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

Aryl Bromides and Aryl Chlorides for the Direct Arylation of Benzylic Amines Mediated by Ruthenium(II)

The ruthenium(II)-catalyzed sp3 C-H bond arylation of benzylic amines with aryl halides is reported. In the present method, aryl iodides and, more importantly, also the cheaper aryl bromides and aryl chlorides can be applied as aryl sources. Additionally, the method does not require elaborate manipulations in a glove box and can be carried out in simple screw cap vials. Potassium pivalate proved to be beneficial for the transformation with aryl bromides or iodides as aryl source, but was not required for aryl chlorides. In the latter case, the addition of PPh3 led to high conversion. 3-Methyl and 3-phenyl pyridine were established as directing groups, and the substituent in the 3-position represents a key structural feature for high conversion. The directing group can be cleaved after the transformation, which allows access to diarylmethylamines. Mechanistic studies were carried out and critically compared to mechanistic reports of related transformations.

A highly tunable stereoselective dimerization of methyl ketone: efficient synthesis of E- and Z-1,4-enediones

A new method for the tunable synthesis of 1,4-enedione directly from aromatic methyl ketone is described. This tandem reaction enables the construction of symmetric and unsymmetric 1,4-enediones with complete E-selectivity. Moreover, the resulting E-1,4-enedione could be transformed into a Z-isomer by irradiation with 23 W of white light.

β-Arylation of carboxamides via iron-catalyzed C(sp3)-H bond activation

A 2,2-disubstituted propionamide bearing an 8-aminoquinolinyl group as the amide moiety can be arylated at the β-methyl position with an organozinc reagent in the presence of an organic oxidant, a catalytic amount of an iron salt, and a biphosphine ligand at 50 °C. Various features of selectivity and reactivity suggest the formation of an organometallic intermediate via rate-determining C-H bond cleavage rather than a free-radical-type reaction pathway.

C(sp3)-H bond arylations catalyzed by well-defined [Ru(O2CMes)2(p-cymene)]

The well-characterized ruthenium(II) biscarboxylate complex [Ru(O2CMes)2(p-cymene)] enabled versatile direct (hetero)arylations of C(sp(3))-H bonds with low (co)catalyst loading and ample substrate scope. Detailed mechanistic studies provided strong support for a facile and reversible C(sp(3))-H bond metalation.

First selective direct mono-arylation of piperidines using ruthenium-catalyzed C-H activation

Abstract

A Ru-catalyzed mono-arylation in α-position of saturated cyclic amines is reported employing a C–H activation protocol. Substitution of the pyridine directing group with a bulky group, e.g., trifluoromethyl in the 3-position, proved to be crucial to avoid bis-arylation. This highly selective transformation can be performed with different amines and arylboronate esters. Additionally, the directing group can be cleaved, taking advantage of an unprecedented detrifluoromethylation reaction.

Graphical Abstract

Synthesis of functionalized spiroindolines via palladium-catalyzed methine C-H arylation

The synthesis of cyclopropyl spiroindolines is described using an intramolecular palladium(0)-catalyzed C-H functionalization of a methine C(sp(3))-H bond. This transformation can be coupled with intermolecular Suzuki couplings or direct arylations of heteroaromatics to access functionalized indoline scaffolds in a single step.

Iron-catalyzed allylic arylation of olefins via C(sp3)-H activation under mild conditions

An aryl Grignard reagent in the presence of mesityl iodide converts an allylic C-H bond of a cycloalkene or an allylbenzene derivative into a C-C bond in the presence of a catalytic amount of Fe(acac)(3) and a diphosphine ligand at 0 °C. The stereo- and regioselectivity of the reaction, together with deuterium labeling experiments, suggest that C-H bond activation is the slow step in the catalytic cycle preceding the formation of an allyliron intermediate.

Mechanistic investigations and substrate scope evaluation of ruthenium-catalyzed direct sp3 arylation of benzylic positions directed by 3-substituted pyridines

A highly efficient direct arylation process of benzylic amines with arylboronates was developed that employs Ru catalysis. The arylation takes place with greatest efficiency at the benzylic sp(3) carbon. If the distance to the activating aryl ring is increased, arylation is still possible but the yield drops significantly. Efficiency of the CH activation was found to be significantly increased by use of 3-substituted pyridines as directing groups, which can be removed after the transformation in high yield. Calculation of the energy profile of different rotamers of the substrate revealed that presence of a substituent in the 3-position favors a conformation with the CH(2) group adopting a position in closer proximity to the directing group and facilitating C-H insertion. This operationally simple reaction can be carried out in argon atmosphere as well as in air and under neutral reaction conditions, displaying a remarkable functional group tolerance. Mechanistic studies were carried out and critically compared to mechanistic reports of related transformations.

Silver-catalyzed oxidative coupling/cyclization of acrylamides with 1,3-dicarbonyl compounds

An efficient silver-catalyzed oxidative cyclization of acrylamides with 1,3-dicarbonyl compounds is described. It proceeds through a tandem radical addition/cyclization process, in which two new C–C bonds were formed.

Ligand-enabled methylene C(sp3)-H bond activation with a Pd(II) catalyst

Pd(II) insertion into β-methylene C(sp(3))-H bonds was enabled by a mutually repulsive and electron-rich quinoline ligand. Ligand tuning led to the development of a method that allows for installation of an aryl group on a range of acyclic and cyclic amides containing β-methylene C(sp(3))-H bonds.