Synthesis of Isoindolinones by Pd-Catalyzed Coupling between N-Methoxybenzamide and Styrene Derivatives

Palladium(II)/Lewis acid catalyzed oxidative olefination of 2-benzamidopyridine 1-oxide with acrylates: synthesis of isoindolinones

A palladium(II)/Lewis acid-catalyzed C-H olefination of 2-benzamidopyridine 1-oxide with acrylates followed by intramolecular aza-Michael addition for the synthesis of isoindolinones has been developed. The use of a heterobimetallic Pd(II)/Cu(II) catalyst enhances the efficiency of the reaction, enabling the synthesis of a potential anti-sedative agent.

Ru(II)-Catalyzed Redox-Neutral C-H Olefination and Tandem Cyclization with Vinyl Sulfones: Leveraging Sulfinate Anion as a Leaving Group for the Synthesis of 3-Methyleneisoindolin-1-ones

We developed a Ru(II)-catalyzed redox-neutral C-H olefination of N-methoxybenzamides with vinyl sulfones. The reaction is operationally simple and conducted at ambient temperature and does not require silver additives or external oxidants, making it suitable for late-stage functionalization. Notably, we leveraged the leaving group ability of sulfinate anion to synthesize 3-methyleneisoindolin-1-ones through a tandem C-H olefination/cyclization/elimination sequence at ambient temperature. Moreover, we successfully demonstrated the synthetic versatility of 3-methyleneisoindolin-1-one for the construction of an isoindolobenzazepine core.

Isoindolinone synthesis through Rh/Cu-catalyzed oxidative C-H/N-H annulation of N-methoxy benzamides with saturated ketones

The synthesis of isoindolinones from N-methoxy benzamides and saturated ketones via a bimetallic tandem catalytic annulation has been accomplished. The reaction is catalyzed by a Rh/Cu-cocatalytic system and proceeds via the combination of Cu-catalyzed dehydrogenation of ketones and Rh-catalyzed direct C-H functionalization with the assistance of the N-methoxy amide group which also acts as an oxidant to regenerate the Rh catalyst. This method shows good compatibility with a wide range of substrates and functional groups, and provides an alternative strategy to obtain diverse isoindolinones.

Construction of aziridine, azetidine, indole and quinoline-like heterocycles via Pd-mediated C-H activation/annulation strategies

N-Heterocycles can be found in natural products and drug molecules and are indispensable components in the area of organic synthesis, medicinal chemistry and materials science. The construction of these N-containing heterocycles by traditional methods usually requires the preparation of reactive intermediates. In the past decades, with the rapid growth of transition metal catalysed coupling reactions, syntheses of heterocycles from precursors with inert chemical bonds have become a challenge. More recently, in the field of transition metal associated C-H direct functionalization, efficient methods have been developed for the syntheses of N-heterocyclic compounds such as aziridines, azetidines, indoles and quinolines under the click type of reaction mode. In this review, representative synthetic methodologies developed in the recent 10 years for the preparation of this small class of N-heterocycles via the Pd-catalysed C-H activation and C-N bond formation pathway are discussed. We hope this article will provide new insights from the strategies highlighted into future molecular design, synthesis and applications in medical and materials sciences.

Pd-Catalyzed C(sp2)-H olefination: synthesis of N-alkylated isoindolinone scaffolds from aryl amides of amino acid esters

Isoindolinone is a constituent of various natural products and synthetic biologically active compounds. The classical multi-step synthetic methods used to prepare various indolinone derivatives are tedious and challenging. One-pot synthetic methods are attractive and economical. Transition-metal-catalyzed C-H activation is an emerging tool for synthesizing natural products and small organic molecules via reducing the number of synthetic steps necessary. This paper describes the synthesis of N-alkyl-3-methenyl chiral isoindolinone derivatives from aryl amides of L-amino acids and non-activated alkene via Pd-catalyzed C(sp²)-H olefination. Herein, the amino acid residue acts as a directing group for olefination at the aryl ring, and then cyclization occurs at the amide NH. Hence, this methodology could be helpful to transform standard amino acids into respective chiral isoindolinone derivatives.

