A Convergent Synthesis of Functionalized Alkenyl Halides through Cobalt(III)‐Catalyzed Three‐Component C−H Bond Addition

A Co^III‐catalyzed three‐component coupling of C(sp²)−H bonds, alkynes, and halogenating agents to give alkenyl halides is reported. This transformation proceeds with high regio‐ and diastereoselectivity, and is effective for a broad range of aryl and alkyl terminal alkynes. Diverse C−H bond partners also exhibit good reactivity for a range of heteroaryl and aryl systems as well as synthetically useful secondary and tertiary amide, urea, and pyrazole directing groups. This multicomponent transformation is also compatible with allenes in place of alkynes to furnish tetrasubstituted alkenyl halides, showcasing the first halo‐arylation of allenes.     

Thioamide‐Directed Cobalt(III)‐Catalyzed Selective Amidation of C(sp3)−H Bonds

A mild, oxidant‐free, and selective Cp*Co^III‐catalyzed amidation of thioamides with robust dioxazolone amidating agents via C(sp³)−H bond activation to generate the desired amidated products is reported. The method is efficient and allows for the C−H amidation of a wide range of functionalized thioamides with aryl‐, heteroaryl‐, and alkyl‐substituted dioxazolones under the Cp*Co^III‐catalyzed conditions. The observed regioselectivity towards primary C(sp³)−H activation is supported by computational studies and the cyclometalation is proposed to proceed by means of an external carboxylate‐assisted concerted metalation/deprotonation mechanism. The reported method is a rare example of the use of a directing group other than the commonly used pyridine and quinolone classes for Cp*Co^III‐catalyzed C(sp³)−H functionalization and the first to exploit thioamides.     

Dehydrogenative N‐Incorporation: A Direct Approach to Quinoxaline N‐Oxides under Mild Conditions

An efficient method for the synthesis of quinoxaline N‐oxides proceeds by the dehydrogenative N‐incorporation of simple imines by C(sp²)? H and C(sp³)? H bond functionalization. The overall transformation involves the cleavage of three C? H bonds. The reaction is easily handled and proceeds under mild conditions. Simple and readily available tert‐butyl nitrite (TBN) was employed as the NO source.     

Rhodium(I)‐Catalyzed Sequential C(sp)C(sp3) and C(sp3)C(sp3) Bond Formation through Migratory Carbene Insertion

A Rh^I‐catalyzed three‐component reaction of tert‐propargyl alcohol, diazoester, and alkyl halide has been developed. This reaction can be considered as a carbene‐involving sequential alkyl and alkynyl coupling, in which C(sp)? C(sp³) and C(sp³)? C(sp³) bonds are built successively on the carbenic carbon atom. The Rh^I‐carbene migratory insertion of an alkynyl moiety and subsequent alkylation are proposed to account for the two separate C? C bond formations. This reaction provides an efficient and tunable method for the construction of all‐carbon quaternary center.     

Copper‐Catalyzed Site‐Selective Intramolecular Amidation of Unactivated C(sp3)H Bonds

The intramolecular dehydrogenative amidation of aliphatic amides, directed by a bidentate ligand, was developed using a copper‐catalyzed sp³ C? H bond functionalization process. The reaction favors predominantly the C? H bonds of β‐methyl groups over the unactivated methylene C? H bonds. Moreover, a preference for activating sp³ C? H bonds of β‐methyl groups, via a five‐membered ring intermediate, over the aromatic sp² C? H bonds was also observed in the cyclometalation step. Additionally, sp³ C? H bonds of unactivated secondary sp³ C? H bonds could be functionalized by favoring the ring carbon atoms over the linear carbon atoms.     

Cp*RhIII‐Catalyzed Arylation of C(sp3)H Bonds

The first Cp*Rh^III‐catalyzed arylation of unactivated C(sp³)? H bonds is presented. The unactivated primary C(sp³)? H bond of 2‐alkylpyridines can be activated by Rh^III and further reacts with triarylboroxines to efficiently build new C(sp³)? aryl bonds. The methodology also provides a facile and efficient synthesis of unsymmetrical triarylmethanes by Rh^III‐catalyzed C(sp³)? H arylation of diarylmethanes.     

Nickel‐Catalyzed Site‐Selective Amidation of Unactivated C(sp3)H Bonds

Intramolecular dehydrogenative cyclization of aliphatic amides was achieved on unactivated sp³ carbon atoms by a nickel‐catalyzed C?H bond functionalization process with the assistance of a bidentate directing group. The reaction favors the C?H bonds of β‐methyl groups over the γ‐methyl or β‐methylene groups. Additionally, a predominant preference for the β‐methyl C?H bonds over the aromatic sp² C?H bonds was observed. Moreover, this process also allows for the effective functionalization of benzylic secondary sp³ C?H bonds.     

