Challenges in C–C bond formation through direct transformations of sp2 C–H bonds

Thianthrenium-Enabled Phosphorylation of Aryl C-H Bonds via Electron Donor-Acceptor Complex Photoactivation

An efficient strategy for the preparation of aryl phosphonates via blue-light-promoted single electron transfer process of an EDA complex between phosphites and thianthrenium salts has been demonstrated. The corresponding substituted aryl phosphonates were obtained in good to excellent yields, and the byproduct thianthrene can be recovered and reused in quantity. This developed method realizes the construction of aryl phosphonates through the indirect C-H functionalization of arenes, which has potential application value in drug discovery and development.

Palladium-catalyzed direct C2-arylation of azoles with aromatic triazenes

A highly efficient palladium-catalyzed arylation of azoles at the C2-position using 1-aryltriazenes as aryl reagents was developed. Azoles including oxazoles, thiazoles, imidazoles, 1,3,4-oxadiazoles, and oxazolines could react with 1-aryltriazenes smoothly to generate the corresponding products in good to excellent yields, and various substitution patterns were tolerated toward the reaction.

Palladium-Catalyzed Direct Arylation of Polyfluoroarenes for Accessing Tetra- ortho-Substituted Biaryls: Buchwald-type Ligand Having Complementary -PPh2 Moiety Exhibits Better Efficiency

The first general examples of direct C-H arylation of electron-deficient polyfluoroarenes with challenging di- ortho-substituted aryl(heteroaryl) chlorides for tetra- ortho-substituted biaryl synthesis are reported. Key to success is the use of Buchwald-type biaryl phosphine ligand, notably with inexpensive -PPh₂ moiety (instead of -PCy₂ group). Pd(OAc)₂ associated with ligand L9 exhibits even higher efficiency than the corresponding SPhos toward this reaction. A wide range of sterically hindered di- ortho-substituted chloroarenes bearing electron-donating or -withdrawing groups are found applicable. Excellent product yields are obtained under mild reaction conditions, and the catalyst loading down to 0.25 mol % of Pd can also be achieved.

Mixing O-Containing and N-Containing Directing Groups for C-H Activation: A Strategy for the Synthesis of Highly Functionalized 2,2'-Biaryls

A strategy combining O- and N-containing directing groups has been developed for the synthesis of 2,2'-biaryl via Pd-mediated C-H bond activation and oxidative coupling. This new transformation may proceed through a mechanism involving Pd(II) and Pd(IV) intermediates. We found the use of PTSA and HFIP to be critical for the reaction and suggest that these reagents could serve as efficient ligands for this C-C bond formation. This methodology provides broad functional group tolerance, excellent reactivity, and high yields.

Transition metal free regio-selective C–H hydroxylation of chromanones towards the synthesis of hydroxyl-chromanones using PhI(OAc)2 as the oxidant

Herein, we report a highly efficient PhI(OAc)₂ mediated regioselective, direct C–H hydroxylation of chromanones.

The use of carboxylic acids as traceless directing groups for regioselective C–H bond functionalisation

This feature article focuses on the use of carboxylic acids as traceless directing groups and the application of this concept to achieve regiochemical control in organic chemistry.

N-Heterocyclic carbene–palladium(ii)–1-methylimidazole complex catalyzed direct C–H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides

NHC–Pd(ii) complex catalyzed C–H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides was reported.

Palladium-Catalyzed C-H Arylation of (Benzo)oxazoles or (Benzo)thiazoles with Aryltrimethylammonium Triflates

The C-H arylation of (benzo)oxazoles or (benzo)thiazoles with aryltrimethylammonium triflates was carried out via Pd-catalyzed C-H/C-N cleavage. Oxazoles, thiazoles, benzoxazole, and benzothiazole were arylated using activated and deactivated aryltrimethylammonium triflates to give 2-aryl(benzo)oxazoles or 2-aryl(benzo)thiazoles in reasonable to excellent yields.

