Branched selectivity in asymmetric allylic C−H alkylation is enabled by using 2‐acylimidazoles as nucleophiles in the presence of a chiral phosphoramidite‐palladium catalyst. A wide range of terminal ...alkenes, including 1,4‐dienes and allylarenes, are nicely tolerated and provide chiral 2‐acylimidazoles in moderate to high yields and with high levels of regio‐, and enantio‐, and E/Z‐selectivities. Mechanistic studies using density‐functional theory calculations suggest a nucleophile‐coordination‐enabled inner‐sphere attack mode for the enantioselective carbon–carbon bond‐forming event.
Branching out: Palladium‐chiral phosphoramidite catalysis is used for an unprecedented branched‐selective asymmetric allylic C−H alkylation by using 2‐acylimidazoles as model coordinating nucleophiles. Density‐functional theory calculations suggest an unusual inner‐sphere mechanism for the carbon–carbon bond‐forming process.
Ring‐opening polymerization (ROP) offers a striking solution to solve problems encountered in step‐growth condensation polymerization, including precise control over molecular weight, molecular ...weight distribution, and topology. This has inspired our interest in ROP of cycloalkanes with an ultimate goal to rethink polyolefins, which clearly poses a number of challenges. Practicality of ROP of cycloalkanes is actually limited by their low polymerizability and elusive mechanisms which arise from significantly varied ring size and non‐polar C−C bonds in monomers. In this work, by using Lewis acid/Brønsted base/C(sp3)‐H initiator system previously developed in our laboratory, we focus on cyclobutanes and explore the positional and electronic effects of substituents on the ring, namely electron push‐pull effect, in promoting controlled polymerization to afford densely functionalized poly(cyclobutanes), as well as catalytic degradation of obtained polymers for upcycling. More importantly, experiments and DFT calculations unveil considerable population of Lewis‐acid‐induced thermostabilized 1,4‐zwitterions, which distinguish cyclobutanes from cyclopropanes and others. All these findings would shed light on catalytic synthesis and degradation of saturated all‐carbon main‐chain polymers, as well as small molecule transformations of cyclobutanes.
DFT calculations guide to unveil the electron push‐pull effect in reshaping the polymerizability of non‐polymerizable cyclobutane to afford densely functionalized all‐carbon main‐chain polymers, as well as their degradation to afford alkene derivatives. Successful polymerization conditions consist of Lewis acid, Brønsted base, and a C(sp3)‐H initiator, while degradation proceeds with catalytic amount of an acid.
Amine/Pd(II) cooperative catalysis has enabled a highly enantioselective addition of cyclic ketones to unactivated alkenes. The hallmark of the strategy includes amide-directed, regioselective ...activation of alkenes by Pd(II) and enhancing the nucleophilicity of α-carbon of the ketones by enamine catalysis to synergistically drive the reaction, which is basically unable to be accessed by a single catalyst. The combination of a commercially available Pd(II) catalyst and diphenylprolinol was able to provide the γ-addition products with good to high yields and efficient stereochemical control (up to 95% ee).
Quantum chemical calculations were used to determine the energetic viability of several mechanisms for formation of ladderanes from oligocyclopropanes. Pathways involving radical cations, diradicals, ...and carbocations were considered, and a hybrid of carbocation and radical cation pathways was predicted to have the lowest overall barrier.
A 4+2 cycloaddition reaction proceeding through tandem cross‐dehydrogenative coupling/intramolecular hydroarylation between N‐aryltetrahydroisoquinolines and crotonaldehyde was developed by virtue of ...enamine–iminium catalysis, which enabled the rapid construction of ring‐fused tetrahydroquinolines. The first metal‐free catalytic oxidative coupling of γ‐selective C(sp3)–H bonds of crotonaldehyde was realized by using a secondary amine catalyst and 2,3‐dichloro‐5,6‐dicyanoquinone.
Tandem oxidative cross‐dehydrogenative coupling/intramolecular hydroarylation between N‐aryltetrahydroisoquinolines and crotonaldehyde enables the rapid construction of ring‐fused tetrahydroquinolines. The first metal‐free catalytic oxidative coupling of γ‐selective C(sp3)–H bonds of crotonaldehyde is realized by using a secondary amine catalyst and 2,3‐dichloro‐5,6‐dicyanoquinone (DDQ).
