Recent developments in isocyanide based multicomponent reactions in applied chemistry

C-H bonds are ubiquitous in organic compounds. It would, therefore, appear that direct functionalization of substrates by activation of C-H bonds would eliminate the multiple steps and limitations associated with the preparation of functionalized starting materials. Regioselectivity is an important issue because organic molecules can contain a wide variety of C-H bonds. The use of a directing group can largely overcome the issue of regiocontrol by allowing the catalyst to come into proximity with the targeted C-H bonds. A wide variety of functional groups have been evaluated for use as directing groups in the transformation of C-H bonds. In 2005, Daugulis reported the arylation of unactivated C(sp(3))-H bonds by using 8-aminoquinoline and picolinamide as bidentate directing groups, with Pd(OAc)2 as the catalyst. Encouraged by these promising results, a number of transformations of C-H bonds have since been developed by using systems based on bidentate directing groups. In this Review, recent advances in this area are discussed.

Catalytic Functionalization of C(sp2) ? H and C(sp3) ? H Bonds by Using Bidentate Directing Groups

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Over the last decade, substantial research has led to the introduction of an impressive number of efficient procedures which allow the selective construction of CC bonds by directly connecting two different CH bonds under oxidative conditions. Common to these methodologies is the generation of the reactive intermediates in situ by activation of both CH bonds. This strategy was introduced by the group of Li as cross-dehydrogenative coupling (CDC) and discloses waste-minimized synthetic alternatives to classic coupling procedures which rely on the use of prefunctionalized starting materials. This Review highlights the recent progress in the field of cross-dehydrogenative C sp 3C formations and provides a comprehensive overview on existing procedures and employed methodologies.

The Cross-Dehydrogenative Coupling of C sp 3H Bonds: A Versatile Strategy for CC Bond Formations

Tremendous advances have been made in nickel catalysis over the past decade Several key properties of nickel, such as facile oxidative addition and ready access to multiple oxidation states, have allowed the development of a broad range of innovative reactions In recent years, these properties have been increasingly understood and used to perform transformations long considered exceptionally challenging Here we discuss some of the most recent and significant developments in homogeneous nickel catalysis, with an emphasis on both synthetic outcome and mechanism

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Recent advances in homogeneous nickel catalysis

ConspectusArene synthesis has been revolutionized by the invention of catalytic cross-coupling reactions, wherein aryl halides can be coupled with organometallic and organic nucleophiles. Although the replacement of aryl halides with phenol derivatives would lead to more economical and ecological methods, success has been primarily limited to activated phenol derivatives such as triflates. Aryl ethers arguably represent one of the most ideal substrates in terms of availability, cost, safety, and atom efficiency. However, the robust nature of the C(aryl)–O bonds of aryl ethers renders it extremely difficult to use them in catalytic reactions among the phenol derivatives.In 1979, Wenkert reported a seminal work on the nickel-catalyzed cross-coupling of aryl ethers with Grignard reagents. However, it was not until 2004 that the unique ability of a low-valent nickel species to activate otherwise unreactive C(aryl)–O bonds was appreciated with Dankwardt’s identification of the Ni(0)/PCy3 system, which signific...

http://pubs.acs.org/doi/pdf/10.1021/acs.accounts.5b00051

Cross-Couplings Using Aryl Ethers via C-O Bond Activation Enabled by Nickel Catalysts.