Intramolecular cross dehydrogenative coupling of 4-substituted coumarins: rapid and efficient access to coumestans and indole[3,2-c]coumarins

A palladium-catalyzed highly efficient and atom-economical intramolecular cross dehydrogenative coupling (CDC) reaction to access fused polyheterocycles containing a coumarin nucleus has been developed.

Regioselectivity in palladium-catalysed direct arylation of 5-membered ring heteroaromatics

In the past few years, several results using modified catalysts and new reaction conditions have been reported permitting better control of the regioselectivity of Pd-catalysed arylations.

Direct C–H heteroarylation of azoles with 1,2-di(pyrimidin-2-yl)disulfides through C–S cleavage of disulfides

C–C bond construction via C–H bond functionalization of oxazoles/thiazoles and C–S bond cleavage of di(hetero)aryl disulfides are described.

Ruthenium-catalyzed C-H activation of thioxanthones

Thioxanthones - being readily available in one step from thiosalicylic acid and arenes - were used in ruthenium-catalyzed C-H-activation reaction to produce 1-mono- or 1,8-disubstituted thioxanthones in good to excellent yields. Scope and limitation of this reaction are presented.

Metal-free oxidative decarbonylative coupling of aromatic aldehydes with arenes: direct access to biaryls

A metal-free oxidative decarbonylative coupling of aromatic aldehydes with electron-rich or electron-deficient arenes to produce biaryl compounds was developed. This novel coupling was proposed to proceed via a non-chain radical homolytic aromatic substitution (HAS) type mechanism, based on the substrate scope, ortho-regioselectivity, radical trapping experiments and DFT calculation studies. With the ready availability of aromatic aldehydes and arenes, metal-free conditions should make this coupling attractive for the biaryl synthesis.

Ru-catalysed C-H arylation of indoles and pyrroles with boronic acids: scope and mechanistic studies

The Ru-catalysed C2–H arylation of indoles and pyrroles by using boronic acids under oxidative conditions is reported. This reaction can be applied to tryptophan derivatives and tolerates a wide range of functional groups on both coupling partners, including bromides and iodides, which can be further derivatised selectively. New indole-based ruthenacyclic complexes are described and investigated as possible intermediates in the reaction. Mechanistic studies suggest the on-cycle intermediates do not possess a para-cymene ligand and that the on-cycle metalation occurs through an electrophilic attack by the Ru centre.

Conditions for palladium-catalyzed direct arylations of 4-bromo and 4-iodo N-substituted pyrazoles without C–Br or C–I bond cleavage

The Pd-catalyzed arylation at the C5 position ofN-protected pyrazole derivatives bearing bromo or iodo substituents at the C4 position is described.

Ruthenium- and palladium-catalyzed consecutive coupling and cyclization of aromatic sulfoximines with phenylboronic acids: an efficient route to dibenzothiazines

A ruthenium-catalyzed ortho arylation of aromatic sulfoximines with aromatic boronic acids followed by intramolecular cyclization in the presence of a palladium catalyst providing dibenzothiazines is described.

Chromium-catalyzed transformations with Grignard reagents – new opportunities for cross-coupling reactions

Recent advances in chromium-catalyzed cross-couplings of C–X and C–H bonds with Grignard reagents are highlighted.

Direct amidation of the phenylalanine moiety in short peptides via Pd-catalyzed C–H activation/C–N formation

The direct amidation of dipeptides through direct aryl C–H transformation of the phenylalanine residue via Pd catalysis.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

Chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized N-heterocyclic carbenes: synthesis, structure, and catalytic activity towards C–H activation

Chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized NHCs were synthesized, characterized and tested for C–H activation of (benzo)oxazoles.

Synthesis of heteroarenes dyads from heteroarenes and heteroarylsulfonyl chlorides via Pd-catalyzed desulfitative C–H bond heteroarylations

We report palladium-catalyzed synthesis of heteroarenes dyads using heteroarylsulfonyl chlorides as coupling partners. The C–H bond functionalizations occurred at α-position with pyrroles and furans, while at β-position with thiophenes.