Rhodium-catalyzed sulfonylation, thioetherification, thiocyanation, and other heterofunctionalizations of arenes bearing a heterocyclic directing group have been realized. The reaction proceeds by initial Rh^III-catalyzed CH hyperiodination of arene at room temperature followed by uncatalyzed nucleophilic functionalization. A diaryliodonium salt is isolated as an intermediate, which represents umpolung of the arene substrate, in contrast to previous studies that suggested umpolung of the coupling partner.

Diaryliodonium salts play an increasingly important role as an aryl source. Reported is the first synthesis of diaryliodoniums by rhodium(III)-catalyzed CH hyperiodination of electron-poor arenes under chelation assistance. This CI coupling reaction occurred at room temperature with high regio-selectivity and functional-group compatibility. Subsequent diversified nucleophilic functionalization of a diaryliodonium allowed facile construction of CC, CN, CO, CS, CP and CBr bonds, and in all cases the initial functionalization occurred at the arene containing the chelating-group.

Metal-catalyzed CH activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N-oxide is used as an arene source in CH activation studies, the NO bond can act as a directing group as well as an O-atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline NO bond and alkynes, which results in CH activation and O-atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a RhC bond, a reductive elimination to form an oxazinoquinolinium-coordinated Rh^I intermediate, an oxidative addition to break the NO bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop-1-yn-1-ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1-phenyl-2-quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity-determining step. These calculated data are consistent with the experimental observations.

Diaryliodonium salts play an increasingly important role as an aryl source. Reported is the first synthesis of diaryliodoniums by rhodium(III)-catalyzed CH hyperiodination of electron-poor arenes under chelation assistance. This CI coupling reaction occurred at room temperature with high regio-selectivity and functional-group compatibility. Subsequent diversified nucleophilic functionalization of a diaryliodonium allowed facile construction of CC, CN, CO, CS, CP and CBr bonds, and in all cases the initial functionalization occurred at the arene containing the chelating-group.

Nitrogenation by direct functionalization of CH bonds represents an important strategy for constructing CN bonds. Rhodium(III)-catalyzed direct amidation of unactivated C(sp³)H bonds is rare, especially under mild reaction conditions. Herein, a broad scope of C(sp³)H bonds are amidated under rhodium catalysis in high efficiency using 3-substituted 1,4,2-dioxazol-5-ones as the amide source. The protocol broadens the scope of rhodium(III)-catalyzed C(sp³)H activation chemistry, and is applicable to the late-stage functionalization of natural products.

Nitrogenation by direct functionalization of CH bonds represents an important strategy for constructing CN bonds. Rhodium(III)-catalyzed direct amidation of unactivated C(sp³)H bonds is rare, especially under mild reaction conditions. Herein, a broad scope of C(sp³)H bonds are amidated under rhodium catalysis in high efficiency using 3-substituted 1,4,2-dioxazol-5-ones as the amide source. The protocol broadens the scope of rhodium(III)-catalyzed C(sp³)H activation chemistry, and is applicable to the late-stage functionalization of natural products.

Metal-catalyzed hydroacylation of olefins represents an important atom-economic synthetic process in CH activation. For the first time highly efficient Rh^IIICp*-catalyzed hydroacylation was realized in the coupling of N-sulfonyl 2-aminobenzaldehydes with both conjugated and aliphatic olefins, leading to the synthesis of various aryl ketones. Occasionally, oxidative coupling occurred when a silver(I) oxidant was used.

[Cp*Rh^III]-catalyzed CH activation of arenes assisted by an oxidizing NO or NN directing group has allowed the construction of a number of hetercycles. In contrast, a polar NO bond is well-known to undergo O-atom transfer (OAT) to alkynes. Despite the liability of NO bonds in both CH activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh^III] catalysts integrate both areas in an efficient redox-neutral coupling of quinoline N-oxides with alkynes to afford α-(8-quinolyl)acetophenones. In this process the NO bond acts as both a directing group for CH activation and as an O-atom donor.

[Cp*Rh^III]-catalyzed CH activation of arenes assisted by an oxidizing NO or NN directing group has allowed the construction of a number of hetercycles. In contrast, a polar NO bond is well-known to undergo O-atom transfer (OAT) to alkynes. Despite the liability of NO bonds in both CH activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh^III] catalysts integrate both areas in an efficient redox-neutral coupling of quinoline N-oxides with alkynes to afford α-(8-quinolyl)acetophenones. In this process the NO bond acts as both a directing group for CH activation and as an O-atom donor.

The rhodium(III)-catalyzed coupling of azomethine ylides with alkynes via CH activation has been developed for the synthesis of indenamines in moderate to high yields. The coupled products can be further oxidized to indenones and derivatives.

Isoquinolines have been synthesized from the redox-neutral dehydrative CN and CC cross-coupling between oximines and alkynes using a catalytic amount of (pentamethylcyclopentadiene)rhodium dichloride dimer {[RhCp*Cl₂]₂} and cesium acetate (CsOAc), a process that involves ortho CH activation of oximines and subsequent functionalization with alkynes. This redox-neutral catalytic isoquinoline synthesis operates under mild conditions, and is insensitive to moisture or air. A broad scope of coupling partners has been established, and a likely mechanism has been suggested.

An overview of reactive gold α-oxo carbenoid intermediates in the gold-catalyzed functionalization of alkynes is presented. Such intermediates can be generated from inter- and intramolecular oxidation of alkynes by nucleophilic oxygen-atom donor groups, such as amine N-oxides, pyridine N-oxides, nitrones, nitro compounds, sulfoxides, and epoxides. These O-atom transfer processes occur by gold-mediated addition–elimination reactions. In catalytic systems, α-oxo carbenoids can undergo nucleophilic attack by imine, arene, and migrating hydride as well as alkyl groups, leading to cascade reactions and the construction of new skeletons. The facile construction of CE (E=C, N, S, or O) bonds makes it an attractive step-economic approach to value-added molecules from readily available starting materials. The scope, mechanisms, and reactivity of such α-oxo carbenoid species are discussed. The remarkable diversity of structures accessible is demonstrated with various recent examples.

Reaktive Gold-α-Oxocarbenoide können als Zwischenstufen in der goldkatalysierten Funktionalisierung von Alkinen auftreten. Derartige Zwischenstufen lassen sich anhand einer inter- und intramolekularen Oxidation von Alkinen mit nukleophilen, Sauerstoff übertragenden Gruppen wie Amin-N-oxiden, Pyridin-N-oxiden, N-Oxiden einer Schiffschen Base (Nitronen), Nitroverbindungen, Sulfoxiden und Epoxiden synthetisieren. Diese Sauerstoffübertragungsprozesse erfolgen als goldvermittelte Additions-Eliminierungs-Reaktionen. In katalytischen Prozessen werden α-Oxocarbenoide von Iminen und Arenen sowie von wandernden Hydriden und Alkylgruppen angegriffen. Diese Reaktionssequenzen führen zu Produkten mit neuen Molekülstrukturen. Der einfache Aufbau von C-E-Einfachbindungen (E=C, N, S oder O) ist ein direkter Weg zu wertvollen Verbindungen aus leicht zugänglichen Ausgangsmaterialien.

A novel nitrone-based pincer ligand was developed by a single-step synthesis from N-(tert-butyl)hydroxylamine acetate and 2,6-pyridinedicarboxaldehyde. The developed ligand allowed us to synthesize a cationic ruthenium pincer complex. A distorted octahedral coordination environment around the ruthenium center was observed. The complex showed excellent catalytic activity in transfer hydrogenation reactions with turnover numbers up to 590,000.