Facile Synthesis of Alkylidene Phthalides by Rhodium-Catalyzed Domino C-H Acylation/Annulation of Benzamides with Aliphatic Carboxylic Acids

The Rh-catalyzed ortho-C(sp² )-H functionalization of 8-aminoquinoline-derived benzamides with aliphatic acyl fluorides generated in situ from the corresponding acids has been developed. This reaction initiated with 8-aminoquinoline-directed ortho-C(sp² )-H acylation, which was accompanied by subsequent intramolecular nucleophilic acyl substitution of amide group to produce alkylidene phthalides This approach exhibits high stereo-selectivity for Z-isomer products, and tolerates a variety of functional groups as well as aliphatic carboxylic acids with diverse structural scaffolds.

A Bridge to Alkaloid Synthesis

The construction of a structurally rigid architecture with chiral complexity, necessary to enhance the interaction with binding sites of drug targets, has been adapted as an intriguing approach in drug development. In the past few years, we have been interested in the synthesis of biologically significant and bridged alkaloids via novel synthetic methods and strategies based on recognition of the privileged pattern. Therefore, nitroso-ene and aza-Wacker cyclizations were elevated for the first time to construct bridged alkaloids, such as hosieine A, kopsone, melinonine-E and strychnoxanthine. Mechanistic investigations, including computational calculations for nitroso-ene reaction and deuterated experiments for aza-Wacker reaction, enable us to gain more insights into the chemical reactivity and selectivity of specific functional groups in developing viable synthetic methods.

Isoindolinone Synthesis via One-Pot Type Transition Metal Catalyzed C-C Bond Forming Reactions

Isoindolinone structure is an important privileged scaffold found in a large variety of naturally occurring as well as synthetic, biologically and pharmaceutically active compounds. Owing to its crucial role in a number of applications, the synthetic methodologies for accessing this heterocyclic skeleton have received significant attention during the past decade. In general, the synthetic strategies can be divided into two categories: First, direct utilization of phthalimides or phthalimidines as starting materials for the synthesis of isoindolinones; and second, construction of the lactam and/or aromatic rings by different catalytic methods, including C-H activation, cross-coupling, carbonylation, condensation, addition and formal cycloaddition reactions. Especially in the last mentioned, utilization of transition metal catalysts provides access to a broad range of substituted isoindolinones. Herein, the recent advances (2010-2020) in transition metal catalyzed synthetic methodologies via formation of new C-C bonds for isoindolinones are reviewed.

Rhodium-Catalyzed Electrooxidative C-H Olefination of Benzamides

Metal-catalyzed chelation-assisted C-H olefinations have emerged as powerful tools for the construction of functionalized alkenes. Herein, we describe the rhoda-electrocatalyzed C-H activation/alkenylation of arenes. The olefinations of challenging electron-poor benzamides were thus accomplished in a fully dehydrogenative fashion under electrochemical conditions, avoiding stoichiometric chemical oxidants, and with H2 as the only byproduct. This versatile alkenylation reaction also features broad substrate scope and used electricity as a green oxidant.

Palladium(II)/Lewis Acid-Catalyzed Oxidative Olefination/Annulation of N-Methoxybenzamides: Identifying the Active Intermediates through NMR Characterizations

Although Pd(II)-catalyzed C-H activation in arenes has been widely successful in organic synthesis with many palladacycle compounds isolated as the intermediates in ligand-directed C-H activation, direct identification of the reaction intermediates such as the π-complex prior to the C-H activation is still not successful because of their instability. In the present study, we introduce a Pd(II)/LA (LA: Lewis acid)-catalyzed oxidative olefination/annulation reaction between N-methoxybenzamides and acrylates with oxygen as the oxidant source, in which two intermediates, including an unsymmetrical η⁶-complex and a palladacycle species without the proton releasing to the environment, were identified through NMR characterizations. The in situ formation of the heterobimetallic Pd(II)/LA species such as Pd(II)/Sc(III) may have enhanced the electrophilic properties of the Pd²⁺ cation, thus improving the stability of the π-complex, herein, an unsymmetrical η⁶-complex, and improving its catalytic efficiency. The observed insensitive electronic effect preferred the concerted metalation-deprotonation (CMD) mechanism for this C-H activation, and the detected palladacycle intermediate without the proton releasing to the environment offered an experimental clue to support the proposed CMD mechanism.

