Rh[III]-Catalyzed C–H Amidation Using Aroyloxycarbamates To Give <i>N</i>‑Boc Protected Arylamines

The Rh(III)-catalyzed amidation of C(sp²)–H bonds by the use of electron-deficient aroyloxycarbamates as efficient electrophilic amidation partners is reported. The reaction proceeded under mild conditions with broad functional group tolerance, and pyridine and <i>O</i>-methyl hydroxamic acids serve as efficient directing groups, giving access to valuable <i>N</i>-Boc protected arylamines (also Fmoc and Cbz). Preliminary mechanistic experiments are discussed

Manganese(I)-Catalyzed Direct C–H Allylation of Arenes with Allenes

Polysubstituted allyl groups, for example, the prenyl group, are valuable synthetic handles and widely encountered in bioactive compounds. Reported herein is a manganese­(I)-catalyzed direct C–H coupling with allenes for the efficient assembly of allylated arenes. The protocol offers an extremely high level of atom-economy and is particularly suited for the introduction of 1,1-disubstitiuted allyl groups, as exemplified by the quantitative syntheses of a variety of prenylated indoles. The practicality of this method was evidenced by a gram-scale synthesis with a lower catalyst loading of manganese­(I) (2.5 mol %, 95% yield). Experimental mechanistic studies were conducted, and a possible reaction mechanism was proposed

Mild Rh(III)-Catalyzed C–H Activation and Annulation with Alkyne MIDA Boronates: Short, Efficient Synthesis of Heterocyclic Boronic Acid Derivatives

Taking advantage of Rh­(III)-catalyzed C–H activation reactions, we have developed a mild, short, and efficient method for the synthesis of bench-stable 3-isoquinolone MIDA boronates. The reaction is practical and scalable. The product formed has been applied in the Suzuki–Miyaura reaction with high efficiency. This strategy has also been successfully expanded to the synthesis of MIDA boronate functionalized heterocycles such as isoquinoline, pyrrole, and indole

Mild Mn(OAc)₃‑Mediated Aerobic Oxidative Decarboxylative Coupling of Arylboronic Acids and Arylpropiolic Acids: Direct Access to Diaryl 1,2-Diketones

A simple and efficient method for the synthesis of diaryl 1,2-diketones has been developed. The reaction represents the first example of diaryl 1,2-diketones that are synthesized directly from arylboronic acids and arylpropiolic acids by a radical pathway in moderate to good yields. This reaction proceeds under mild reaction conditions and with good tolerance of a variety of functional groups. Preliminary mechanistic studies were conducted

N–O Bond as External Oxidant in Group 9 Cp*M(III)-Catalyzed Oxidative C–H Coupling Reactions

Group 9 Cp*M­(III) (M = Co, Rh, Ir) complexes have been extensively investigated as catalysts in a variety of C–H activation reactions. Typically, late metal-based silver or copper salt was used (while needed) as oxidant in these catalytic systems. Herein, we report our discovery of a potentially general type of N–O bond-containing oxidants, which allowed the mild and efficient syntheses of isocoumarins, isoquinolines, isoquinolinone, and styrenes via C–H activation catalyzed by group 9 Cp*M­(III) complexes. By using Cp*Rh­(III)-catalyzed isocoumarin synthesis as a model reaction, experimental and theoretical mechanistic studies were conducted. The results concluded that the Rh­(III)–Rh­(I)–Rh­(III) rather than the Rh­(III)–Rh­(V)–Rh­(III) pathway is more likely involved in the mechanism, and both the C–H activation and oxidation of the Cp*Rh­(I) species were involved in the turnover-limiting step

Regioselective Synthesis of 5‑Aminooxazoles via Cp*Co(III)-Catalyzed Formal [3 + 2] Cycloaddition of <i>N</i>‑(Pivaloyloxy)amides with Ynamides

A simple and efficient protocol for the regioselective synthesis of 5-aminooxazoles is disclosed. The reaction, catalyzed by a cheap Cp*Co­(III) catalyst, starts from easily accessible <i>N</i>-(pivaloyloxy)­amides and ynamides. Mild reaction conditions, a broad substrate scope, good functional group tolerance, and good to excellent yields were observed

Cp*Co(III)-Catalyzed Annulations of 2‑Alkenylphenols with CO: Mild Access to Coumarin Derivatives

Cp*Co­(III)-catalyzed annulations of 2-alkenylphenols with CO for the synthesis of coumarin derivatives have been developed. The reaction features mild reaction conditions, broad substrate scope, and good functional group tolerance. Preliminary mechanistic studies were conducted, suggesting that C–H activation is the turnover limiting step. Furthermore, the efficiency of this reaction was demonstrated by the rapid total synthesis of three natural products herniarin, xanthyletin, and seselin

Synthesis of Alkylated Monofluoroalkenes via Fe-Catalyzed Defluorinative Cross-Coupling of Donor Alkenes with <i>gem</i>-Difluoroalkenes

A reductive cross-coupling of <i>gem</i>-difluoroalkenes with diverse unactivated and heteroatom substituted olefins through a Fe-catalyzed hydrogen atom transfer (HAT) strategy is reported. Different from the previous HAT-type olefin cross-coupling reactions, the presence of a fluorine atom in the molecule results in a stereoselective β-F cleavage, leading to a C­(sp²)–C­(sp³) bond formation. A wide variety of alkylated monofluoroalkenes were obtained in good efficiency with excellent <i>Z</i> selectivity under air- and water-tolerant reaction conditions. A similar defluorinative coupling reaction of monofluoroalkenes was also realized

From Indoles to Carbazoles: Tandem Cp*Rh(III)-Catalyzed C–H Activation/Brønsted Acid-Catalyzed Cyclization Reactions

A tandem Cp*Rh­(III)-catalyzed C–H activation/Brønsted acid-catalyzed intramolecular cyclization allows a facile synthesis of carbazoles from readily available indoles. The reaction proceeds under rather mild reaction conditions with the generation of water and N₂ as the only byproducts. Broad substrate scope, excellent functional group tolerance, and high yields were observed. The benzannulation of pyroles for the synthesis of indoles is also feasible using the same protocol

Three-Component Catalytic Carboxygenation of Activated Alkenes Enabled by Bimetallic Rh(III)/Cu(II) Catalysis

A novel cascade Cp*Rh­(III)-catalyzed C–H alkylation/Cu­(II)-promoted α-oxygenation which enabled a three-component carboxygenation of activated alkene is reported. Mild reaction conditions, broad substrate scope, and good functional group tolerance were observed. The synthetic utility of the protocol was showcased by the facile transformations of the product to a variety of structurally diverse molecules. Preliminary mechanistic studies were conducted