Mechanistic snapshots of rhodium-catalyzed acylnitrene transfer reactions
Hoimin Jung, Jeonguk Kweon, Jong‐Min Suh, Mi Hee Lim, Dongwook Kim, Sukbok Chang
IF 45.8
Science
Rhodium (Rh) acylnitrene complexes are widely implicated in catalytic C-H amidation reactions but have eluded isolation and structural characterization. To overcome this challenge, we designed a chromophoric octahedral Rh complex with a bidentate dioxazolone ligand, in which photoinduced metal-to-ligand charge transfer initiates catalytic C-H amidation. X-ray photocrystallographic analysis of the Rh-dioxazolone complex allowed structural elucidation of the targeted Rh-acylnitrenoid and provided firm evidence that the singlet nitrenoid species is primarily responsible for acylamino transfer reactions. We also monitored in crystallo reaction of a nucleophile with the in situ-generated Rh-acylnitrenoid, which provided a crystallographically traceable reaction system to capture mechanistic snapshots of nitrenoid transfer.
Torben Rogge, Nikolaos Kaplaneris, Naoto Chatani, Jinwoo Kim, Sukbok Chang, Benudhar Punji, Laurel L. Schafer, Djamaladdin G. Musaev, Joanna Wencel‐Delord, Charis Amber, Richmond Sarpong, Zoe E. Wilson, Margaret A. Brimble, Magnus J. Johansson, Lutz Ackermann
Selective formation of γ-lactams via C–H amidation enabled by tailored iridium catalysts
Seung Youn Hong, Yoonsu Park, Yeongyu Hwang, Yeong Bum Kim, Mu‐Hyun Baik, Sukbok Chang
IF 45.8
Science
Intramolecular insertion of metal nitrenes into carbon-hydrogen bonds to form γ-lactam rings has traditionally been hindered by competing isocyanate formation. We report the application of theory and mechanism studies to optimize a class of pentamethylcyclopentadienyl iridium(III) catalysts for suppression of this competing pathway. Modulation of the stereoelectronic properties of the auxiliary bidentate ligands to be more electron-donating was suggested by density functional theory calculations to lower the C-H insertion barrier favoring the desired reaction. These catalysts transform a wide range of 1,4,2-dioxazol-5-ones, carbonylnitrene precursors easily accessible from carboxylic acids, into the corresponding γ-lactams via sp<sup>3</sup> and sp<sup>2</sup> C-H amidation with exceptional selectivity. The power of this method was further demonstrated by the successful late-stage functionalization of amino acid derivatives and other bioactive molecules.
Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications
Yoonsu Park, Youyoung Kim, Sukbok Chang
IF 55.8
Chemical Reviews
Catalytic transformation of ubiquitous C-H bonds into valuable C-N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C-H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.
Mechanistic snapshots of rhodium-catalyzed acylnitrene transfer reactions
Hoimin Jung, Jeonguk Kweon, Jong‐Min Suh, Mi Hee Lim, Dongwook Kim, Sukbok Chang
IF 45.8
Science
Rhodium (Rh) acylnitrene complexes are widely implicated in catalytic C-H amidation reactions but have eluded isolation and structural characterization. To overcome this challenge, we designed a chromophoric octahedral Rh complex with a bidentate dioxazolone ligand, in which photoinduced metal-to-ligand charge transfer initiates catalytic C-H amidation. X-ray photocrystallographic analysis of the Rh-dioxazolone complex allowed structural elucidation of the targeted Rh-acylnitrenoid and provided firm evidence that the singlet nitrenoid species is primarily responsible for acylamino transfer reactions. We also monitored in crystallo reaction of a nucleophile with the in situ-generated Rh-acylnitrenoid, which provided a crystallographically traceable reaction system to capture mechanistic snapshots of nitrenoid transfer.
Torben Rogge, Nikolaos Kaplaneris, Naoto Chatani, Jinwoo Kim, Sukbok Chang, Benudhar Punji, Laurel L. Schafer, Djamaladdin G. Musaev, Joanna Wencel‐Delord, Charis Amber, Richmond Sarpong, Zoe E. Wilson, Margaret A. Brimble, Magnus J. Johansson, Lutz Ackermann
Selective formation of γ-lactams via C–H amidation enabled by tailored iridium catalysts
Seung Youn Hong, Yoonsu Park, Yeongyu Hwang, Yeong Bum Kim, Mu‐Hyun Baik, Sukbok Chang
IF 45.8
Science
Intramolecular insertion of metal nitrenes into carbon-hydrogen bonds to form γ-lactam rings has traditionally been hindered by competing isocyanate formation. We report the application of theory and mechanism studies to optimize a class of pentamethylcyclopentadienyl iridium(III) catalysts for suppression of this competing pathway. Modulation of the stereoelectronic properties of the auxiliary bidentate ligands to be more electron-donating was suggested by density functional theory calculations to lower the C-H insertion barrier favoring the desired reaction. These catalysts transform a wide range of 1,4,2-dioxazol-5-ones, carbonylnitrene precursors easily accessible from carboxylic acids, into the corresponding γ-lactams via sp<sup>3</sup> and sp<sup>2</sup> C-H amidation with exceptional selectivity. The power of this method was further demonstrated by the successful late-stage functionalization of amino acid derivatives and other bioactive molecules.
Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications
Yoonsu Park, Youyoung Kim, Sukbok Chang
IF 55.8
Chemical Reviews
Catalytic transformation of ubiquitous C-H bonds into valuable C-N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C-H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.
