Tuning the Oxidative Mono- or Double-Carbonylation of Alkanes with CO by Choosing a Co or Cu Catalyst

Palladium-Catalyzed Four-Component Radical Cascade Carbonylation Access to 2,3-Disubstituted Benzofuran Derivatives

Multicomponent radical tandem reactions have emerged as a crucial technique for synthesizing complex molecules in organic chemistry. In this study, we report a palladium-catalyzed four-component difluoroalkylative carbonylation of enynes and ethyl difluoroiodoacetate. This transformation proceeds through a multistep sequential reaction that introduces reactive difluoro and carbonyl groups while constructing the benzofuran skeleton. Moreover, a variety of valuable 2,3-disubstituted benzofuran derivatives were obtained in respectable yields with excellent functional group compatibility.

De Novo Synthesis of α-Ketoamides via Pd/TBD Synergistic Catalysis

Precisely controlling the product selectivity of a reaction is an important objective in organic synthesis. α-Ketoamides are vital intermediates in chemical transformations and privileged motifs in numerous drugs, natural products, and biologically active molecules. The selective synthesis of α-ketoamides from feedstock chemicals in a safe and operationally simple manner under mild conditions is a long-standing catalysis challenge. Herein, an unprecedented TBD-switched Pd-catalyzed double isocyanide insertion reaction for assembling ketoamides in aqueous DMSO from (hetero)aryl halides and pseudohalides under mild conditions is reported. The effectiveness and utility of this protocol are demonstrated by its diverse substrate scope (93 examples), the ability to late-stage modify pharmaceuticals, scalability to large-scale synthesis, and the synthesis of pharmaceutically active molecules. Mechanistic studies indicate that TBD is a key ligand that modulates the Pd-catalyzed double isocyanide insertion process, thereby selectively providing the desired α-ketoamides in a unique manner. In addition, the imidoylpalladium(II) complex and α-ketoimine amide are successfully isolated and determined by X-ray analysis, confirming that they are probable intermediates in the catalytic pathway.

Metal-Free Bisamidation of N-Tosylhydrazones with Carboxylic Acids Promoted by Tetrabutylammonium Iodide and tert-Butyl Hydroperoxide

A versatile reaction between N-tosylhydrazones and carboxylic acids to access bisamides is reported. This metal-free, room-temperature reaction was catalyzed by TBAI, while TBHP served as the oxidant. Broad substrate scope and good functional group tolerance are the key features of the strategy. Subsequent intramolecular N-arylation of suitably substituted bisamides readily afforded functionalized 3-indazolones.

Atmospheric Oxygen Facilitated Oxidative Amidation to α-Ketoamides and Unusual One Carbon Degradative Amidation to N-Alkyl Amides

A mild, transition-metal-free novel synthetic approach for the construction of C═O and C-N bonds has been demonstrated. Easily accessible gem-dibromoalkenes under similar conditions form oxidative amidation product α-ketoamides and unusual degradative amidation product N-alkyl amides by simply changing the amine substitute. Atmospheric air containing molecular oxygen proved to be an ideal oxidant for an amidation reaction. Under similar conditions, the electron-deficient gem-dibromoalkenes play a dual role with different formamides forming novel oxidative amidation products and by the state of art neighboring group participation of amine to unusual one-carbon degradative amidation products.

Electrochemical Oxidative Carbonylation of NH-Sulfoximines

The electrochemical synthesis of N-aroylsulfoximines features the use of tetra-n-butylammonium iodide (TBAI) as the medium and a broad substrate scope, thus affording a wide range of N-aroylated sulfoximines in moderate to good yields. The advantages of this electrochemical strategy are augmented by mild reaction conditions that are external oxidant-free, ligand-free, and easy to scale up to gram scale. Both the control experiments and the mechanistic studies revealed that the whole electrochemical process proceeded through a palladium (II/IV/II) catalytic cycle.

Photoinduced Five-Component Radical Relay Aminocarbonylation of Alkenes

Radical single carbonylation reactions with CO constitute a direct and robust strategy toward various carbonyl compounds from readily available chemicals, and have been extensively studied over the past decades. However, realizing highly selective catalytic systems for controlled radical double carbonylation reactions has remained a substantial challenge, particularly for the more advanced multicomponent variants, despite their great potential value. Herein, we report a visible-light-driven radical relay five-component radical double aminocarbonylation reaction of unactivated alkenes using CO under metal-free conditions. This protocol provides direct access to valuable γ-trifluoromethyl α-ketoamides with good yields and high chemoselectivity. Crucial was the identification of distinct dual roles of amine coupling partners, sequentially acting as electron donors for the formation of photoactive electron donor-acceptor (EDA) complexes with radical precursors and then as a CO acceptor via nitrogen radical cations to form carbamoyl radicals. Cross-coupling of carbamoyl radicals with the acyl radicals that are formed in an alkene-based relay process affords double aminocarbonylation products.

Regioselective C-H Active Carbonylation via 1,4-Palladium Migration

We report a highly regioselective three-component coupling reaction of styrene, CO gas, and an amine compound to synthesize multisubstituted α,β-unsaturated amides, which involves a palladium-catalyzed sequential 1,4-palladium migration, C(sp²)-H activation, carbonylation, and amination. Salient features of this strategy include the use of 1 atm of CO, excellent stereochemistry, and good functional group tolerance. Further, a series of control experiments and density functional theory calculations were performed to afford some insights for the transfer mechanism.

Palladium-Catalyzed Carbonylations: Application in Complex Natural Product Total Synthesis and Recent Developments

Carbon monoxide is a cheap and abundant C1 building block that can be readily incorporated into organic molecules to rapidly build structural complexity. In this Perspective, we outline several recent (since 2015) examples of palladium-catalyzed carbonylations in streamlining complex natural product total synthesis and highlight the strategic importance of these carbonylation reactions in the corresponding synthesis. The selected examples include spinosyn A, callyspongiolide, perseanol, schizozygane alkaloids, cephanolides, and bisdehydroneostemoninine and related stemona alkaloids. We also provide our perspective about the recent advancements and future developments of palladium-catalyzed carbonylations.

Palladium-Catalyzed Reductive Double Carbonylation of Nitroarenes with Aryl Halides Using Mo(CO)6 as a Reductant and Carbonyl Source

A new palladium-catalyzed reductive double carbonylation of nitroarenes with aryl halides for the synthesis of benzoxazin-4-ones has been reported. The key to success was the use of Mo(CO)₆ as a reductant and bench-stable solid carbonyl sources. Various aryl iodides, bromides, and trifluoromethanesulfonates are suitable reaction partners and produce corresponding benzoxazin-4-one derivatives in moderate to good yields. Preliminary mechanistic studies indicate that nitrosoarene was first generated as the key intermediate through nitro reduction. Remarkably, this method avoids the use of toxic CO gas and is further applied to the late-stage modification of estrone.

Recent advances in Cu-catalyzed carbonylation with CO

Transition metal-catalyzed carbonylation has emerged as a powerful and versatile strategy for the efficient construction of complicated carbonyl-containing molecules from simple chemical feedstocks in the past decades.