Diastereocontrolled Monoprotodeboronation of β‐Sulfinimido gem‐Bis(boronates): A General and Stereoselective Route to α,β‐Disubstituted β‐Aminoalkylboronates

β‐Aminoalkylboronic acids are bioisosteres of the pharmaceutically important class of β‐amino acids but few stereoselective methods exist for their preparation. The 1,2‐addition of lithiated 1,1‐diborylalkanes onto chiral N‐tert‐butanesulfinyl aldimines produces β‐sulfinimido gem‐bis(boronates) in good to excellent yields with high diastereoselectivity. The optimized conditions involve the use of rubidium fluoride and water, and are compatible with functionalized alkyl, aryl, alkenyl, and alkynyl substituents. Under these conditions, the geminal quaternary alkyl bis(pinacolatoboryl) intermediates undergo a highly diastereoselective monoprotodeboronation to afford a wide range of syn‐α,β‐disubstituted β‐aminoalkylboronates. This novel application of protodeboronation chemistry was shown to result from a kinetically controlled, diastereotopic‐group‐selective B?C bond protolysis dictated by the configuration of the adjacent stereogenic C?N center. Facile acidic cleavage of the sulfinimide auxiliary produces the free aminoboronates with high enantiomeric purity.     

Visible Light Induced Rhodium(I)‐Catalyzed C−H Borylation

An efficient visible light induced rhodium(I)‐catalyzed regioselective borylation of aromatic C?H bonds is reported. The photocatalytic system is based on a single NHC?Rh^I complex capable of both harvesting visible light and enabling the bond breaking/forming at room temperature. The chelating nature of the NHC‐carboxylate ligand was critical to ensure the stability of the Rh^I complex and to provide excellent photocatalytic activities. Experimental mechanistic studies evidenced a photooxidative ortho C?H bond addition upon irradiation with blue LEDs, leading to a cyclometalated Rh^III‐hydride intermediate.     

Highly Selective Addition of a Broad Spectrum of Trimethylsilane Pro‐nucleophiles to N‐tert‐Butanesulfinyl Imines

Addition of organotrimethylsilane reagents to chiral N‐tert‐butanesulfinyl imines can be achieved in good yields and with excellent diastereoselectivities by employing TMSO^?/Bu₄N⁺ as a Lewis base activator in THF. A variety of aliphatic, aromatic, heteroaromatic and organometallic chiral imines were utilised as electrophiles for the synthesis of enantioenriched N‐tert‐butanesulfinyl amides. Remarkably, the same sets of reaction conditions could be used with a highly diverse range of bench‐stable organotrimethylsilane reagents, which highlights the generality and robustness of this methodology.     

Pd‐Catalyzed Selective Bifunctionalization of 3‐Iodo‐o‐Carborane by Pd Migration

A palladium‐catalyzed highly selective 3,4‐bifunctionalization of 3‐I‐o‐carborane has been developed, leading to the preparation of 3‐alkenyl‐4‐R‐o‐carboranes (R=alkyl, alkynyl, aryl, allyl, CN, and amido) in high to excellent yields. This protocol combines the sequential activation of cage B(3)?I and B(4)?H bonds by Pd migration from exo‐alkenyl sp² C to cage B(4), which is driven by thermodynamic force. This represents a brand‐new strategy for selective bifunctionalization of carboranes with two different substituents.     

Iridium‐Catalyzed Synthesis of Diaryl Ethers by Means of Chemoselective CF Bond Activation and the Formation of BF Bonds

Transition‐metal‐catalyzed C? F activation, in comparison with C? H activation, is more difficult to achieve and therefore less fully understood, mainly because carbon–fluorine bonds are the strongest known single bonds to carbon and have been very difficult to cleave. Transition‐metal complexes are often more effective at cleaving stronger bonds, such as C(sp²)? X versus C(sp³)? X. Here, the iridium‐catalyzed C? F activation of fluorarenes was achieved through the use of bis(pinacolato)diboron with the formation of the B? F bond and self‐coupling. This strategy provides a convenient method with which to convert fluoride aromatic compounds into symmetrical diaryl ether compounds. Moreover, the chemoselective products of the C? F bond cleavage were obtained at high yields with the C? Br and C? Cl bonds remaining.     

Synthesis of Homoallylic Alcohols with Acyclic Quaternary Centers through CoIII‐Catalyzed Three‐Component C−H Bond Addition to Internally Substituted Dienes and Carbonyls

An efficient Co^III‐catalyzed three‐component strategy to prepare homoallylic alcohols containing acyclic quaternary centers is disclosed. This transformation enables the introduction of two C?C σ bonds through C?H bond activation and sequential addition to internally substituted dienes and a wide range of aldehydes and activated ketones. Isoprene and other internally monosubstituted dienes are effective inputs, with the reaction proceeding with high diastereoselectivity for those substrate combinations that result in more than one stereogenic center. Moreover, the opposite relative stereochemistry can be achieved by employing 1,2‐disubstituted dienes. A mechanism for the transformation is proposed based upon the relative stereochemistry of the products and studies with isotopically labeled starting materials.     

Cooperative Lewis Acid/Cp*CoIII Catalyzed C−H Bond Activation for the Synthesis of Isoquinolin‐3‐ones

A facile route toward the synthesis of isoquinolin‐3‐ones through a cooperative B(C₆F₅)₃‐ and Cp*Co^III‐catalyzed C?H bond activation of imines with diazo compounds is presented. The inclusion of a catalytic amount of B(C₆F₅)₃ results in a highly efficient reaction, thus enabling unstable NH imines to serve as substrates.     

