Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)2 Complex

Cooperative roles of Sn(IV) and Cu(II) for efficient transformation of biomass-derived acetol towards lactic acid production

Acetol as one of the major constituent derived from biomass pyrolysis has shown high potential as feedstock to produce chemicals but remains challenging due to the unsatisfied productivity. We here developed a novel technology (Sn(IV)-Cu(II) system), achieving acetol transformation towards lactic acid (LaA) production with an unprecedented yield (91.8 C-mol%), the highest value among the state-of-the-art strategies. The results of experiment and DFT study revealed that [Cu(H₂O)₄]²⁺ and [Sn(OH)₃(H₂O)₃]⁺ were the possible active species, which showed an outstanding synergetic effect. [Cu(H₂O)₄]²⁺ exhibited better ability for acetol activation, and gave more contribution to promote the dehydrogenation oxidation in the terminal carbon and hydroxyl of acetol yielding pyruvaldehyde (PRA). Subsequently, the combination of [Sn(OH)₃(H₂O)₃]⁺ with PRA raised the electrophilicity capacity of terminal C in PRA, thereby facilitating the hydration reaction of PRA so that CH bond energy in the terminal carbon was sharply reduced. This greatly favored the next H-shift from the terminal carbon of hydrated-PRA to adjacent one, allowing LaA synthesis in high productivity. This work might give some important insights for designing new approach to meet the huge demand of LaA in the current market.

Mechanism and Selectivity of Cyclopropanation of 3-Alkenyl-oxindoles with Sulfoxonium Ylides Catalyzed by a Chiral N,N'-Dioxide-Mg(II) Complex

The mechanism and stereoselectivity of an asymmetric cyclopropanation reaction between 3-alkenyl-oxindole and sulfoxonium ylide catalyzed by a chiral N,N'-dioxide-Mg(II) complex were explored using the B3LYP-D3(BJ) functional and the def2-TZVP basis set. The noncatalytic reaction occurred via a stepwise mechanism, with activation barriers of 21.6-23.5 kcal mol^-1. The C₂-C_α bond formed followed by the carbanion S_N2 substitution, constructing a three-membered ring in spiro-cyclopropyl oxindoles, accompanied by the release of dimethylsulfoxide. The electron-withdrawing N-protecting t-butyloxy carbonyl (Boc) and acetyl (Ac) groups in isatin enhanced the local electrophilicity of the C2 atom and the repulsion between the two COPh groups in the reactants, contributing to high reactivity as well as good diastereoselectivity results. The N-Boc-3-phenacylideneoxindole coordinated to the chiral ligand (L-PiPr₂) in a bidentate fashion, forming a hexacoordinate-Mg(II) complex as the reactive species. The origin of enantioselectivity was from the shielding effect of 2,6-diisopropylphenyl groups in the ligand toward the si-face of oxindole. The repulsion between the SO(CH₃)₂ and COPh groups in 3-alkenyl-oxindole and the neighboring ortho-iPr group in the ligand directed the re-face of ylide to attack the re-face of oxindole preferably, contributing to the high diastereoselectivity of the product. A metal-ion-ligand matching relationship was important for a good asymmetric induction effect of the chiral N,N'-dioxide-metal catalyst. A large chiral cavity in the Zn(II) catalyst weakened the shielding effect of 2,6-diisopropylphenyl groups in the ligand toward the prochiral face of oxindole, leading to inferior enantioselectivity observed in the experiment.

Alkyl Enol Ethers: Development in Intermolecular Organic Transformation

Alkyl enol ethers (AEE) are versatile synthetic intermediates with a unique reactivity pattern. This review article summarizes the synthesis of AEE as well as its reactivity and how enol ether undergoes intermolecular reactions for various bond formation, leading to the construction of several useful organic molecules. The synthetic applications of alkyl enol ethers towards intermolecular bond-forming reactions include metal-catalyzed reactions, cycloaddition and heterocycle formation as well as rwactions in the field of natural products synthesis. The achievement of these impressive transformations prove the countless synthetic potential of AEE. The main objective of this review is to bring attentiveness among synthetic chemists to show how AEE extensively can be used to react with both electrophiles as well as nucleophiles, thereby behaving as an ambiphilic reactant. We trust that the unique reactivity pattern of alkyl enol ethers and the fundamental mechanistic idea can attract chemists in AEE chemistry. Exclusively, intermolecular reactions of AEE with other functionalized moieties have not been reviewed to the best of our knowledge.

Organosilanes and their magnetic nanoparticles as naked eye red emissive sensors for Ag+ ions and potent anti-oxidants

This work involves the synthesis of organosilanes as colorimetric sensors for the detection of Ag⁺ ions, cytotoxicity studies and antioxidant activity.

Theoretical investigation on donor–acceptor interaction between a carbonyl compound and an N,N′-dioxide–Sc(iii) complex

The counterion and substituent on amide of the N,N′-dioxide ligand could affect electrostatic energy (ΔV_elstat) as well as orbital energy (ΔE_orb) between CH₂O and Sc(iii)-based catalyst, adjusting the Lewis acidity of the metal centre.

Theoretical and experimental studies on the structure–property relationship of chiral N,N′-dioxide–metal catalysts probed by the carbonyl–ene reaction of isatin

Variation of the linkage or chiral backbone of an N,N′-dioxide ligand adjusts the blocking effect of ortho-iPr on the reaction site, affecting the enantiodifferentiation of two competing pathways.

1,3-Dipolar [3 + 3] cycloaddition of α-halohydroxamate-based azaoxyallyl cations with hydrazonoyl chloride-derived nitrile imines

Promoted by Et₃N, the 1,3-dipolar [3 + 3] cycloaddition of α-halohydroxamate-based azaoxyallylcations with hydrazonoyl chloride-derived nitrile imines occurred efficiently, and furnished desired products in acceptable chemical yields.