Cascade Oxidative Coupling/Cyclization: A Gateway to 3‑Amino Polysubstituted Five-Membered Heterocycles

Taking advantage of the coordinating activation strategy, we have developed the cascade oxidative coupling/cyclization of α-C­(sp³)–H bonds of amines with enamines or β-keto esters for the synthesis of three types of five-membered heterocycles. α-Amino acids as the substrate lead to 3-amino 1,3-dihydro-2<i>H</i>-pyrrol-2-ones and furan-2­(3<i>H</i>)-ones by using air or dioxygen as the sole clean oxidant, respectively. α-Amino ketones give a range of 3-amino 1<i>H</i>-pyrroles by using di-<i>tert</i>-butyl peroxide as the oxidant. A three-component, one-pot reaction from readily available amine, β-keto ester, and α-amino ketone enhances the practicality of the modular construction of 1<i>H</i>-pyrrole scaffolds. This programmed protocol features simple reaction conditions, readily available starting materials, broad substrate scope, and high functional group tolerance

Rhodium(III)-Catalyzed Oxidative Cross-Coupling of Unreactive C(sp³)–H Bonds with C(sp²)–H Bonds

The development of the oxidative cross-coupling of unreactive C­(sp³)–H bonds with (hetero)­arene C­(sp²)–H bonds is considerably appealing, yet conceptually and practically challenging. Here, we disclose the rhodium-catalyzed oxidative heteroarylation of unactivated C­(sp³)–H bonds with heteroarene C­(sp²)–H bonds. This method provides a step-economic route to β-heteroarylated 2-ethylpyridine derivatives, which exhibits relatively broad substrate scope, high tolerance level of sensitive functional groups, and high selectivity. The protocol can also be extended to the coupling reaction between 8-methylquinoline derivatives and heteroarenes

Cascade Oxidative Coupling/Cyclization: A Gateway to 3‑Amino Polysubstituted Five-Membered Heterocycles

Taking advantage of the coordinating activation strategy, we have developed the cascade oxidative coupling/cyclization of α-C­(sp³)–H bonds of amines with enamines or β-keto esters for the synthesis of three types of five-membered heterocycles. α-Amino acids as the substrate lead to 3-amino 1,3-dihydro-2<i>H</i>-pyrrol-2-ones and furan-2­(3<i>H</i>)-ones by using air or dioxygen as the sole clean oxidant, respectively. α-Amino ketones give a range of 3-amino 1<i>H</i>-pyrroles by using di-<i>tert</i>-butyl peroxide as the oxidant. A three-component, one-pot reaction from readily available amine, β-keto ester, and α-amino ketone enhances the practicality of the modular construction of 1<i>H</i>-pyrrole scaffolds. This programmed protocol features simple reaction conditions, readily available starting materials, broad substrate scope, and high functional group tolerance

RhCl₃‑Catalyzed Oxidative C–H/C–H Cross-Coupling of (Hetero)aromatic Sulfonamides with (Hetero)arenes

1,1′-Bi­(hetero)­aryl 2-sulfonamide scaffolds have been widely used as a privileged structure in drug discovery. Herein, we report an efficient rhodium-catalyzed oxidative C–H/C–H cross-coupling between a (hetero)­aromatic sulfonamide and a (hetero)­arene to afford <i>ortho</i>-sulfonamido bi­(hetero)­aryls. This methodology features broad substrate scope, good functional group tolerance, and relatively inexpensive catalyst (without the use of RhCp*). A wide range of (hetero)­arenes such as thiophenes, benzothiophenes, pyrroles, furans, benzofuran, indolizine, and simple arenes can engage in this transformation. This protocol also provides a facile route to bi­(hetero)­aryl sultams and dibenzo­[<i>b</i>,<i>d</i>]­thiophene 5,5-dioxides through further intramolecular cyclization, indicating its potential application in materials exploitation

