Xukai Zhou

Redox-Neutral Couplings between Amides and Alkynes via Cobalt(III)-Catalyzed C–H Activation

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.

Cobalt(III)-Catalyzed C–C Coupling of Arenes with 7-Oxabenzonorbornadiene and 2-Vinyloxirane via C–H Activation

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.

Access to Structurally Diverse Quinoline-Fused Heterocycles via Rhodium(III)-Catalyzed C–C/C–N Coupling of Bifunctional Substrates

Rhodium(III)-catalyzed C-H activation of heteroarenes and functionalization with bifunctional substrates such as anthranils allows facile construction of quinoline-fused heterocycles under redox-neutral conditions. The couplings feature broad substrate scope and provide step-economical access to two classes of quinoline-fused condensed heterocycles.

Sulfoxonium Ylides as a Carbene Precursor in Rh(III)-Catalyzed C–H Acylmethylation of Arenes

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.

Rhodium(III)-Catalyzed Synthesis of Naphthols via C–H Activation of Sulfoxonium Ylides

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.

Rh(III)-Catalyzed Acceptorless Dehydrogenative Coupling of (Hetero)arenes with 2-Carboxyl Allylic Alcohols

Rhodium(III)-catalyzed C-H activation of (hetero)arenes and redox-neutral coupling with 2-carboxyl allylic alcohols has been realized for the construction of β-aryl ketones. This reaction occurred efficiently at a relatively low catalyst loading via initial dehydrogenative alkylation to give a β-keto carboxylic acid, followed by decarboxylation.

Rhodium(III)-Catalyzed Acylation of C(sp3)–H Bonds with Cyclopropenones

Rh(III)-catalyzed activation and acylation of sp3 C-H bonds has been realized with diarylcyclopropenone as an acylating reagent. Both benzylic C-H in 8-methylquinolines and unactivated C-H in 2-alkylpyridines are applicable in this C-H acylation reaction, providing enones in good yields under redox-neutral conditions.

Access to Substituted Propenoic Acids via Rh(III)-Catalyzed C–H Allylation of (Hetero)Arenes with Methyleneoxetanones

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.

Divergent Coupling of Anilines and Enones by Integration of C−H Activation and Transfer Hydrogenation

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.