Palladiumand nickel-catalyzed cross-coupling reactions have been recognized as an indispensable tool for current organic synthesis. Among these reactions, Suzuki–Miyaura coupling is, arguably, of the greatest practical importance of these methods because of the attractive features of organoboronic acids: widespread availability, stability to air and moisture, and low toxicity. Recently, tremendous progress has been made in the development of more elaborate catalyst systems that allow the couplings to be conducted at room temperature, to use unreactive chlorides, and to use alkyl electrophiles. Despite these significant advances, the electrophilic coupling partner for use in Suzuki–Miyaura coupling remains limited, for the most part, to organic halides and sulfonates; although the use of less available electrophiles, including diazonium salts, ammonium salts, aryltriazene/BF3, [7c] azoles, and phosphonium salts has been reported. Aryl methyl ethers, which are as readily available as aryl halides, have never been used in the Suzuki–Miyaura coupling reaction, except for the ruthenium-catalyzed system, which requires a ligating group at the ortho position for the reaction to proceed. Herein, we describe a method for the nickel-catalyzed cross-coupling of aryl methyl ethers with boronic esters [Eq. (1)]. The advantages of using aryl alkyl ethers in the metalcatalyzed cross-coupling reaction have been documented by Wenkert and Dankwardt in the nickel-catalyzed reaction with Grignard reagents (i.e., Kumada–Tamao–Corriutype coupling). Although functional-group compatibility and availability of the starting Grignard reagents for these initial methods are rather limited, these pioneering studies offer a starting point for the development of cross-coupling reactions between aryl methyl ethers and organoboron reagents. Thus, we investigated the reaction of 2-methoxynaphthalene (1a) with organoboron compounds in the presence of a catalytic amount of [Ni(cod)2] (cod= cycloocta-1,5-diene) and PCy3 (Table 1). Whereas attempts with boronic acid (Table 1, entry 1) and borates (Table 1, entries 2 and 3) were unsuccessful, cross-coupling with boronic ester 2a furnished the product in modest yield (Table 1, entry 4). Although the

Nickel‐Catalyzed Cross‐Coupling of Aryl Methyl Ethers with Aryl Boronic Esters

The first catalytic alkynylation of unactivated C(sp3)–H bonds has been accomplished. The method allows for the straightforward introduction of an ethynyl group into aliphatic acid derivatives under palladium catalysis. This new reaction can be applied to the rapid elaboration of complex aliphatic acids, for example, via azide/alkyne cycloaddition.

Palladium-catalyzed direct ethynylation of C(sp3)-H bonds in aliphatic carboxylic acid derivatives.

Two protocols for the nickel-catalyzed cross-coupling of aryl fluorides with aryl boronic esters have been developed. The first employs metal fluoride cocatalysts, such as ZrF(4) and TiF(4), which enable Suzuki-Miyaura reactions of aryl fluorides bearing electron-withdrawing (ketones, esters, and CF(3)), aryl and alkenyl groups as well as those comprising fused aromatic rings, such as fluoronaphthalenes and fluoroquinolines. The second protocol employs aryl fluorides bearing ortho-directing groups, which facilitate the difficult C-F bond activation process via cyclometalation. N-heterocycles, such as pyridines, quinolines, pyrazoles, and oxazolines, can successfully promote cross-coupling with an array of organoboronic esters. A study into the substituent effects with respect to both coupling components has provided fundamental insights into the mechanism of the nickel-catalyzed cross-coupling of aryl fluorides.

Nickel-Catalyzed Suzuki–Miyaura Reaction of Aryl Fluorides

Oxidative coupling between C(sp2)–H bonds and C(sp3)–H bonds is achieved by the Ni(II)-catalyzed reaction of benzamides containing an 8-aminoquinoline moiety as the directing group with toluene derivatives in the presence of heptafluoroisopropyl iodide as the oxidant. The method has a broad scope and shows high functional group compatibility. Toluene derivatives can be used as the coupling partner in an unreactive solvent.

Mamoru Tobisu

Papers

Cross-Couplings Using Aryl Ethers via C-O Bond Activation Enabled by Nickel Catalysts.

Nickel‐Catalyzed Cross‐Coupling of Aryl Methyl Ethers with Aryl Boronic Esters

Palladium-catalyzed direct ethynylation of C(sp3)-H bonds in aliphatic carboxylic acid derivatives.

Nickel-Catalyzed Suzuki–Miyaura Reaction of Aryl Fluorides

Ni(II)-Catalyzed Oxidative Coupling between C(sp2)–H in Benzamides and C(sp3)–H in Toluene Derivatives