Iridium‐Catalyzed β‐Alkynylation of Aliphatic Oximes as Masked Carbonyl Compounds and Alcohols

An Ir‐catalyzed C(sp³)?H alkynylation of aliphatic ketones, aldehydes, and alcohols was achieved by using the corresponding oxime derivatives and a Ir^III catalyst. This general reaction is selective towards primary C(sp³)?H bonds and can be used for the late‐stage C?H alkynylation of complex molecules.     

Rhodium(I)‐Catalyzed Sequential C(sp)?C(sp3) and C(sp3)?C(sp3) Bond Formation through Migratory Carbene Insertion

A Rh^I‐catalyzed three‐component reaction of tert‐propargyl alcohol, diazoester, and alkyl halide has been developed. This reaction can be considered as a carbene‐involving sequential alkyl and alkynyl coupling, in which C(sp) C(sp³) and C(sp³) C(sp³) bonds are built successively on the carbenic carbon atom. The Rh^I‐carbene migratory insertion of an alkynyl moiety and subsequent alkylation are proposed to account for the two separate C C bond formations. This reaction provides an efficient and tunable method for the construction of all‐carbon quaternary center.     

Nickel‐Catalyzed Alkoxy–Alkyl Interconversion with Alkylborane Reagents through C−O Bond Activation of Aryl and Enol Ethers

A nickel‐catalyzed alkylation of polycyclic aromatic methyl ethers as well as methyl enol ethers with B‐alkyl 9‐BBN and trialkylborane reagents that involves the cleavage of stable C(sp²)?OMe bonds is described. The transformation has a wide substrate scope and good chemoselectivity profile while proceeding under mild reaction conditions; it provides a versatile way to form C(sp²)?C(sp³) bonds that does not suffer from β‐hydride elimination. Furthermore, a selective and sequential alkylation process by cleavage of inert C?O bonds is presented to demonstrate the advantage of this method.     

Group 9 Metal Complexes of meso‐Aryl‐Substituted Rubyrin

The metalation of meso‐tetrakis(pentafluorophenyl)‐substituted [26]rubyrin has been explored with Group 9 metal salts (Rh^I, Co^II, Ir^III), affording a Hückel aromatic [26]rubyrin–bis‐Rh^I complex with a highly curved gable‐like structure, a Hückel antiaromatic [24]rubyrin–bis‐Co^II complex that displays intramolecular antiferromagnetic coupling between the two Co^II ions (J=?4.5 cm^?1), and two Cp*‐capped Ir^III complexes; in one, the iridium metal sits on the [26]rubyrin frame with two Ir?N bonds, whereas the other has an additional Ir?C bond, although both Ir^III complexes display moderate aromatic character. This work demonstrates characteristic metalation abilities of this [26]rubyrin toward Group 9 metals.     

Surface oxidation process of a diamond‐like carbon film analyzed by difference X‐ray photoelectron spectroscopy

Difference X‐ray photoelectron spectroscopy (D‐XPS) revealed the surface oxidation process of a diamond‐like carbon (DLC) film. Evaluation of surface functional groups on DLC solely by the C 1s spectrum is difficult because the spectrum is broad and has a secondary asymmetric lineshape. D‐XPS clarified the subtle but critical changes at the DLC surface caused by wet oxidation. The hydroxyl (C―OH) group was dominant at the oxidized surface. Further oxidized carbonyl (C?O) and carboxyl (including carboxylate) (COO) groups were also obtained; however, the oxidation of C?O to COO was suppressed to some extent because the reaction required C―C bond cleavage. Wet oxidation cleaved the aliphatic hydrogenated and non‐hydrogenated sp² carbon bonds (C―H sp² and C―C sp²) to create a pair of C―OH and hydrogenated sp³ carbon (C―H sp³) bonds. The reaction yield for C―H sp² was superior at the surface, suggesting that the DLC film was hydrogen rich at the surface. Oxidation of aromatic sp² rings or polycyclic aromatic hydrocarbons such as nanographite to phenols did not occur because of their resonance stabilization with electron delocalization. Non‐hydrogenated sp³ carbon (C―C sp³) bonds were not affected by oxidation, suggesting that these bonds are chemically inert. Copyright © 2014 John Wiley & Sons, Ltd.     

Cu‐Catalyzed Intramolecular Amidation of Unactivated C(sp3)−H Bonds To Synthesize N‐Substituted Indolines

A copper‐catalyzed intramolecular amidation of unactivated C(sp³)?H bonds to construct indoline derivatives has been developed. Such an amidation proceeded well at primary C?H bonds preferred to secondary C?H bonds. The transformation owned a broad substrate scope. The corresponding indolines were obtained in good to excellent yields. N‐Formal and other carbonyl groups were suitable and were easily deprotected and transformed into methyl or long‐chained alkyl groups. Preliminary mechanistic studies suggested a radical pathway.