Palladium-catalyzed carbo-heterofunctionalization of alkenes for the synthesis of oxindoles and spirooxindoles

Photoinduced radical cascade domino Heck coupling of N-aryl acrylamide with vinyl arenes enabled by palladium catalysis

Here, a redox-neutral palladium-catalyzed photo-induced radical cascade domino Heck reaction of N-aryl acrylamide with vinyl arenes is described. A diverse range of bioactive oxindoles, featuring an all-carbon quaternary center, were synthesized. The reaction is proposed to proceed via an open-shell intermediate and occurs under mild reaction conditions, exhibiting excellent functional group tolerance. Importantly, the synthesized products can be readily transformed into biologically active molecules, including (±)-physostigmine and (±)-physovenine.

TBHP-mediated photochemical coupling/cyclization of N-arylacrylamides with thiols

The effective photoredox-mediated oxidative thiolation and cyclization of N-arylacrylamides with thiols leads to biologically interesting 3-thionated oxindoles through C-S and C-C bond formation. This process represents a straightforward reaction that starts from non-prefunctionalized thiolating reagents. Mechanistic studies demonstrated that the TBHP serves as a key radical initiator with visible-light catalysis.

Copper-Catalyzed Hydrogen Atom Transfer and Aryl Migration Strategy for the Arylalkylation of Activated Alkenes

Herein, we describe the copper-catalyzed arylalkylation of activated alkenes via hydrogen-atom transfer and aryl migration strategy. The reaction was carried out through a radical-mediated continuous migration pathway using N-fluorosulfonamides as the alkyl source. The primary, secondary, and tertiary alkyl radicals formed by intramolecular hydrogen-atom transfer proceeded smoothly. This methodology is an efficient approach for the synthesis of various amide derivatives possessing a quaternary carbon center with good yields and high regioselectivity.

Palladium-Catalyzed Organic Reactions Involving Hypervalent Iodine Reagents

The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C—H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C—H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.

Synthesis of 3-substituted 2-oxindoles from secondary α-bromo-propionanilides via palladium-catalyzed intramolecular cyclization

In contrast to aromatic halides, coupling reactions involving oxidative addition of alkyl halides, especially secondary or tertiary halides, to transition metals tend to be more challenging. Herein a palladium-catalyzed intramolecular cyclization of α-bromo-propionanilides has been developed, delivering a series of 3-substituted 2-oxindoles in high yields. The method features easy to prepare starting materials, broad substrate scope and excellent functional group tolerance. A detailed mechanistic investigation has been performed.

TCCA-mediated oxidative rearrangement of tetrahydro-β-carbolines: facile access to spirooxindoles and the total synthesis of (±)-coerulescine and (±)-horsfiline

Multi-reactive centered reagents are beneficial in chemical synthesis due to their advantage of minimal material utilization and formation of less by-products. Trichloroisocyanuric acid (TCCA), a reagent with three reactive centers, was employed in the synthesis of spirooxindoles through the oxidative rearrangement of various N-protected tetrahydro-β-carbolines. In this protocol, low equivalents of TCCA were required to access spirooxindoles (up to 99% yield) with a wide substrate scope. Furthermore, the applicability and robustness of this protocol were proven for the gram-scale total synthesis of natural alkaloids such as (±)-coerulescine (1) and (±)-horsfiline (2) in excellent yields.

Three-reactive centered reagent (TCCA) mediated construction of spirooxindoles through an oxidative rearrangement of various N-protected tetrahydro-β-carbolines and total synthesis of natural alkaloids (±)-coerulescine and (±)-horsfiline.

Transition metal-catalyzed synthesis of spirooxindoles

Spirooxindole is a principal bioactive agent and is observed in several natural products including alkaloids. They are broadly studied in the pharmaceutical field and have a significant role in the evolution of drugs such as anti-viral, anti-cancer, anti-microbial etc. In organic chemistry, an indispensable role is presented by transition metal catalysts. An effective synthetic perspective to spirooxindoles is the use of transition metals as the catalyst. This review discusses the synthesis of spirooxindoles catalyzed by transition metals and covers literature up to 2020.

Hypervalent Iodine Reagents in Palladium-Catalyzed Oxidative Cross-Coupling Reactions

Hypervalent iodine compounds are valuable and versatile reagents in synthetic organic chemistry, generating a diverse array of useful organic molecules. Owing to their non-toxic and environmentally friendly features, these reagents find potential applications in various oxidative functionalization reactions. In recent years, the use of hypervalent iodine reagents in palladium-catalyzed transformations has been widely studied as they are strong electrophiles and powerful oxidizing agents. For instance, extensive work has been carried out in the field of C–H bond functionalization via Pd-catalysis using hypervalent iodine reagents as oxidants. In addition, nowadays, iodine(III) reagents have been frequently employed as arylating agents in Pd-catalyzed C–H arylation or Heck-type cross-coupling reactions. In this review, recent advancements in the area of palladium-catalyzed oxidative cross-coupling reactions using hypervalent iodine reagents are summarized in detail.