Mechanistic evaluations of photocatalytic access to N‐centered radicals and nitrenoids
Hoimin Jung, Jeonguk Kweon, Sukbok Chang
IF 2.2
Bulletin of the Korean Chemical Society
Abstract Recent advances in photocatalytic organic transformations have enabled new bond formations that are otherwise challenging under thermal reaction conditions. Among these, significant progress has been achieved especially in amination reactions by harnessing the reactivity of nitrogen‐centered radicals or organic nitrene species, generated from various prefunctionalized amino group precursors, through photoinduced single‐electron transfer (SET) or triplet–triplet energy transfer (TTEnT). Although plausible mechanisms leading to the reactive nitrogen‐centered intermediate have been proposed, a detailed depiction of the electron flow during the photoinduced process would be highly intriguing. In this study, we employed computational intrinsic bond orbital (IBO) analysis to illustrate the electron relocations during the activation of several types of aminating precursors into nitrogen‐centered radicals or organic nitrenes. Our quantum chemical investigations provide critical mechanistic insights into the nitrogen‐centered reactive intermediate formation, offering foundations for designing photocatalytic amination strategies.
Catalytic Amino Group Transfer Reactions Mediated by Photoinduced Nitrene Formation from Rhodium‐Hydroxamates
Hoimin Jung, Jeonguk Kweon, Jong‐Min Suh, Andrés Arribas, Dongwook Kim, Mi Hee Lim, Sukbok Chang
Angewandte Chemie
Abstract Herein, we report a photocatalytic platform to access transient nitrenoids by designing photo‐responsive neutral rhodium‐hydroxamate complexes. Combined experimental and computational mechanistic studies, including electron paramagnetic resonance (EPR) and mass spectrometric analysis, suggest that electrophilic Fischer‐type Rh‐acylnitrenoid intermediates could be generated via photoactivation of corresponding Rh‐hydroxamates via N‐O bond homolysis and redox event. Moreover, catalytic acylnitrenoid transfer was explored toward the amidation of various hydrocarbons, amines, and alcohols to furnish new N−C, N−N, and N−O bonds.
Regioselective Formal β-C(sp<sup>3</sup>)–H Amidation of Ketones by Merging Photocatalysis and Ni-Nitrenoid Transfer
Hyeyun Keum, Harin Ryoo, Dongwook Kim, Sukbok Chang
IF 5
Organic Letters
β-Amino carbonyls are synthetically valuable scaffolds that are prevalent in bioactive molecules and pharmaceuticals, yet efficient and selective methods for their synthesis remain underdeveloped. Disclosed herein is a dual photoredox/nickel-catalyzed platform for the formal β-C(sp<sup>3</sup>)-H amidation of ketones to access β-amido ketones. The method enables the regioselective β-amidation of both cyclic and linear ketones under mild conditions, employing silyl enol ethers and dioxazolones as readily available coupling partners. Mechanistic studies support the involvement of a photogenerated allylic carbon radical, which engages with Ni-nitrenoid species to facilitate C(sp<sup>3</sup>)-N bond formation.
Regioselective Hydroamidation of α,β-Unsaturated Esters Enabled by Lewis Acid/Iron Relay Catalysis
Hoonchul Choi, Dongwook Kim, Sukbok Chang
IF 15.6
Journal of the American Chemical Society
Achieving precise regioselectivity in the hydroamination of alkenes is in high demand yet remains a longstanding challenge, particularly when electronically competing β-substituents are present. Here, we report a dual boron/iron catalytic system that enables the unprecedented hydroamidation of α,β-unsaturated esters to exclusively access α-amidated esters under mild conditions. The strategy harnesses the Lewis acidity of B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> to rapidly generate reactive silyl ketene acetal intermediates, which are subsequently intercepted by in situ generated iron nitrenoids. Central to this cooperative activation mode is the dual role of the chloride anion in modulating both boron and iron catalytic reactivity. This protocol is operationally simple, requiring no tailored ligands, light, or electrochemical setup, and proceeds efficiently with only 1 mol % of boron and iron catalysts. The system exhibits a broad scope of unsaturated esters, tolerating β-aryl, -alkyl, -silyl, -perfluoroalkyl, and -boryl groups. This work lays the foundation for universal α-selective hydrofunctionalization strategies across electronically complex substrates.
Post-functionalization of polyethers by photoinduced C–H amidation via polar-radical relay
Seung Beom Baek, Youngho Kim, Wongyu Lee, Sangwon Seo, Dongwook Kim, Myungeun Seo, Sukbok Chang
IF 15.7
Nature Communications
The C-H functionalization of polymers enables the direct incorporation of new functional groups into polymer backbones, presenting significant opportunities for the upcycling of commodity polymers. However, developing reactions that achieve selective functionalization while preserving the intrinsic features of polymers and avoiding undesirable structure deformation remains a considerable challenge. In this study, we present a transition metal-free post-functionalization approach for polyethers via a photoinduced α-C-H amidation reaction. This strategy provides a route to previously unattainable α-amino polyethers, which exhibit distinct physical properties from those of the parent polymer. By leveraging a polar-radical relay mechanism, we effectively incorporate C-N bonds into the polyether backbone while suppressing degradation and cross-linking. Conducted under mild and convenient conditions, this approach demonstrates significant site selectivity at the ethereal α-position, even in the presence of other types of C-H bonds, achieving tailed post-functionalization of macromolecules. Furthermore, the present strategy holds promise for broader applications, including the amidative degradation of commodity polymers and transformation of polyethylene glycol (PEG) network.
