CaCl2, Bisoxazoline, and Malonate: A Protocol for an Asymmetric Michael Reaction

NBS/DBU-Promoted One-Pot Three-Component Cycloaddition of Malonic Acid Derivatives, Nitrosoarenes, and Alkenes: Synthesis of Isoxazolidines

A general DBU-mediated one-pot three-component cycloaddition reaction of easily accessible malonic acid derivatives, nitrosoarenes, and alkenes has been successfully established with the aid of NBS to provide direct access to highly functionalized isoxazolidine derivatives with generally good to excellent yields, broad functional group tolerance, and excellent regio- and diastereo-selectivities under mild conditions. The mechanism study shows that the NBS-mediated formation of bromomalonic acid derivatives from malonic acid derivatives and DBU-promoted synthesis of nitrone intermediates via the reaction of bromomalonic acid derivatives with nitrosoarenes are key steps.

Enantioselective Michael Addition of Malonates to Enones

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Many catalysts were tested in asymmetric Michael additions in order to synthesize enantioenriched products. One of the most common reaction types among the Michael reactions is the conjugated addition of malonates to enones making it possible to investigate the structure–activity relationship of the catalysts. The most commonly used Michael acceptors are chalcone, substituted chalcones, chalcone derivatives, cyclic enones, while typical donors may be dimethyl, diethyl, dipropyl, diisopropyl, dibutyl, di-tert-butyl and dibenzyl malonates. This review summarizes the most important enantioselective catalysts applied in these types of reactions.

Lithium Binaphtholate-Catalyzed Michael Reaction of Malonates with Maleates and Its Application to the Enantioselective Synthesis of Tricarboxylic Acid Derivatives

The Michael reaction of malonates with maleates afforded the corresponding adducts in high yields with high enantioselectivities (up to 98% enantiomeric excess (ee)) by using dilithium 3,3'-dichlorobinaphtholate as a catalyst. The obtained Michael adducts could be converted to optically active tricarboxylic acid (TCA) derivatives via the Krapcho reaction.

Asymmetric diastereodivergent Michael addition of 2-chloromalonate esters to conjugated imines enabled by catalyst metal change

A change of the metal ion in pyBOX complex catalysts enables the asymetric diastereodivergent conjugate addition of 2-chloromalonate esters to β,γ-unsaturated α-ketiminoesters.

Crystal structure and Hirshfeld surface analysis of diethyl 2-[4-(4-fluoro-phen-yl)-2-methyl-4-oxobutan-2-yl]malonate

The title compound, C18H23FO5, was synthesized by reacting diethyl malonate with 1-(4-fluoro-phen-yl)-3-methyl-but-2-en-1-one. The mol-ecule adopts a loose conformation stabilized by weak C-H⋯O and C-H⋯π inter-actions. In the crystal, the mol-ecules are joined by C-H⋯O contacts into infinite chains along the b-axis direction with a C(6) graph-set motif. Hirshfeld surface analysis and fingerprint plots demonstrate the predominance of H⋯H, O⋯H and F⋯H inter-molecular inter-actions in the crystal structure.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Mechanistic Study on Water Splitting Reactions by Small Silicon Clusters Si3X, X = Si, Be, Mg, Ca

Interaction, dissociation, and dehydrogenation reactions of water monomer and dimer with pure and mixed tetrameric silicon clusters Si₃X with X = Si, Be, Mg, Ca were investigated using high accuracy quantum chemical calculations. While geometries were optimized using the DFT/B3LYP functional with the aug-cc-pVTZ basis set, reaction energy profiles were constructed making use of the coupled-cluster theory with extrapolation to complete basis set, CCSD(T)/CBS. Cleavage of the O-H bond in water dimer is found to be more favored than that of water monomer in the reaction with Si₄. The water acceptor monomer in water dimer performs as an internal catalyst facilitating H atom transfer to form H₂. Adsorption of water dimer on Si₃X clusters mostly takes place upon interaction of the donor water molecule with Si cluster. Water dimer adsorbs more strongly on Si₃M than on Si₄. The most stable complexes obtained upon interaction of water dimer with Si₃M mainly arise from M-O interaction in preference over a Si-O connection. Substitution of a Si atom in Si₄ by an earth alkaline metal induces a substantial reduction of the energy barrier for the (rate-limiting) first O-H bond cleavage of water dimer. The most remarkable achievement upon doping is a disappearance of the overall energy barrier for the initial O-H bond cleavage in water dimer. Of the three binary Si₃M clusters considered, dehydrogenation of water dimer driven by Si₃Be is the most kinetically and thermodynamically favorable pathway. In comparison to another cluster such as Al₆ and nanoparticles Ru₅₅, energy barriers for water dimer dissociation on Si₃M are much lower. The mixed clusters Si₃M turn out to be as efficient alternative reagents for O-H dissociation and hydrogen production from water dimer. This study proposes further searches for other mixed silicon clusters as realistic gas phase reagents for crucial dehydrogenation processes in such a way they can be prepared and conducted in experiment.

Chalcone: A Privileged Structure in Medicinal Chemistry

Privileged structures have been widely used as an effective template in medicinal chemistry for drug discovery. Chalcone is a common simple scaffold found in many naturally occurring compounds. Many chalcone derivatives have also been prepared due to their convenient synthesis. These natural products and synthetic compounds have shown numerous interesting biological activities with clinical potentials against various diseases. This review aims to highlight the recent evidence of chalcone as a privileged scaffold in medicinal chemistry. Multiple aspects of chalcone will be summarized herein, including the isolation of novel chalcone derivatives, the development of new synthetic methodologies, the evaluation of their biological properties, and the exploration of the mechanisms of action as well as target identification. This review is expected to be a comprehensive, authoritative, and critical review of the chalcone template to the chemistry community.

Two Catalytic Methods of an Asymmetric Wittig [2,3]-Rearrangement

Two different approaches for asymmetric catalytic Wittig [2,3]-rearrangement were developed. Allyloxymalonate derivatives were converted into homoallyl alcohols via organocatalytic or Ca²⁺-catalyzed pathways in moderate to high enantioselectivities.