Singlet-Oxygen-Driven Cooperative Photocatalytic Coupling of Biomass Valorization and Hydrogen Peroxide Production Using Covalent Organic Frameworks.

Traditional HO photocatalysis primarily depends on photoexcited electrons and holes to drive oxygen reduction and water oxidation, respectively. However, singlet oxygen (O), often underappreciated, plays a pivotal role in HO production. Meanwhile, photocatalytic biomass conversion has attracted attention, yet studies combining HO synthesis with biomass valorization remain rare and typically yield low-value products.

Methyl Ketones as Alkyl Halide Surrogates: A Deacylative Halogenation Approach for Strategic Functional Group Conversions.

Alkyl halides are versatile precursors to access diverse functional groups (FGs). Due to their lability, the development of surrogates for alkyl halides is strategically important for complex molecule synthesis. Given the stability and ease of derivatization inherent in common alkyl ketones, here we report a deacylative halogenation approach to convert various methyl ketones to the corresponding alkyl chlorides, bromides, and iodides.

Deacylative Thiolation by Redox-Neutral Aromatization-Driven C-C Fragmentation of Ketones.

Herein we report the development of deacylative thiolation of diverse methyl ketones. The reaction is redox-neutral, and heavy-metal-free, which provides a new way to introduce thioether groups site-specifically to unactivated aliphatic positions. It also features excellent functional group tolerance and broad substrate scope, thus allowing late-stage derivatization.

Site-Specific and Degree-Controlled Alkyl Deuteration via Cu-Catalyzed Redox-Neutral Deacylation.

Deuterated organic compounds have become increasingly important in many areas; however, it remains challenging to install deuterium site-selectively to unactivated aliphatic positions with control of the degree of deuteration. Here, we report a Cu-catalyzed degree-controlled deacylative deuteration of diverse alkyl groups with the methylketone (acetyl) moiety as a traceless activating group. The use of -methylpicolino-hydrazonamide (MPHA) promotes efficient aromatization-driven C-C cleavage.

Deacylation-Aided C─H Alkylative Annulation through C─C Cleavage of Unstrained Ketones.

Arene- and heteroarene-fused rings are pervasive in biologically active molecules. Direct annulation between a C─H bond on the aromatic core and a tethered alkyl moiety provides a straightforward approach to access these scaffolds; however, such a strategy is often hampered by the need of special reactive groups and/or less compatible cyclization conditions. It would be synthetically appealing if a common native functional group can be used as a handle to enable a general C─H annulation with diverse aromatic rings.

Olefination via Cu-Mediated Dehydroacylation of Unstrained Ketones.

The dehydroacylation of ketones to olefins is realized under mild conditions, which exhibits a unique reaction pathway involving aromatization-driven C-C cleavage to remove the acyl moiety, followed by Cu-mediated oxidative elimination to form an alkene between the α and β carbons. The newly adopted '-methylpicolinohydrazonamide (MPHA) reagent is key to enable efficient cleavage of ketone C-C bonds at room temperature. Diverse alkyl- and aryl-substituted olefins, dienes, and special alkenes are generated with broad functional group tolerance.

Rhodium-Catalyzed Atroposelective Access to Axially Chiral Olefins via C-H Bond Activation and Directing Group Migration.

Axially chiral open-chain olefins represent an underexplored class of chiral platform. In this report, two classes of tetrasubstituted axially chiral acyclic olefins have been accessed in excellent enantioselectivity and regioselectivity via C-H activation of (hetero)arenes assisted by a migratable directing group en route to coupling with sterically hindered alkynes. The coupling of indoles bearing an N-aminocarbonyl directing group afforded C-N axially chiral acrylamides with the assistance of a racemic zinc carboxylate additive.

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

Cp*Rh /Ir 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.

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.

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.

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 regio- and stereoselective benzylic α-fluoroalkenylation with gem-difluorostyrenes.

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.

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.

Rhodium(III)-Catalyzed Acylation of C(sp)-H Bonds with Cyclopropenones.

Rh(III)-catalyzed activation and acylation of sp 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.

Catalyst-Controlled Regiodivergent Alkyne Insertion in the Context of C-H Activation and Diels-Alder Reactions: Synthesis of Fused and Bridged Cycles.

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.

Cp*Rh(III)-Catalyzed Mild Addition of C(sp)-H Bonds to α,β-Unsaturated Aldehydes and Ketones.

A Rh(III)-catalyzed addition of benzylic C(sp)-H bond to α,β-unsaturated ketones/aldehydes has been realized, leading to efficient synthesis of γ-aryl ketones/aldehydes. This atom-economic reaction proceeded under mild and redox-neutral conditions with a broad substrate scope. Besides benzylic C-H, allylic C-H bonds are also applicable when assisted by O-methyl ketoxime directing groups.

Cobalt(III)-Catalyzed Regio- and Stereoselective α-Fluoroalkenylation of Arenes with gem-Difluorostyrenes.

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.

Rh(III)- and Zn(II)-Catalyzed Synthesis of Quinazoline N-Oxides via C-H Amidation-Cyclization of Oximes.

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).

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.

Iridium- and rhodium-catalyzed C-H activation and formyl arylation of benzaldehydes under chelation-assistance.

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.

Rhodium(III)-Catalyzed Mild Alkylation of (Hetero)Arenes with Cyclopropanols via C-H Activation and Ring Opening.

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.

Anthranil: An Aminating Reagent Leading to Bifunctionality for Both C(sp(3) )-H and C(sp(2) )-H under Rhodium(III) Catalysis.

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.

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.