An enantioselective α-amination of esters by a Lewis base/copper(I) cooperative catalysis strategy has been developed. The transient chiral C1-ammonium enolate generated from pentafluorophenyl ester ...and nucleophilic Lewis base is nicely compatible with the copper intermediate formed from N,N-di-t-butyldiaziridinone and Cu(I) to allow for high levels of stereochemical control. The cooperative catalytic reaction leads to a diverse set of highly enantioenriched hydantoins in good yields with excellent enantioselectivities (90–99% ee).
In the present study, thermal hazards of TNT and DNAN used as the molten binder in TKX-50-based melt-cast explosives were comparatively studied through accelerating rate calorimeter (ARC) and ...Cook-off experiments. Two kinds of ARC operation modes were performed to investigate the thermal safety performance under adiabatic conditions (HWS mode) and constant heating (CHR mode). The obtained results demonstrated that at both heating modes, DNAN/TKX-50 outperformed TNT/TKX-50 from the thermal safety point of view. However, the sensitivity to heat of the samples was reverse because of the different heating modes. In addition, the results of thermal hazard assessment obtained from the cook-off experiment complied with ARC analysis which indicated the molten binder TNT replaced by DNAN would reduce the hazard of the TKX-50 melt cast explosive. Furthermore, the results of cook-off experiments also showed that DNAN/TKX-50 outperformed TNT/TKX-50 from the aspect of thermal stability, which was consistent with the result of CHR mode because of the similar heating process.
Herein, we describe an example of catalytic asymmetric synthesis of sulfinamides. Aromatic sulfenamides were chosen as useful substrates, because of the indispensable N–H bond, which could form an ...efficient hydrogen bond with chiral phosphoric acid. H2O2 (35%) was used as the terminal oxidant for preparation of sulfinamides in high yields and enantioselectivities, which could be easily derivatized to sulfoxides and other sulfinamides without loss of the enantioselectivity.
This study was conducted to reveal the effects of silicon (Si) application on nutrient utilization efficiency by rice and on soil nutrient availability and soil microorganisms in a hybrid rice ...double-cropping planting system. A series of field experiments were conducted during 2017 and 2018. The results showed that Si nutrient supply improved grain yield and the utilization rates of nitrogen (N) and phosphorus (P) to an appropriate level for both early and late plantings, reaching a maximum at 23.4 kg/ha Si. The same trends were found for the ratios of available N (AN) to total N (TN) and available P (AP) to total P (TP), the soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and the ratios of MBN to TN and MBP to TP, at different levels of Si. Statistical analysis further revealed that Si application enhanced rice growth and increased the utilization rate of fertilizer due to an ecological mechanism, i.e., Si supply significantly increased the total amount of soil microorganisms in paddy soil compared to the control. This promoted the mineralization of soil nutrients and improved the availability and reserves of easily mineralized organic nutrients.
Computational catalyst design requires identification of a metal and ligand that together result in the desired reaction reactivity and/or selectivity. A major impediment to translating computational ...designs to experiments is evaluating ligands that are likely to be synthesized. Here, we provide a solution to this impediment with our ReaLigands library that contains >30,000 monodentate, bidentate (didentate), tridentate, and larger ligands cultivated by dismantling experimentally reported crystal structures. Individual ligands from mononuclear crystal structures were identified using a modified depth-first search algorithm and charge was assigned using a machine learning model based on quantum-chemical calculated features. In the library, ligands are sorted based on direct ligand-to-metal atomic connections and on denticity. Representative principal component analysis (PCA) and uniform manifold approximation and projection (UMAP) analyses were used to analyze several tridentate ligand categories, which revealed both the diversity of ligands and connections between ligand categories. We also demonstrated the utility of this library by implementing it with our building and optimization tools, which resulted in the very rapid generation of barriers for 750 bidentate ligands for Rh-hydride ethylene migratory insertion.
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