14 research outputs found

    Iron-Catalyzed, Chelation-Induced Remote C–H Allylation of Quinolines via 8‑Amido Assistance

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    An iron-catalyzed, 8-amido-enabled regiodivergent C–H allylation of quinolines is described. This reaction represents a rare example of chelation-induced geometrically inaccessible C–H functionalization, allowing for the highly regio- and stereoselective preparation of either the C5- or the C4-allylated quinoline scaffolds regiocontrolled by the catalytic systems

    Regio- and Chemoselective Kumada–Tamao–Corriu Reaction of Aryl Alkyl Ethers Catalyzed by Chromium Under Mild Conditions

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    Acting as an environmentally benign synthetic tool, the cross-coupling reactions with aryl ethers via C–O bond activation have attracted broad interest. However, the functionalizations of C–O bonds are mainly limited to nickel catalysis, and selectivity has long been a prominent challenge when several C–O bonds are present in the one molecule. We report here the first chromium-catalyzed selective cross-coupling reactions of aryl ethers with Grignard reagents by the cleavage of C–O­(alkyl) bonds. Diverse transformations were achieved using simple, inexpensive chromium­(II) precatalyst combining imino auxiliary at room temperature. It offers a new avenue for buildup functionalized aromatic aldehydes with high efficiency and selectivity

    Role of Mono-N-protected Amino Acid Ligands in Palladium(II)-Catalyzed Dehydrogenative Heck Reactions of Electron-Deficient (Hetero)arenes: Experimental and Computational Studies

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    We report here that mono-N-protected amino acids (MPAAs), an important environmentally compatible structural motif, enable acceleration of Pd­(II)-catalyzed dehydrogenative Heck reactions between pyridines and electron-deficient arenes with simple alkenes, leading to diversely functionalized C3- or <i>meta</i>-selective alkenylated pyridines and benzenes via non-chelate-assisted C–H activation. A comprehensive theoretical study by DFT calculations discloses that the amino scaffold of the MPAA ligand facilely converts to an X-type ligand by an initial N–H activation, resulting in a relatively low activation barrier for the C–H cleavage of pyridine. Then a property reversal of the amino group from X-type to L-type ligand allows the alkene substitution to take place smoothly, while the carboxyl group enables the formation of an intramolecular hydrogen bond, significantly decreasing the activation barrier for the carbopalladation. The results of calculations and the kinetic isotopic effect measurement support a rate-limiting C–H activation by a mechanism involving a concerted metalation/deprotonation pathway, with an endothermicity of 31.0 kcal/mol in the process

    Highly Selective Hydrogenation of Aromatic Ketones and Phenols Enabled by Cyclic (Amino)(alkyl)carbene Rhodium Complexes

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    Air-stable Rh complexes ligated by strongly σ-donating cyclic (amino)­(alkyl)­carbenes (CAACs) show unique catalytic activity for the selective hydrogenation of aromatic ketones and phenols by reducing the aryl groups. The use of CAAC ligands is essential for achieving high selectivity and conversion. This method is characterized by its good compatibility with unsaturated ketones, esters, carboxylic acids, amides, and amino acids and is scalable without detriment to its efficiency

    A Comparison of the Performance of the I-gelâ„¢ vs. the LMA-Sâ„¢during Anesthesia: A Meta-Analysis of Randomized Controlled Trials

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    <div><p>Background and Objective</p><p>Conflicting results were found between the I-gel™ and the LMA-Supreme™ during anesthesia, so we conducted a meta-analysis of randomized controlled trials (RCTs) to compare the effectiveness and safety of the I-gel™ vs. the LMA-Supreme™during anesthesia.</p><p>Methods</p><p>A comprehensive search was conducted using Pubmed, EMbase, ISI Web of Knowledge, the Cochrane Library, China Journal Full-text Database, Chinese Biomedical Database, Chinese Scientific Journals Full-text Database, CMA Digital Periodicals, and Google scholar to find RCTs that compare the LMA-S™ with the i-gel™during anesthesia. Two reviewers independently selected trials, extracted data, and assessed the methodological qualities and evidence levels. Data were analyzed by RevMan 5.0 and comprehensive meta-analysis software.</p><p>Results</p><p>Ten RCTs were included. There were no significant differences in oropharyngeal leak pressures (mean difference [MD] 0.72, 95% confidence interval [CI] –1.10 2.53), device placement time (MD –1.3, 95%CI –4.07 1.44), first attempt insertion success (risk ratio [RR] 1.01, 95% CI 0.9 1.14), grade 3 and 4 fiberoptic view (RR 0.89, 95%CI 0.65 1.21), and blood on removal (RR 0.62, 95%CI 0.32 1.22) between the i-gel™ and the LMA-Supreme™, respectively. However, the LMA-Supreme™was associated with easier gastric tube insertion (RR 1.17, 95%CI 1.07 1.29), and more sore throat (RR 2.56, 95%CI 1.60 4.12) than the i-gel™ group.</p><p>Conclusions</p><p>The LMA-Supreme™ and i-gel™ were similarly successful and rapidly inserted. However, the LMA-Supreme™ was shown to be easier for gastric tube insertion and associated with more sore throat compared with the i-gel™.</p></div

    Flow chart demonstrating the process for inclusion in the meta-analysis.

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    <p>Flow chart demonstrating the process for inclusion in the meta-analysis.</p

    Funnel plot of randomized controlled trials.

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    <p>Funnel plot of randomized controlled trials.</p

    Meta-regression results of variables for oropharyngeal leak pressure.

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    <p>Meta-regression results of variables for oropharyngeal leak pressure.</p

    Summary of included studies.

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    <p>Summary of included studies.</p

    Quality assessment of included studies.

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    <p>Quality assessment of included studies.</p