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Rh(III)-catalyzed, chelation-assisted oxidative C−H imidation of arenes with N−H imide have been realized using PhI(OAc)2 as an oxidant. This transformation exhibits a broad substrate scope and tolerates various functional groups. The reaction proceeded via in situ generation of an iodine(III) imido. DFT calculations suggest that this oxidative imidaton system proceeds via a Rh(III)-Rh(V)-Rh(III) pathway.

Rh(III)-catalyzed C–H activation of N-protected anilines and chemo-divergent couplings with acroleins/enones have been realized for synthesis of three classes of heterocycles. The oxidative coupling of N-pyridylaniline afforded dihydroquinolones with the acrolein being a major hydrogen acceptor. When the directing group was replaced by pyrimidyl in the same system, redox-neutral coupling occurred to afford hemiaminal ethers. Oxidative annulation of N-pyridylanilines with enones using AgBF4 oxidant afforded atropisomeric quinolinium salts.

Manganese(I)-catalyzed C–H activation of indoles and divergent annulative coupling with alkyne-tethered cyclohexadienones has been realized under operationally simple conditions. These annulation systems are under condition control. The coupling in the presence of BPh3 additive followed a C–H activation-alkyne insertion-Michael addition pathway, affording an exocyclic olefin attached to a tetrahydrofuran ring. In contrast, when Zn(OAc)2/PivOH additives were introduced, initial olefination en route to intramolecular Diels–Alder reaction and subsequent elimination of an alcohol was followed to deliver a fused six-membered ring. The selectivity stands in contrast to those reported using rhodium(III) and cobalt(III) catalysts, highlighting the unique reactivity and selectivity of manganese catalysts.

Cp*RhIII /IrIII complexes are known to play important roles in both C-H activation and transfer hydrogenation (TH). However, these two areas evolved separately. They have been integrated in redox- and chemodivergent coupling reactions of N-pyridylanilines with enones. The iridium-catalyzed coupling with enones leads to the efficient synthesis of tetrahydroquinolines through TH from i PrOH. Counterintuitively, i PrOH does not serve as the sole hydride source, and the major reaction pathway involves disproportionation of a dihydroquinoline intermediate, followed by the convergent and iterative reduction of quinolinium species.

An efficient, atom-economical, and regioselective insertion of indoles into terminal alkynes has been realized via cobalt(III)-catalyzed C–H activation under mild conditions, leading to efficient synthesis of α-gem-vinylindoles. The insertion of the alkynes follows a rare 1,2-selectivity, and silyl alkynes, alkyl alkynes, propargyl alcohols, and protected propargyl amines are all applicable. The mechanism of this hydroarylation system has been studied in detail by a combination of experimental and computational approaches. In the reaction of silyl terminal alkynes, the regioselectivity is dictated by the steric effects of the alkyne substituent, especially in the protonolysis stage. However, for protected propargyl amines, the selectivity results from electronic effects during the insertion step, with protonolysis being insignificant in the determination of selectivity. An internal alkyne also coupled in high efficiency but with low regioselectivity. Comparisons of cobalt, rhodium, and iridium catalysts h...

Sulfoxonium ylides act as an efficient carbene precursor in rhodium(III)-catalyzed C-H acylmethlyation of a variety of arenes assisted by different chelating groups, and both aryl- and alkyl-substituted β-carbonyl sulfoxonium ylides are applicable. The system proceeded under redox-neutral conditions with a broad scope, high efficiency, and functional group tolerance.

Carbonyl groups are ubiquitous in functional molecules. Although C–H bond acylation has been well-studied via different mechanisms, transition-metal-catalyzed redox-neutral C(sp3)–H acylation under mild conditions is unprecedented. In this work, ketene is designed as a acylating reagent for both C(sp3)–H and C(sp2)–H bonds under Rh(III) catalysis, affording a diverse array of carbonyl compounds in high yields and high atom economy under mild conditions.

Co(III)-catalyzed mild C-C couplings of arenes with strained rings such as 7-oxabenzonorbornadienes and 2-vinyloxirane have been realized. The transformation is proposed to undergo ortho C-H activation, olefin insertion, and subsequent β-oxygen elimination. A broad range of synthetically useful functional groups are compatible, thus providing a new entry to access diversely 2-functionalized indoles.

Previous direct C-H nitrogenation suffered from simple amidation/amination with limited atom-economy and is mostly limited to C(sp(2) )-H substrates. In this work, anthranil was designed as a novel bifunctional aminating reagent for both C(sp(2) )-H and C(sp(3) )-H bonds under rhodium(III) catalysis, thus affording a nucleophilic aniline tethered to an electrophilic carbonyl. A tridendate rhodium(III) complex has been isolated as the resting state of the catalyst, and DFT studies established the intermediacy of a nitrene species.