Copper-Mediated Tandem Oxidative C(sp²)–H/C(sp)–H Alkynylation and Annulation of Arenes with Terminal Alkynes

The copper-mediated tandem oxidative C­(sp²)–H/C­(sp)–H cross-coupling and intramolecular annulation of arenes with terminal alkynes has been developed, which offers a highly efficient approach to the 3-methyleneisoindolin-1-one scaffold. In this oxidative coupling process, Cu­(OAc)₂ acts as both the promoter and the terminal oxidant. This protocol features a wide substrate scope; high functional group tolerance; exclusive chemo-, regio-, and stereoselectivity; and simple, easily available, and inexpensive reaction system. The transformation has demonstrated for the first time that Cu­(OAc)₂ can be renewable after undergoing an oxidative reaction

Copper-Mediated Tandem Oxidative C(sp²)–H/C(sp)–H Alkynylation and Annulation of Arenes with Terminal Alkynes

The copper-mediated tandem oxidative C­(sp²)–H/C­(sp)–H cross-coupling and intramolecular annulation of arenes with terminal alkynes has been developed, which offers a highly efficient approach to the 3-methyleneisoindolin-1-one scaffold. In this oxidative coupling process, Cu­(OAc)₂ acts as both the promoter and the terminal oxidant. This protocol features a wide substrate scope; high functional group tolerance; exclusive chemo-, regio-, and stereoselectivity; and simple, easily available, and inexpensive reaction system. The transformation has demonstrated for the first time that Cu­(OAc)₂ can be renewable after undergoing an oxidative reaction

Ruthenium-Catalyzed Intermolecular Direct Silylation of Unreactive C(sp³)–H Bonds

A Ru-catalyzed intermolecular silylation of unreactive, aliphatic C­(sp³)–H bonds has been described for the first time. This protocol features low catalyst loading, a relatively broad substrate spectrum, good functional group tolerance, and no sensitivity to air, which provides a convenient and practical pathway for the construction of C–Si bonds

Rh(III)-Catalyzed [4 + 1]-Annulation of Azoxy Compounds with Alkynes: A Regioselective Approach to 2<i>H</i>‑Indazoles

A rhodium-catalyzed regioselective C–H activation/cyclization of azoxy compounds with alkynes has been disclosed to construct a variety of 2<i>H</i>-indazoles. A [4 + 1]-cycloaddition rather than a normal [4 + 2] mode is observed in the process of cyclative capture along with an oxygen-atom transfer and a CC triple bond cleavage. This protocol features a broad substrate scope, a good functional group tolerance, and an exclusive regioselectivity

Rh(III)-Catalyzed [4 + 1]-Annulation of Azoxy Compounds with Alkynes: A Regioselective Approach to 2<i>H</i>‑Indazoles

A rhodium-catalyzed regioselective C–H activation/cyclization of azoxy compounds with alkynes has been disclosed to construct a variety of 2<i>H</i>-indazoles. A [4 + 1]-cycloaddition rather than a normal [4 + 2] mode is observed in the process of cyclative capture along with an oxygen-atom transfer and a CC triple bond cleavage. This protocol features a broad substrate scope, a good functional group tolerance, and an exclusive regioselectivity

Nickel-Catalyzed Aminoxylation of Inert Aliphatic C(sp³)–H Bonds with Stable Nitroxyl Radicals under Air: One-Pot Route to α‑Formyl Acid Derivatives

Nickel-catalyzed aminoxylation of an unactivated C­(sp³)–H bond with a stable nitroxyl radical has been accomplished for the first time to offer various <i>N</i>-alkoxyamine derivatives, which further enables a one-pot approach to α-formyl acid derivatives. The aminoxylation process reported also provides direct evidence for the oxidative addition of a cyclometallic intermediate with a free radical, which is helpful for the reaction-mechanism study in transition-metal-catalyzed functionalization of inert C­(sp³)–H bonds