Cobalt(II)-Catalyzed Oxidative C–H Arylation of Indoles and Boronic Acids

Pyrimidine as an Aryl C-H Activating Group

The Pd-catalyzed regioselective C-H activation/arylation, /iodination, and/acetoxylation reactions of 4-arylpyrimidines using aryl iodides, N-iodosuccinimide, and (diacetoxyiodo)benzene respectively as coupling partners are described. Suzuki-Miyaura coupling and Sonogashira reactions of the resulting aryl iodides are demonstrated. The scalability of the C-H activation/functionalization starting with readily accessible 4-aryl pyrimidines is also reported.

Cobalt-Carbon Bond Formation Reaction via Ligand Reduction of Porphycene-Cobalt(II) Complex and Its Noninnocent Reactivity

The interesting redox properties and reactivity of metalloporphycene have been studied for decades; however, the detailed experimental investigation on the reactivity and reaction mechanism under inert condition combined with theoretical calculations had not been performed so far. In this study, the novel reactivity of the reduced form of the cobalt porphycene with alkyl halides to form cobalt-carbon (Co-C) bonds was revealed. Under electrochemical reductive conditions, not the central cobalt, but the ligand was reduced and reacted with alkyl halides to afford the cobalt-alkyl complexes under N₂ atmosphere in a glovebox. The reaction mechanism was clarified by the combination of experimental and theoretical studies that the porphycene ligand works as a noninnocent ligand and allows the S_N2-type Co-C bond formation. This result provides us the possibility of the reaction triggered by the reduction of ligand with macrocyclic π-conjugated system, not by the reduction of metal.

Copper-mediated regioselective C-H etherification of naphthylamides with arylboronic acids using water as an oxygen source

The copper-mediated regioselective C-H activation and C-O bond formation of naphthylamides with arylboronic acids has been developed using water as an oxygen source. The kinetic isotope study suggests that C-H bond activation is the rate-determining step. The H2O18 labelling experiment reveals the incorporation of oxygen from water. The substrate scope, functional group diversity and post synthetic utilities are the important practical features.

Expedient cobalt(ii)-catalyzed site-selective C7-arylation of indolines with arylboronic acids

Cobalt(ii)-catalyzed pyrimidyl directing group-assisted C7 arylation of indolines with arylboronic acids has been developed using Mn(OAc)₂·4H₂O as an oxidant. The use of cobalt(ii)-PCy₃ as a catalyst and broad substrate scope are the important practical features.

Cobalt-catalyzed carbon–sulfur/selenium bond formation: synthesis of benzo[b]thio/selenophene-fused imidazo[1,2-a]pyridines

An efficient cobalt-catalyzed C–S/C–Se bond formation method for the synthesis of benzo[b]thio/selenophene-fused imidazo[1,2-a]pyridines has been developed.

Weak, bidentate chelating group assisted cross-coupling of C(sp3)–H bonds in aliphatic acid derivatives with aryltrifluoroborates

A novel weak, bidentate directing group enabled β-C(sp³)–H cross-coupling of aliphatic acids that contain α-hydrogen atoms with organoboron reagents.

A 2-(1-methylhydrazinyl)pyridine-directed C–H functionalization/spirocyclization cascade: facile access to spirosuccinimide derivatives

A cobalt-catalyzed oxidative coupling of benzoic hydrazides with maleimides by utilizing 2-(1-methylhydrazinyl)pyridine as a bidentate directing group has been developed.

Suzuki–Miyaura coupling of unstrained ketones via chelation-assisted C–C bond cleavage

Herein, we report that unstrained ketones can be efficiently employed as electrophiles in Suzuki–Miyaura reactions via catalytic activation of unstrained C–C bonds assist by an N-containing directing group.

Iron(ii)-catalyzed C-2 cyanomethylation of indoles and pyrroles via direct oxidative cross-dehydrogenative coupling with acetonitrile derivatives

A novel and efficient approach for the C(sp²)–H/C(sp³)–H oxidative coupling of indoles and pyrroles with acetonitrile derivatives was reported by using the Fe(ii) complex.

Cobalt-catalyzed C–H activation: recent progress in heterocyclic chemistry

Cobalt-catalyzed C–H activation has gone through some major advancements in the past couple of decades.

Electrochemical Cobalt-Catalyzed C-H Oxygenation at Room Temperature

Electrochemical cobalt-catalyzed C-H functionalizations were achieved in terms of C-H oxygenation under mild conditions at 23 °C. The robust electrochemical C-H functionalization was characterized by ample substrate scope, whereas mechanistic studies provided support for a facile C-H cleavage. The electrochemical cobalt-catalyzed C-H oxygenation proved viable on arenes and alkenes with excellent levels of positional and diastereo-selectivity, avoiding the use of stoichiometric silver(I) oxidants under ambient conditions.

Pd-catalyzed regioselective intramolecular direct arylation of 3-indolecarboxamides: access to spiro-indoline-3,3′-oxindoles and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones

We report regioselective intramolecular direct C-3 and C-2 arylations of the indole rings of 3-indolecarboxamides for diastereospecific production of spiro-indoline-3,3′-oxindoles and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones, respectively, under different reaction conditions.

Transition metal-catalyzed site- and regio-divergent C–H bond functionalization

The regioselectivity of C–H functionalization reactions can be redirected to obtain regioisomeric products form the same starting materials.