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

Pd-catalyzed α-selective C(sp3)–H acetoxylation of amides through an unusual cyclopalladation mechanism

A novel Pd-catalyzed site-selective α-C(sp³)–H oxidation/acetoxylation of amides through an unusual [4,6]-bicyclic metallacycle intermediate was reported with 1-aminoanthraquinone as a new BDG.

Palladium-catalyzed unactivated β-methylene C(sp3)–H bond alkenylation of aliphatic amides and its application in a sequential C(sp3)–H/C(sp2)–H bond alkenylation

A palladium(ii)-catalyzed β-methylene C(sp³)–H bond alkenylation of acyclic aliphatic amides with alkenyl halides has been developed. Solvent effect-promoted sequential C(sp³)–H bond alkenylation and C(sp²)–H bond alkenylation has also been studied.

Multi-site cyclization via initial C–H activation using a rhodium(iii) catalyst: rapid assembly of frameworks containing indoles and indolines

Tandem multi-site cyclization triggered by Rh(iii)-catalyzed C–H activation has been achieved for highly efficient synthesis of spirocycle indolin-3-one (C2-cyclization), benzo[a]carbazole (C3-cyclization) and an unusual indoxyl core (N1-cyclization).

The direct α-C(sp3)–H functionalisation of N-aryl tetrahydroisoquinolines via an iron-catalysed aerobic nitro-Mannich reaction and continuous flow processing

An efficient nitro-Mannich type direct α-C(sp³)–H functionalisation of N-aryl-1,2,3,4-tetrahydroisoquinolines catalysed by simple iron salts in combination with O₂ as the terminal oxidant is described.

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.

A nickel-mediated oxidative α-C(sp3)–H functionalization of amides with allylic alcohols terminated by radical 1,2-aryl migration

A Ni-mediated oxidative C(sp³)–H functionalization of N,N-substituted amides with α,α-diaryl allylic alcohols through a radical 1,2-aryl migration process has been developed. This process features a broad substrate scope and excellent functional group tolerance.

Synthesis of indoles and polycyclic amides via ruthenium(ii)-catalyzed C–H activation and annulation

Ruthenium(ii)-catalyzed oxidative coupling of NH protic amides with alkynes has been developed for the synthesis of a diversity of complex structures, such as N-acyl indole and tricyclic amide derivatives.

Chemoselective activation of sp(3) vs sp(2) C-H bonds with Pd(II)

The first selective coupling of a carbon nucleophile with methyl, ethyl, propyl, and butyl arenes in the absence of a directing group is described. Pd(OAc)₂ double C–H activation displays remarkable selectivity for the terminal methyl sites in alkyl arenes, rather than the more commonly observed arene sp² C–H activation. Mechanistic studies indicate the intermediacy of an azlactone dimer, obtained from oxidation with Pd(OAc)₂, and are consistent with a Pd-catalyzed C–H activation vs a radical process. The observed reactivity establishes that typical reaction solvents (e.g., toluene) can readily participate in C–H activation chemistry.

Nickel-Mediated Synthesis of Isoindolinones at Room Temperature

This communication describes a method for the Ni(cod) 2-mediated intramolecular arylation of alkyl C-H bonds adjacent to the nitrogen atom in benzamide substrates. The transformation proceeds at room temperature and exhibits selectivity for functionalization of more substituted C-H bonds. The yields of the desired isoindolinone products are higher with benzamide substrates containing tertiary alkyl groups on the nitrogen atom than with those bearing primary or secondary alkyls. The results described herein suggest a mechanism involving radical intermediates for these reactions.

Key mechanistic features of Ni-catalyzed C-H/C-O biaryl coupling of azoles and naphthalen-2-yl pivalates

The mechanism of the Ni-dcype-catalyzed C-H/C-O coupling of benzoxazole and naphthalen-2-yl pivalate was studied. Special attention was devoted to the base effect in the C-O oxidative addition and C-H activation steps as well as the C-H substrate effect in the C-H activation step. No base effect in the C(aryl)-O oxidative addition to Ni-dcype was found, but the nature of the base and C-H substrate plays a crucial role in the following C-H activation. In the absence of base, the azole C-H activation initiated by the C-O oxidative addition product Ni(dcype)(Naph)(PivO), 1B, proceeds via ΔG = 34.7 kcal/mol barrier. Addition of Cs2CO3 base to the reaction mixture forms the Ni(dcype)(Naph)[PivOCs·CsCO3], 3_Cs_clus, cluster complex rather than undergoing PivO(-) → CsCO3(-) ligand exchange. Coordination of azole to the resulting 3_Cs_clus complex forms intermediate with a weak Cs-heteroatom(azole) bond, the existence of which increases acidity of the activated C-H bond and reduces C-H activation barrier. This conclusion from computation is consistent with experiments showing that the addition of Cs2CO3 to the reaction mixture of 1B and benzoxazole increases yield of C-H/C-O coupling from 32% to 67% and makes the reaction faster by 3-fold. This emerging mechanistic knowledge was validated by further exploring base and C-H substrate effects via replacing Cs2CO3 with K2CO3 and benzoxazole (1a) with 1H-benzo[d]imidazole (1b) or quinazoline (1c). We proposed the modified catalytic cycle for the Ni(cod)(dcype)-catalyzed C-H/C-O coupling of benzoxazole and naphthalen-2-yl pivalate.

Cobalt-catalyzed, aminoquinoline-directed C(sp²)-H bond alkenylation by alkynes

A method for cobalt-catalyzed, aminoquinoline- and picolinamide-directed C(sp(2))-H bond alkenylation by alkynes was developed. The method shows excellent functional-group tolerance and both internal and terminal alkynes are competent substrates for the coupling. The reaction employs a Co(OAc)2⋅4 H2O catalyst, Mn(OAc)2 co-catalyst, and oxygen (from air) as a terminal oxidant.

Palladium-Catalyzed Direct α-Aryation of Benzyl Thioethers with Aryl Bromides

The arylation of sp3-hybridized C-H's bonds is a powerful strategy to build molecular complexity and diversity. A novel and efficient palladium-catalyzed direct sp3 C-H arylation of aryl and alkyl benzyl thioether derivatives with aryl bromides is reported. The reaction involves reversible deprotonation of the benzylic C-H's of the thioether with either LiN(SiMe3)2 or NaN(SiMe3)2 and subsequent cross-coupling to provide the functionalized products in up to 97% yield. A screen of 24 of the most successful ligands in cross-coupling chemistry led to the identification of NiXantPhos as the only viable ligand for this challenging coupling.

Cu-catalyzed arylcarbocyclization of alkynes with diaryliodonium salts through C-C bond formation on inert C(sp3)-H bond

Copper-catalyzed arylcarbocyclization reaction of alkynes was realized with diaryliodonium salts through C-C bond formation on an inert C(sp3)-H bond. This method provides an efficient cyclization of alkyl alkynes to generate carbocycles with good step-economy. Theoretical study revealed an interesting Cu-catalyzed concerted pathway of the C-C bond formation.

The C-H activation/1,3-diyne strategy: highly selective direct synthesis of diverse bisheterocycles by Rh(III) catalysis

The reactivity and selectivity of 1,3-diynes in transition-metal-catalyzed CH activation is exploited to quickly assemble diverse polysubstituted bisheterocycles, which are highly important but difficult to access. By using the CH activation/1,3-diyne strategy, we overcame the challenges of selectivity (chemo-, regio-, and mono-/diannulation) and constructed seven kinds of adjacent bisheterocycles through the formation of four strategic bonds with high efficiency and high selectivity.