Cobalt-Catalyzed Four-Component Carbonylation of Methylarenes with Ethylene and Alcohols

Single-Electron-Transfer-Mediated Carbonylation Reactions

ConspectusTransition-metal-catalyzed carbonylation coupling methods have been accepted as an essential tool for producing carbonylated products over the past few decades. Despite its long-standing history and widespread industrial applications, several challenges remain in carbonylation chemistry. These include reliance on precious metal catalysts, the need of high-energy radiation, difficulties in carbonylation of unactivated chemical bonds, etc. As an alternative to classic two-electron transfer process, single-electron-transfer (SET)-mediated carbonylation has emerged as a powerful tool to achieve elusive carbonylation transformations. Over the past few years, carbonylation of commonly available functional handles, such as alkenes and alkyl halides, via the single-electron pathway has emerged as a valuable area of research.Our team has been dedicated to developing new carbonylation reactions using bulk chemicals to construct high-value carbonylated products. These reactions have broad synthetic and industrial applications, motivating us to explore SET-mediated carbonylation transformations for two key classes of bulk chemicals: alkanes and alkyl halides. Specifically, our work has centered on two main approaches: (1) Single-electron reduction of C(sp3)-X bonds: this strategy leverages single-electron reduction to activate C(sp3)-X bonds, promoting the formation of carbon radicals, which in turn promotes subsequent addition to metals or CO. However, a significant challenge lies in the highly negative reduction potential of certain substrates [Ered < -2 V compared to the saturated calomel electrode (SCE) for unactivated alkyl iodides]. Despite these challenges, the intrinsic reducibility of CO and the reactivity of various carbonyl-metal intermediates facilitate smooth reaction progress. (2) Single-electron oxidative of C(sp3)-H bonds: this strategy emphasizes efficiency, high atomic utilization, and minimal waste by bypassing traditional preactivation methods. Using 3d metal catalysts, we have successfully performed aminocarbonylation and alkoxycarbonylation on a wide range of C(sp3)-H bonds (such as those in aliphatic alkanes, ethers, amines, etc.). The above two approaches also enabled radical relay carbonylation of alkenes, allowing precise control over reaction intermediates and pathways. Such control improves both reaction efficiency and selectivity. These advancements have enabled transition metal or photoredox catalysis to facilitate radical relay carbonylation of unactivated alkenes, resulting in transformations such as oxyalkylative carbonylation, aminoalkylative carbonylation, fluoroalkylative carbonylation, double carbonylation, and rearrangement carbonylation.SET-mediated carbonylation significantly enhances the sustainability and scalability of the carbonylation process by reducing reliance on precious metal catalysts and enabling milder reaction conditions. Additionally, by carefully controlling reaction intermediates, we have fine-tuned the process to produce a wide range of carbonylation products with high selectivity. This flexibility expands the applications of carbonylation in synthetic chemistry and industrial processes. Finally, we place particular emphasis on the application of carbonylation reactions in drug discovery, where they serve as powerful functional handles for the late-stage modification of bioactive molecules. The broad applicability of SET-mediated carbonylation methods to various chemical bonds significantly enriches the toolbox for drug synthesis, enabling the efficient functionalization of complex molecules. This versatile approach has the potential to accelerate the discovery of novel therapeutic agents, making it a critical tool in modern medicinal chemistry.

Mechanistic Insights into the Palladium-Catalyzed Perfluoroalkylative Carbonylation of Unactivated Alkenes to β-Perfluoroalkyl Esters: A DFT Study

Transition metal-catalyzed multicomponent carbonylation is an efficient synthetic strategy to access multifunctional esters in high yields with broad functional group tolerance and good chemoselectivity. Considering the development of highly efficient synthetic methods for esters, it remains significant to grasp the mechanism of constructing multifunctional esters. Herein, density functional theoretical calculations were carried out to acquire mechanistic insight into the synthesis of β-perfluoroalkyl esters from a specific palladium-catalyzed perfluoroalkylative carbonylation of unactivated alkenes using carbon monoxide. A detailed mechanistic understanding of this reaction route includes (1) multistep radical reaction process, (2) C-C coupling and CO insertion, (3) ligand exchange, and (4) Pd-based intermediate oxidation and reductive elimination. The multistep radical process was fundamentally rationalized, including Rf· formation and radicals A and E from unactivated alkene and CO oxidation, respectively. The potential energy calculation indicated that the CO insertion into the perfluorinated alkyl radicals preceded Pd-catalyzed oxidation in the competitively multistep free radical reaction process. In addition, the I-/PhO- exchange step was predicted to be spontaneous to products. The IGMH analysis further attested to the reductive elimination process involved in the rate-determining step. Thus, a simple and valid density functional theory (DFT) approach was developed to reveal the multistep radical mechanism for the Pd-catalyzed perfluoroalkylative carbonylation of unactivated alkenes to access functional β-perfluoroalkyl esters.

Cobalt-Catalyzed Carbonylative Synthesis of 4-Oxobutanoates from Formamide and Ethylene

The direct concurrent installation of amide and ester groups across olefin motifs represents a powerful and promising functionalization tool in organic chemistry. Herein, a ligand-free cobalt-catalyzed four-component radical relay carbonylative difunctionalization of ethylene for the synthesis of 4-oxobutanoates has been developed. Valuable C4 building blocks were produced in a highly atom-economical fashion.

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.

The recent advances in cobalt-catalyzed C(sp3)-H functionalization reactions

Over the past decades, reactions involving C-H functionalization have become a hot theme in organic transformations because they have a lot of potential for the streamlined synthesis of complex molecules. C(sp³)-H bonds are present in most organic species. Since organic molecules have massive significance in various aspects of life, the exploitation and functionalization of C(sp³)-H bonds hold enormous importance. In recent years, the first-row transition metal-catalyzed direct and selective functionalization of C-H bonds has emerged as a simple and environmentally friendly synthetic method due to its low cost, unique reactivity profiles and easy availability. Therefore, research advancements are being made to conceive catalytic systems that foster direct C(sp³)-H functionalization under benign reaction conditions. Cobalt-based catalysts offer mild and convenient reaction conditions at a reasonable expense compared to conventional 2^nd and 3^rd-row transition metal catalysts. Consequently, the probing of Co-based catalysts for C(sp³)-H functionalization is one of the hot topics from the outlook of an organic chemist. This review primarily focuses on the literature from 2018 to 2022 and sheds light on the substrate scope, selectivity, benefits and limitations of cobalt catalysts for organic transformations.

Non-Noble Metal-Catalyzed Carbonylative Multi-Component Reactions

Carbonylative multi-component reactions (CMCR), having four or more kinds of starting materials, provide an efficient strategy for the preparation of polyfunctional carbonylated compounds. Diverse CMCR utilizing non-noble transition-metal catalysts have been developed. This review summarized and discussed the recent advances in non-noble metal-catalyzed carbonylative multi-component reactions.