisthiourea has been used as a highly effective and practical chemical solvating agent (CSA) for diverse α-carboxylic acids in the presence of DMAP. Excellent enantiodiscrimination based on well-resolved α-H NMR signals of the enantiomers of carboxylic acids can be obtained without interference from the chiral bisthiourea and DMAP. To check the practicality of the chiral bisthiourea/DMAP for enantiomeric determination, the ee values of mandelic acid (MA) samples over a wide ee range were determined by integration of the α-H signal of MA in ¹H NMR. A discrimination mechanism is proposed, that the formation of two diasteromeric ternary complexes between the chiral bisthiourea and two in situ formed enantiomeric carboxylate-DMAPH⁺ ion pairs discriminates the enantiomers of carboxylic acids. Computational modeling studies show that the chemical shift value of α-H of (<i>S</i>)-MA is greater than that of (<i>R</i>)-MA in ternary complexes, which is consistent with experimental observation. 1D and 2D NOESY spectra demonstrate the intermolecular noncovalent interactions between the protons on the aromatic rings of chiral bisthiourea and α-H of the enantiomers of racemic α-methoxy phenylacetic acids in the complexes

Enhanced Performance of InGaN Light-Emitting Diodes via High-Quality GaN and Embedded Air Voids Grown on Hexagonal 3D Serpentine Mask Sapphire Substrates

This work demonstrates high-efficiency InGaN-based light-emitting diodes (HSM-LEDs) prepared on hexagonal 3D serpentine sapphire substrates. The 3D serpentine mask has a modulating effect on epitaxial lateral growth (ELOG), which can not only reduce the dislocation density (TDD) to 1.7 × 107 cm–2 without any high dislocation density (HDD) region but also induce the formation of a hexagonal pyramidal air-void array with an inclination angle of 65°. Compared to conventional LEDs, HSM-LEDs exhibit a 117% enhancement in EL output power at a current injection of 600 mA. This can be attributed to the improvement of crystal quality by modulated ELOG, the relief of in-plane stresses to mitigate the quantum-confined Stark effect (QCSE) through the weak connection of the epitaxial layer to the substrate, and the enhanced light extraction efficiency by an embedded air-void array. We confirmed the reduction of compressive stress from 0.94 GPa to 0.51 GPa in HSM-LEDs by Raman spectroscopy and investigated the effect of air voids on light extraction efficiency (LEE) experimentally and theoretically. Ray-tracing simulations show that the embedded pyramidal air voids can effectively re-extract the downward emitted light, and the pyramidal air voids with a 65° slant sidewall can improve the LEE by 71%

Flexibly and Repeatedly Modulating Lasing Wavelengths in a Single Core–Shell Semiconductor Microrod

Modulating lasing wavelength flexibly and repeatedly on a single rod is essential to the practical applications of micro/nanorod lasers. In this paper, a structure that decouples the gain medium and optical cavity is proposed, where the corresponding mechanism for the lasing wavelength shift is explained. Based on the above structure, one kind of wavelength continuously variable lasers is achieved on a single GaN/InGaN core–shell microrod without modifying the geometry of the resonant cavity or cutting the microrod. By using this method, lasing wavelength can be modulated from 372 to 408 nm flexibly and repeatedly in a 10 μm facilely synthesized microrod. This approach demonstrates a big application potential in numerous fields consisting of optical telecommunication and environmental monitoring