C-H activation assisted by a bifunctional directing group has allowed the construction of heterocycles. This is ideally catalyzed by earth-abundant and eco-friendly transition metals. We report Co(III)-catalyzed redox-neutral coupling between arenes and alkynes using an NH amide as an electrophilic directing group. The redox-neutral C-H activation/coupling afforded quinolines with water as the sole byproduct.

Rhodium-catalyzed C–H activation of arenes has been established as an important strategy for the rapid construction of new bonds. On the other hand, ring-opening of readily available cyclopropanols has served as a driving force for the coupling with various nucleophiles and electrophiles. Nevertheless, these two important areas evolved separately, and coupling of arenes with cyclopropanols via C–H activation has been rarely explored. In this work, the oxidative coupling between arenes and cyclopropanols has been realized with high efficiency and selectivity under Rh(III)-catalysis, providing an efficient route to access β-aryl ketones. Moreover, the C–H bond has been extended to benzylic C–H bonds.

An efficient synthesis of disubstituted acrylic acids has been realized via Rh(III)-catalyzed C–H activation of (hetero)arenes and coupling with four-membered methyleneoxetanones under redox-neutral conditions. In most cases, the reactions are silver-free, and the products are exclusively E-selective with a broad substrate scope. The transformation proceeds via ortho C–H activation followed by selective olefin insertion and β-oxygen elimination.

Rhodium(III)-catalyzed mild benzylic α-fluoroalkenylation of 8-methylquinolines with gem-difluorostyrenes has been developed. This reaction occurred via C–H activation and C–F cleavage and is applicable to a wide range of substrates, leading to the synthesis of Z-alkenyl fluorides under mild and redox-neutral conditions with high regio- and stereoselectivity.

Direct and efficient synthesis of 1-naphthols has been realized via Rh(III)-catalyzed C–H activation of sulfoxonium ylides and subsequent annulation with alkynes, where the sulfoxonium ylide functioned as a new traceless bifunctional directing group. This reaction occurred under redox-neutral conditions with a broad substrate scope.

Rhodium(III)- and cobalt(III)-catalyzed C-H activation of indoles and coupling with 1,6-enynes is discussed. Under rhodium(III) catalysis, the alkyne insertion follows 2,1-regioselectivity with a subsequent type-I intramolecular Diels-Alder reaction (IMDA) to afford [6,5]-fused cycles. When catalyzed by the cobalt(III) congener, 1,2-insertion of the alkyne is preferred, and followed by a rare type-II IMDA, thus leading to bridged [3,3,1]-cycles. This selectivity of the alkyne insertion was mainly tuned by the steric sensitivity of the catalyst.

A cobalt(III)-catalyzed α-fluoroalkenylation of different arenes with readily available gem-difluorostyrenes has been realized under mild and redox-neutral conditions. This reaction occurs via a C–H activation pathway and offers a step-economical access to various 1,2-diaryl-substituted monofluoroalkenes in excellent Z selectivity in moderate to excellent yields.

Quinazoline N-oxides have been prepared from simple ketoximes and 1,4,2-dioxazol-5-ones via Rh(III)-catalyzed C–H activation–amidation of the ketoximes and subsequent Zn(II)-catalyzed cyclization. The substrate scope and functional group compatibility were examined. The reaction features relay catalysis by Rh(III) and Zn(II).

Co(III)-catalyzed mild C–C couplings of arenes with strained rings such as 7-oxabenzonorbornadienes and 2-vinyloxirane have been realized. The transformation is proposed to undergo ortho C–H activation, olefin insertion, and subsequent β-oxygen elimination. A broad range of synthetically useful functional groups are compatible, thus providing a new entry to access diversely 2-functionalized indoles.

The rhodium(III)-catalyzed regioselective alkylation of (hetero)arenes using cyclopropanols as a reactive and efficient coupling partner under oxidative conditions has been developed. This coupling occurred at room temperature via C–H activation of arenes and C–C cleavage of cyclopropanols. Various types of (hetero)arenes (indolines, carbazole, tetrahydrocarbazole, pyrrole, thiophene, etc.) were all successfully reacted under the present conditions. This protocol provides the facile and efficient construction of C7-alkylated indoline scaffolds.

Mild and efficient synthesis of benzophenones via Ir(iii)- and Rh(iii)-catalyzed, directing group-assisted formyl C–H arylation of benzaldehydes has been achieved using diaryliodonium salts, in which Rh(iii) and Ir(iii) catalysts exhibited a complementary substrate scope.

The rhodium(III)-catalyzed regioselective alkylation of (hetero)arenes using cyclopropanols as a reactive and efficient coupling partner under oxidative conditions has been developed. This coupling occurred at room temperature via C–H activation of arenes and C–C cleavage of cyclopropanols. Various types of (hetero)arenes (indolines, carbazole, tetrahydrocarbazole, pyrrole, thiophene, etc.) were all successfully reacted under the present conditions. This protocol provides the facile and efficient construction of C7-alkylated indoline scaffolds.