Copper-Catalyzed Intramolecular C(sp3)H and C(sp2)H Amidation by Oxidative Cyclization

Copper-promoted site-selective carbonylation of sp3 and sp2 C-H bonds with nitromethane

Copper-promoted direct carbonylation of unactivated sp3 C-H and aromatic sp2 C-H bonds of amides was developed using nitromethane as a novel carbonyl source. The sp3 C-H functionalization showed high site-selectivity by favoring the C-H bonds of α-methyl groups. The sp2 C-H carbonylation featured high regioselectivity and good functional group compatibility. Kinetic isotope effect studies indicated that the sp3 C-H bond breaking step is reversible, whereas the sp2 C-H bond cleavage is an irreversible but not the rate-determining step. Control experiments showed that a nitromethyl intermediate should be involved in the present reaction.

Copper-catalyzed oxidative C-H/C-H cross-coupling of benzamides and thiophenes

A copper-catalyzed oxidative C-H/C-H cross-coupling of benzamides and thiophenes has been developed. This reaction exhibits a broad substrate scope and excellent tolerance of functional groups. The directing group could be readily removed to afford 2-thienylbenzoic acids.

Cu-Catalyzed Intramolecular Amidation of Unactivated C(sp(3) )-H Bonds To Synthesize N-Substituted Indolines

A copper-catalyzed intramolecular amidation of unactivated C(sp(3) )-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.

Recent advances in copper-mediated chelation-assisted functionalization of unactivated C–H bonds

Recent advances in copper-mediated (both stoichiometric and catalytic) chelation-assisted functionalization of unactivated C–H bonds are reviewed.

Divergent copper-mediated dimerization and hydroxylation of benzamides involving C–H bond functionalization

Copper-mediated C–H activation of aminoquinoline benzamides to give either hydroxylation or dimerization compounds were investigated.

Copper-catalyzed oxidative carbon–heteroatom bond formation: a recent update

This review updates recent advances in Cu-catalyzed (anaerobic) oxidative carbon–heteroatom bond formation on sp³- and sp²-C–H bonds as well as alkenes, classified according to the types of stoichiometric oxidants.

Highly mono-selective ortho-trifluoromethylation of benzamides via 8-aminoquinoline assisted Cu-promoted C–H activations

A highly mono-selective ortho-trifluoromethylation of benzamides was achieved via Cu-promoted C–H activations employing an 8-aminoquinoline group as the bidentate directing group and Togni reagent II as the CF₃ source.

Annulation based on 8-aminoquinoline assisted C–H activation: an emerging tool in N-heterocycle construction

As an important emerging area of 8-aminoquinoline assisted C–H activation, the construction of heterocycles via direct C–H activation and domino reactions involving domino C–H activation/annulation has been highlighted.

Copper-catalyzed intermolecular amidation of 8-methylquinolines with N-fluoroarylsulfonimides via Csp3–H activation

An efficient Cu-catalyzed intermolecular amidation of 8-methylquinolines with N-fluoroarylsulfonimides via Csp³–H activation has been developed.

Cobalt-promoted selective arylation of benzamides and acrylamides with arylboronic acids

A novel cobalt-promoted arylation of aryl C–H bonds with arylboronic acids has been realized by using 8-aminoquinoline as the directing group. A notable feature of this newly developed protocol is that acrylamides, which cannot be arylated using copper salts as the promoter, can also be efficiently arylated.

Unprecedented copper-mediated oxidative demethylation of propionamides via bidentate-chelation assistance

The copper-mediated bidentate-chelation directing group assisted oxidative demethylation of substituted propionamides was developed for the first time.

Recent advances in copper-catalyzed C-H bond amidation

Copper catalysis has been known as a powerful tool for its ubiquitous application in organic synthesis. One of the fundamental utilities of copper catalysis is in the C–N bond formation by using carbon sources and nitrogen functional groups such as amides. In this review, the recent progress in the amidation reactions employing copper-catalyzed C–H amidation is summarized.

Pyridine-enabled copper-promoted cross dehydrogenative coupling of C(sp2)-H and unactivated C(sp3)-H bonds

The pyridine-enabled cross dehydrogenative coupling of sp2 C-H bonds of polyfluoroarenes and unactivated sp3 C-H bonds of amides was achieved via a copper-promoted process with good functional group compatibility. This reaction showed great site-selectivity by favoring the sp2 C-H bonds ortho to two fluoro atoms of arenes and the sp3 C-H bonds of α-methyl groups over those of the α-methylene, β- or γ-methyl groups of the aliphatic amides. Mechanistic studies revealed that sp3 C-H bond cleavage is an irreversible but not the rate-determining step, and the sp2 C-H functionalization of arenes appears precedent to the sp3 C-H functionalization of amides in this process.

Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization

Cyclopropenimine superbases were employed to catalyze the ring-opening polymerization of lactide. Polymerization occurred readily in the presence and absence of alcohol initiators. Polymerizations in the absence of alcohol initiators revealed a competitive initiation mechanism involving deprotonation of lactide by the cyclopropenimine to generate an enolate. NMR and MALDI-TOF analysis of the poly(lactides) generated from cyclopropenimines in the absence of alcohol initiators showed acylated lactide and hydroxyl endgroups. Model studies and comparative experiments with guanidine and phosphazene catalysts revealed the subtle influence of the nature of the superbase on competitive initiation processes.

Cu(II)-Mediated C(sp(2))-H Hydroxylation

A Cu(II)-mediated ortho-C-H hydroxylation using a removable directing group has been developed. The reaction exhibits considerable functional group tolerance. The use of O2 as an oxidant is crucial for the reactivity. Water is also found to significantly improve this reaction.

Copper-Catalyzed Formal [4 + 1] Cycloaddition of Benzamides and Isonitriles via Directed C-H Cleavage

A copper-catalyzed formal [4 + 1] cycloaddition of benzamides and isonitriles via 8-aminoquinoline-directed C-H cleavage has been developed. The reaction proceeds well even in the presence of a base metal catalyst, CuBr·SMe2, alone to deliver the corresponding 3-iminoisoindolinones in good yields. Moreover, the unique acceleration effects of diphenyl sulfide are also disclosed.

Copper-Catalyzed Aerobic Oxidations of Organic Molecules: Pathways for Two-Electron Oxidation with a Four-Electron Oxidant and a One-Electron Redox-Active Catalyst

Selective oxidation reactions have extraordinary value in organic chemistry, ranging from the conversion of petrochemical feedstocks into industrial chemicals and polymer precursors to the introduction of heteroatom functional groups into pharmaceutical and agrochemical intermediates. Molecular oxygen (O2) would be the ideal oxidant for these transformations. Whereas many commodity-scale oxidations of simple hydrocarbon feedstocks employ O2 as an oxidant, methods for selective oxidation of more complex molecules bearing diverse functional groups are often incompatible with existing aerobic oxidation methods. The latter limitation provides the basis for our interest in the development of new catalytic transformations and the elucidation of mechanistic principles that underlie selective aerobic oxidation reactions. One challenge inherent in such methods is the incommensurate redox stoichiometry associated with the use of O2, a four-electron oxidant, in reactions that achieve two-electron oxidation of organic molecules. This issue is further complicated by the use of first-row transition-metal catalysts, which tend to undergo facile one-electron redox steps. In recent years, we have been investigating Cu-catalyzed aerobic oxidation reactions wherein the complexities just noted are clearly evident. This Account surveys our work in this area, which has emphasized three general classes of reactions: (1) single-electron-transfer reactions for oxidative functionalization of electron-rich substrates, such as arenes and heterocycles; (2) oxidative carbon-heteroatom bond-forming reactions, including C-H oxidations, that proceed via organocopper(III) intermediates; and (3) methods for aerobic oxidation of alcohols and amines that use Cu(II) in combination with an organic redox-active cocatalyst to dehydrogenate the carbon-heteroatom bond. These reaction classes demonstrate three different pathways to achieve two-electron oxidation of organic molecules via the cooperative involvement of two one-electron oxidants, either two Cu(II) species or Cu(II) and a nitroxyl cocatalyst. They show the ability of Cu to participate in traditional organometallic steps commonly associated with precious-metal catalysts, such as C-H activation and reductive elimination, but also demonstrate the accessibility of reaction steps not typically associated with precious-metal catalysts, such as single-electron transfer. Many of the Cu-catalyzed reactions offer advantages over analogous two-electron oxidation reactions mediated by palladium or other noble metals. For example, carbon-heteroatom oxidative coupling reactions in the first two reaction classes noted above are capable of using O2 as the terminal oxidant, while analogous reactions with Pd commonly require less desirable oxidants, such as hypervalent iodine or electrophilic halogen sources. In addition, the alcohol and amine oxidations in the third reaction class are significantly more efficient and show much broader scope and functional group tolerance than related Pd-catalyzed reactions. The mechanistic basis for these differences are described herein.