4 research outputs found

    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

    Pd(II)-Catalyzed Intermolecular Arylation of Unactivated C(sp<sup>3</sup>)–H Bonds with Aryl Bromides Enabled by 8‑Aminoquinoline Auxiliary

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    An example of using readily available, less reactive aryl bromides as arylating reagents in the Pd­(II)-catalyzed intermolecular arylation of unactivated C­(sp<sup>3</sup>)–H bonds is described. This reaction was promoted by a crucial 8-aminoquinolinyl directing group and a K<sub>2</sub>CO<sub>3</sub> base, enabling regiospecific installation of an aryl scaffold at the β-position of carboxamides. A mechanistic study by DFT calculations reveals a C­(sp<sup>3</sup>)–H activation-led pathway featuring the oxidative addition as the highest energy transition state

    Arynes Double Bond Insertion/Nucleophilic Addition with Vinylogous Amides and Carbodiimides

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    Arynes are shown to insert into some CX double bonds, leading to benzannulated four-membered rings. The strain of these rings allow for a ready, spontaneous opening to afford <i>o</i>-quinomethide analogues. Subsequent nucleophilic addition re-aromatizes the intermediates to achieve <i>ortho</i>-difunctionalization of arynes. In this report, we describe the aryne insertion into the CC double bonds of vinylogous amides and the CN double bonds of carbodiimides. The correlation and comparison with aryne single bond insertion chemistry will be discussed. Computational studies for the ring-opening step, as well as the nature of the <i>o</i>-quinomethide intermediates, will also be discussed