Rhodium-Catalyzed ortho-Olefination of Sterically Demanding Benzamides: Application to the Asymmetric Synthesis of Axially Chiral Benzamides

It has been established that an unsubstituted cyclopentadienyl rhodium(III) (CpRh^III ) complex is a highly active catalyst for the aerobic oxidative ortho C-H bond olefination of sterically demanding ortho-substituted benzamides with alkenes. This catalysis was successfully applied to the diastereoselective synthesis of axially chiral N,N-dialkylbenzamides. The combination of the ruthenium(II)-catalyzed enantioselective hydrogenation and the CpRh^III -catalyzed diastereoselective ortho C-H bond olefination enabled the asymmetric synthesis of axially chiral N,N-dialkylbenzamide derivatives with high ee values.

Synthesis of Lactams via Ir-Catalyzed C-H Amidation Involving Ir-Nitrene Intermediates

x-membered lactams were synthesized via either an amidation of sp³ C-H bonds or an electrophilic substitution of arenes via Ir-nitrene intermediates. With the employment of a readily available iridium catalyst in dichloromethane or hexafluoro-2-propanol, a wide range of lactams were synthesized in good to excellent yields with high selectivity.

Revisiting the mechanism of the Fujiwara–Moritani reaction

A new perspective of the Fujiwara–Moritani reaction is presented, including its kinetic profile and catalyst deactivation studies.

Mechanism of Rhodium(III)-Catalyzed C-H Activation/Annulation of Aromatic Amide with α-Allenol: A Computational Study

With the help of DFT calculations, the reaction mechanisms of the rhodium(III)-catalyzed C-H activation/annulation between aromatic amide and α-allenol leading to the formation of isoindolinone have been theoretically investigated. Our calculated results show that the catalytic cycle consists of four stages: N-H deprotonation and C-H activation (Stage I), allene insertion, rearrangement and isomerization (Stage II), β-H elimination and enol-keto tautomerism (Stage III), and catalyst regeneration resulting in the five-membered ring product (Stage IV). For stage IV, besides the reaction paths proposed by the experimentalists, i.e., the insertion and reductive elimination (labeled as path a) and the reductive elimination and hydroamination (labeled as path b), an alternative path which involves C-N and C-H reductive eliminations (labeled as path c) was proposed and examined. The computational results show that the newly established path c is more energetically favorable than the reaction paths proposed by the experimentalists (paths a and b). The allene (non-terminal double bond) insertion step contributes to the rate-determining step with an overall activation free energy of 24.6 kcal/mol. Our study is beneficial for a better comprehension of the reaction mechanisms and provides a significant suggestion for further development of similar reactions.

Aerobic Oxidative Olefination of Benzamides with Styrenes Catalyzed by a Moderately Electron-Deficient CpRh(III) Complex with a Pendant Amide

It has been established that a newly developed moderately electron-deficient cyclopentadienyl (Cp)-Rh(III) complex, bearing ester and pendant amide moieties on the Cp ring [Cp^ARh(III)], is able to catalyze the aerobic oxidative olefination of benzamides, bearing nonspecial carbamoyl groups, with styrenes including disubstituted ones at relatively low temperature (60-80 °C). The presence of both the ester and pendant acidic N-phenylcarbamoyl moieties on the Cp^A ligand play important roles in facilitation of the catalysis without sacrificing thermal stability of the complex.

Palladium-catalyzed annulation of N-alkoxy benzsulfonamides with arynes by C–H functionalization: access to dibenzosultams

Palladium-catalyzed C–H/N–H functionalization of N-alkoxy benzsulfonamides with arynes provides dibenzosultams via C–C/C–N bond formation, accompanied by an unexpected N–O bond cleavage.

Intramolecular Palladium-Catalyzed Oxidative Amination of Furans: Synthesis of Functionalized Indoles

Unconventional modification of palladium-catalyzed oxidative amination where a furan ring serves as a masked olefin is described. The designed chemical process provides 2-(2-acylvinyl)indole derivatives with up to a 93% yield and excellent E-selectivity. A highly reactive α,β-unsaturated carbonyl moiety of the obtained compounds allows for accessing various heteroaromatic scaffolds through simple synthetic procedures.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Recent advances in transition-metal catalyzed positional-selective alkenylations via twofold C–H activation directed by removable or traceless directing groups are reviewed.

Heteroannulation enabled by a bimetallic Rh(iii)/Ag(i) relay catalysis: application in the total synthesis of aristolactam BII

A Rh(iii)/Ag(i) relay catalysis allowed the construction of 3-alkylidene isoindolinones and 3-alkylidene isobenzofuranones. The synthetic application in the total synthesis was accomplished.