Functionalizations of Aryl CH Bonds in 2-Arylpyridines via Sequential Borylation and Copper Catalysis

2-Pyridone-Directed CuII-Catalyzed General Method of C(sp2)-H Activation for C-S, C-Se, and C-N Cross-Coupling: Easy Access to Aryl Thioethers, Selenide Ethers, and Sulfonamides and DFT Study

We have demonstrated N-substituted 2-pyridones as an N,O-directing group for selective C(sp2)-H-activated thiolation, selenylation, and sulfonamidation of ortho C-H bonds of benzamides. This method utilizes a cost-effective Cu(II)-salt catalyst instead of precious metal catalysts, achieving high yields, including gram-scale synthesis and excellent functional group tolerance. We applied this protocol to access 30 different compounds with high yields, demonstrating thiolation of fluorine-substituted benzamides as well. Density functional theory (DFT) calculations support the mechanism, including acetate-supported concerted metalation deprotonation (CMD) steps and the unique role of dimethyl sulfoxide (DMSO) solvent. The facile synthesis of pharmaceutically important sulfonamides and other compounds highlights the method's potential in chemistry and medicinal chemistry.

Boron-Mediated Regioselective Aromatic C-H Functionalization via an Aryl BF2 Complex

An efficient regioselective functionalization of 2-aryl-heteroarenes and aryl aldehydes via an azaaryl BF₂ complex has been developed. Mechanistically the reaction comprises fluoride to bromide ligand exchange on an aryl boron species and consecutive C-B bond cleavage to deliver a broad range of functionalized products. The reaction is high yielding, has a broad substrate scope where several different heteroarenes can be functionalized with chloro, bromo, iodo, hydroxyl, amine and BF₂ in a highly regioselective fashion. The method can be applied for late-stage functionalization or for rapid skeleton remodeling with for instance cross-couplings.

Bottom-Up Synthesis of Multiply Fused PdII Anthriporphyrinoids

Anthriporphyrinoid and its dimeric homologues were synthesized by Suzuki-Miyaura coupling and subsequent oxidation. Both porphyrinoids were smoothly converted to their Pd^II complexes and were further decorated by Suzuki-Miyaura coupling with thiophene derivatives and subsequent oxidative fusion reaction to provide multiply fused compounds. Most Pd^II anthriporphyrinoids have been structurally well characterized to be planar for monomeric and helically twisted for dimeric species. The dimeric anthriporphyrinoids show paratropic ring currents due to their global antiaromatic networks, the extent of which increases with an increase of conjugated network. Multiply fused dimeric anthriporphyrinoids show helical structures, fully reversible six redox potentials, small HOMO-LUMO gaps, and absorption tails reaching in the near-infrared region, suggesting the high potential of this approach to explore molecular graphene. Optical separations of the dimeric helical species were accomplished, and racemization barrier heights were determined.

Copper-catalyzed oxidative functionalization of benzylic C–H bonds with quinazoline 3-oxides

A highly efficient copper-catalyzed oxidative functionalization of benzylic C(sp³)–H bonds with quinazoline 3-oxides has been developed.

Regioselectivity in C-H activation: reagent control in cyclometallation of 2-(1-naphthyl)-pyridine

2-(1-Naphthyl)-pyridine () possesses sp(2) C-H bonds in both the γ- and δ-positions and is therefore a suitable substrate for studying the cyclometallation selectivity with different reagents and conditions. Such selectivity studies are reported. Based on deuterium-exchange experiments it is concluded that cycloruthenation with RuCl2(p-cymene) dimer is reversible with kinetic and thermodynamic preference for γ-substitution. Electrophilic cycloborylation, on the other hand, shows unusual δ-substitution. The previously published cyclopalladation and cycloauration of the substrate was studied in detail and was shown to be irreversible; they proceed under kinetic control and give γ- and δ-substitution for palladium and gold, respectively.

Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance

In a series of regioisomeric [Ir(C^N)₂(bpy)]⁺ complexes containing methylsulfonyl groups on the cyclometallating ligands, the influence of the substitution position on photophysical, electrochemical and LEC device properties is investigated.

Luminescent organoboron ladder compounds via directed electrophilic aromatic C–H borylation

Regioselective electrophilic borylation of a pyridyl-flanked fluorene provides highly luminescent, air-stable boron-bridged ladder species.

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.

Cu(II)-catalyzed coupling of aromatic C-H bonds with malonates

A new Cu(II)-catalyzed oxidative coupling of arenes with malonates has been developed using an amide-oxazoline directing group. The reaction proceeds via C(sp(2))-H activation and malonate coupling, followed by intramolecular oxidative N-C bond formation. A variety of arenes bearing different substituents are shown to be compatible with this reaction.

Guanidinium iodide-catalyzed oxidative α-nitroalkylation of β-ketoamides

Oxidative nitroalkylation of β-ketoamides and nitroalkanes, mediated by hypoiodide generated from tert-butyl hydrogen peroxide and a catalytic amount of guanidinium iodide, afforded the corresponding α-nitroalkyl-β-ketoamides in up to 97% yield.

The development of carbene-stabilized N–O radical coupling strategy in metal-free regioselective C–H azidation of quinoline N-oxides

The key regioselective issue of quinoline N-oxide azidation was resolved via the oxidative cross-coupling of carbene-stabilized N–O radicals and TMSN₃. Compared with the reported azidations, the present metal-free procedure is convenient and regioselective under mild conditions, and could be scaled up to gram-synthesis.

Metal-free oxidative C(sp3)–H bond functionalization of alkanes and alkylation-initiated radical 1,2-aryl migration in α,α-diaryl allylic alcohols

A C(sp³)–H bond functionalization of alkanes and 1,2-aryl migration of allylic alcohols was reported with up to 93% yields.

Cu(OAc)2-catalyzed coupling of aromatic C-H bonds with arylboron reagents

Cu-catalyzed coupling of aryl C-H bonds with arylboron reagents was accomplished using a readily removable directing group, which provides a useful method for the synthesis of biaryl compounds. The distinct transmetalation step in this Cu-catalyzed C-H coupling with aryl borons provides unique evidence for the formation of an aryl cupperate intermediate.

Room-temperature Cu(ii)-catalyzed aromatic C–H azidation for the synthesis of ortho-azido anilines with excellent regioselectivity

An efficient synthesis of ortho-aniline derivatives through aromatic C–H azidation catalyzed by Cu(OAc)₂ have been disclosed. The amino group plays an ortho-directing effect in the azidation reactions, regiospecifically affording the mono-azidated derivative as the sole products.

Synthesis of pinacol arylboronates from aromatic amines: a metal-free transformation

A metal-free borylation process based on Sandmeyer-type transformation using arylamines derivatives as the substrates has been developed. Through optimization of the reaction conditions, this novel conversion can be successfully applied to a wide range of aromatic amines, affording borylation products in moderate to good yields. Various functionalized arylboronates, which are difficult to access by other methods, can be easily obtained with this metal-free transformation. Moreover, this transformation can be followed by Suzuki-Miyaura cross-coupling without purification of the borylation products, which enhances the practical usefulness of this method. A possible reaction mechanism involving radical species has been proposed.