Transition metal-catalyzed arylation of unactivated C(sp3)-H bonds

Nickel-catalyzed chelation-assisted direct arylation of unactivated C(sp3)–H bonds with aryl halides

The nickel-catalyzed chelation-assisted unactivated β-C(sp³)–H bond arylation of aliphatic acid derivatives with aryl iodides/bromides has been achieved.

Sunlight photocatalyzed regioselective β-alkylation and acylation of cyclopentanones

Visible light induced direct β-C–H/C–C conversion of cyclopentanones was accomplished by using tetrabutylammonium decatungstate, TBADT, as the photocatalyst.

Nickel or phenanthroline mediated intramolecular arylation of sp3 C-H bonds using aryl halides

The development of the intramolecular arylation of sp(3) C-H bonds adjacent to nitrogen using aryl halides is described. Arylation was accomplished using either Ni(COD)2 or 1,10-phenanthroline in substoichiometric amounts, and the reaction conditions were applied to a variety of electronically differentiated benzamide substrates. Preliminary studies suggest a mechanism involving aryl and alkyl radical intermediates.

To be or not to be metal-free: trends and advances in coupling chemistries

Coupling reactions have been part of several extensive studies in order to develop innovative and greener protocols that can generate a wide range of compounds with applications in pharmaceuticals, agrochemicals and biologically active compounds. Metal-free couplings are an important and increasingly trendy field that has attracted a significant deal of interest in recent years, generating a lot of controversy on the issue of whether metal free is really free. Aside from focusing on such a controversial topic itself, this contribution aims to provide a brief introduction on coupling chemistry to point out the transition of this technology from metal-catalyzed to metal-free. This is followed by a range of key selected synthetically useful metal-free processes and a brief commentary on the current debate of whether metal-free reactions are really metal-free and the required experiments for a full understanding of a metal-free coupling process.

An easy direct arylation of 5-pyrazolones

A mild, efficient and catalytic ligand-free method for the direct arylation of 5-pyrazolones by Pd-catalyzed C-H bond activation is reported. The process smoothly proceeds and yields are moderate to excellent.

An efficient palladium-catalyzed C-H alkoxylation of unactivated methylene and methyl groups with cyclic hypervalent iodine (i(3+) ) oxidants

All the hype: The title reaction has been developed for the facile synthesis of a variety of complex alkyl ethers. Cyclic hypervalent iodine (I(3+) ) reagents serve as oxidants for this unique CH alkoxylation reaction. The reaction demonstrates excellent reactivity, good functional-group tolerance, and high yields. Q=8-aminoquinoline-derived auxiliary.

Catalytic functionalization of C(sp2)-H and C(sp3)-H bonds by using bidentate directing groups

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.

Palladium-catalyzed through-space C(sp(3))-H and C(sp(2))-H bond activation by 1,4-palladium migration: efficient synthesis of [3,4]-fused oxindoles

Palladium two step: Linear anilides were converted into the title compounds in good to excellent yields through a palladium-catalyzed domino carbopalladation/1,4-palladium shift sequence. The C(sp(3) )-H activation involves a seven-membered palladacycle, and is chemoselective in the presence of competitive C(sp(2) )H bonds. DMA=N,N-dimethylacetamide, OPiv=pivalate.

Transition metal-catalyzed C(vinyl)-C(vinyl) bond formation via double C(vinyl)-H bond activation

Transition metal-catalyzed oxidative dehydrogenative coupling reactions of Caryl-H bonds with Cvinyl-H bonds to generate a Caryl-Cvinyl bonds have been well developed in recent decades. However, only a few studies have focused on the direct Cvinyl-Cvinyl bond formation via double Cvinyl-H bond activation. Recent developments in this active area have been highlighted in this tutorial review.

Palladium-catalyzed direct C-H arylation of cyclic enaminones with aryl iodides

A ligand-free method for the Pd-catalyzed direct arylation of cyclic enaminones using aryl iodides was developed. This method can be applied to a wide range of cyclic enaminones and aryl iodides with excellent C5-regioselectivity. Using widely available aryl iodides, the generality of this transformation provides easy access to a variety of 3-arylpiperidine structural motifs.