Nickel-Catalyzed Cross-Dehydrogenative Coupling of α-C(sp3)-H Bonds in N-Methylamides with C(sp3)-H Bonds in Cyclic Alkanes

One-Pot Oxidative Amidation of Aldehydes via the Generation of Nitrile Imine Intermediates

A one-pot procedure for the oxidative amidation of aldehydes via the in situ generation of reactive nitrile imine (NI) intermediates has been developed. Distinct from our progenitor processes, mechanistic and control experiments revealed that the NI undergoes rapid oxidation to an acyl diazene species, which then facilitates N-acylation of an amine. A range of substrates have been explored, including application in the synthesis of pharmaceutically relevant compounds.

Transition metal-free C(sp3)-H selenation of β-ketosulfones

The installation of selenium groups has become an essential step across a number of industries such as agrochemicals, drug discovery, and materials. However, direct C(sp3)-H selenation, which is most atom economical, remains a formidable challenge, and only a few examples have been reported to date. In this article, we introduce the transition metal-free C(sp3)-H selenation with the easily available β-ketosulfones and diselenides as the material source. This benign protocol permits access to a broad spectrum of α-aryl(alkyl) seleno-β-ketosulfones in high yields with outstanding functional group compatibility. Distinct advantages of this protocol over all previous methods encompass the utilization of base and air as an oxidant, room temperature, and enhanced green chemistry matrices.

The Recent Advances in Iron-Catalyzed C(sp3 )-H Functionalization

The use of iron as a core metal in catalysis has become a research topic of interest over the last few decades. The reasons are clear. Iron is the most abundant transition metal on Earth's crust and it is widely distributed across the world. It has been extracted and processed since the dawn of civilization. All these features render iron a noncontaminant, biocompatible, nontoxic, and inexpensive metal and therefore it constitutes the perfect candidate to replace noble metals (rhodium, palladium, platinum, iridium, etc.). Moreover, direct C-H functionalization is one of the most efficient strategies by which to introduce new functional groups into small organic molecules. The majority of organic compounds contain C(sp3 )-H bonds. Given the enormous importance of organic molecules in so many aspects of existence, the utilization and bioactivity of C(sp3 )-H bonds are of the utmost importance. This review sheds light on the substrate scope, selectivity, benefits, and limitations of iron catalysts for direct C(sp3 )-H bond activations. An overview of the use of iron catalysis in C(sp3 )-H activation protocols is summarized herein up to 2022.

Oxidative Cross Dehydrogenative Coupling of N-Heterocycles with Aldehydes through C(sp3)-H Functionalization

Existing methodologies for metal-catalyzed cross-couplings typically rely on preinstallation of reactive functional groups on both reaction partners. In contrast, C-H functionalization approaches offer promise in simplification of the requisite substrates; however, challenges from low reactivity and similar reactivity of various C-H bonds introduce considerable complexity. Herein, the oxidative cross dehydrogenative coupling of α-amino C(sp3)-H bonds and aldehydes to produce ketone derivatives is described using an unusual reaction medium that incorporates the simultaneous use of di-tert-butyl peroxide as an oxidant and zinc metal as a reductant. The method proceeds with a broad substrate scope, representing an attractive approach for accessing α-amino ketones through the formal acylation of C-H bonds α to nitrogen in N-heterocycles. A combination of experimental investigation and computational modeling provides evidence for a mechanistic pathway involving cross-selective nickel-mediated cross-coupling of α-amino radicals and acyl radicals.

TBAI-Catalyzed Oxidative Coupling of Benzyl Ketones to Synthesize 2,3-Diaryl-1,4-Diketones in Water

An efficient and green route of C-C bond formation was disclosed to construct 2,3-diaryl-1,4-diketones from α-methylene ketones by the catalysis of tetrabutylammonium iodide (TBAI) with tert-butyl hydroperoxide (TBHP) as an oxidant in water. This reaction affords the desired products in good to excellent yields from readily available materials, with a broad substrate scope, good functional group tolerance, and mild reaction conditions. Furthermore, tetrasubstituted furan and pyrrole were smoothly constructed from α-methylene ketones in one pot with 96 and 90% yields, respectively.

Transition-Metal-Free C(sp3)-H Coupling of Cycloalkanes Enabled by Single-Electron Transfer and Hydrogen Atom Transfer

Here we report a unique transition-metal-free C(sp³)-H/C(sp³)-H coupling of cycloalkanes at room temperature. Unactivated cycloalkanes and 2-azaallyls underwent the combination process of single-electron transfer (SET) and hydrogen atom transfer (HAT) to deliver a wide variety of cycloalkane-functionalized products. This expedient approach enables C(sp³)-H/C(sp³)-H coupling of cycloalkanes under mild conditions without transition metals, initiators, and oxidants.

Copper-Catalyzed Alkylarylation of Unactivated Alkenes: Synthesis of 3-Alkyl Indolines from N-Allyl Anilines and Alkanes

A rare example of C(sp³ )-H functionalization of simple alkanes with unactivated alkenes is presented. In the presence of a copper salt and di-tert-butyl peroxide (DTBP), N-allyl anilines underwent exo-selective alkylation/cyclization cascade with unactivated alkenic bonds as radical acceptors and simple alkanes as radical precursors, providing a direct access to 3-alkyl indolines. The present protocol features simple operation, broad substrate scope and great exo selectivity.

Nickel-catalyzed regioselective C–H acylation of chelating arenes: a new catalytic system for C–C bond formation via a radical process and its mechanistic explorations

An unprecedented acylation at the ortho C–H bond of chelating arenes via the Ni(ii)-catalyzed cross dehydrogenative coupling strategy has been developed here.

Nickel-catalyzed regioselective C–H halogenation of electron-deficient arenes

A straightforward Ni(ii)-catalyzed general strategy was developed for the ortho-halogenation of electron-deficient arenes with easily available halogenating reagents N-halosuccinimides (NXS; X = Br, Cl and I).

Nickel-catalyzed C–H bond trifluoromethylation of 8-aminoquinoline derivatives by acyl-directed functionalization

A Ni(TFA)₂-catalyzed ortho-trifluoromethylation of 8-aminoquinoline derivatives was developed by C–H bond acyl-directed functionalization.

Cobalt catalyzed regioselective C–H methylation/acetoxylation of anilides: new routes for C–C and C–O bond formation

The first cobalt-catalyzed regioselective C–H methylation/acetoxylation reactions of anilides using peroxides and acetic acid respectively as attacking reagents have been developed herein.