Palladium-catalysed Heck-type alkenylation reactions in the synthesis of quinolines. Mechanistic insights and recent applications

Recent developments in Pd(0)- and Pd(ii)-catalysed alkenylation reactions for the synthesis of quinolines focusing on mechanistic understanding.

Application of isatin-derived saturated esters in the synthesis of 3,3'-spirooxindole γ-butyrolactams

Stable while reactive isatin-derived saturated esters have been utilized as 3-carbon synthons in a base-promoted formal [3 + 2] annulation with N-Boc imines. The developed protocol offers a direct pathway for the rapid and divergent construction of two classes of 3,3'-spirooxindole γ-butyrolactam skeletons that are recognized as the privileged structures of various bioactive compounds. This protocol also has the advantages of mild reaction conditions, scalability and wide reaction scope.

Palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones: synthesis of alkene-functionalized oxindoles

An efficient approach for the construction of alkene-functionalized oxindoles was developed via palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones.

Synthesis of difluoromethylated 2-oxindoles and quinoline-2,4-diones via visible light-induced tandem radical cyclization of N-arylacrylamides

Visible light-induced difluoromethylation of N-arylacrylamides to afford difluoromethylated 2-oxindoles and quinoline-2,4-diones with difluoromethyl 2-pyridyl sulfones as radical precursors has been disclosed.

Enantioselective palladium-catalyzed diarylation of unactivated alkenes

Enantioselective Pd-catalyzed diarylation of unactivated alkenes between arenediazonium salts and arylboronic acids has been developed. This method provides an efficient route to dihydrobenzofurans with all-carbon quaternary centers in good yields with 88–99% ee.

Ppm Cu Catalyst Enables tert-Alkylation Followed by C-H Cyclization To Synthesize Substituted Oxindoles

In this paper, we established highly efficient Cu-catalyzed tandem tert-alkylation C-H cyclization of α-bromocarbonyls and methacrylamides to produce substituted oxindoles. The maximum turnover number was up to 48 000 with reasonable yield. Although the catalyst loadings were very low, the reaction was not involving radical chain reaction. The resulting oxindoles were able to transform into aza-multicyclic compound via a reduction.

Transition-Metal-Free Synthesis of N-Hydroxy Oxindoles by an Aza-Nazarov-Type Reaction Involving Azaoxyallyl Cations

A novel transition-metal-free method to construct N-hydroxy oxindoles by an aza-Nazarov-type reaction involving azaoxyallyl cation intermediates is described. A variety of functional groups were tolerated under the weak basic reaction conditions and at room temperature. A one-pot process was also developed to make the reaction even more practical. This method provides alternative access to oxindoles and their biologically active derivatives.

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

Hypervalent iodine reagents have been developed as highly valuable reagents in synthetic organic chemistry during the past few decades. These reagents have been identified as key replacements of various toxic heavy metals in organic synthesis. Various synthetically and biologically important scaffolds have been developed using hypervalent iodine reagents either in stoichiometric or catalytic amounts. In addition, hypervalent iodine reagents have been employed for the synthesis of spirocyclic scaffolds via dearomatization processes. In this review, various approaches for the synthesis of spirocyclic scaffolds using hypervalent iodine reagents are covered including their stereoselective synthesis. Additionally, the applications of these reagents in natural product synthesis are also covered.

Highly Diastereoselective Palladium-Catalyzed Oxidative Carbocyclization of Enallenes Assisted by a Weakly Coordinating Hydroxyl Group

A highly diastereoselective palladium-catalyzed oxidative carbocyclization-borylation of enallenes assisted by a weakly coordinating hydroxyl group was developed. The reaction afforded functionalized cyclohexenol derivatives, in which the 1,3-relative stereochemistry is controlled (d.r. > 50:1). Other weakly coordinating oxygen-containing groups (ketone, alkoxide, acetate) also assisted the carbocyclization toward cyclohexenes. The reaction proceeds via a ligand exchange on Pd of the weakly coordinating group with a distant olefin group. The high diastereoselectivity of the hydroxyl-directed reaction could be rationalized by a face-selective coordination of the distant olefin. It was demonstrated that the primary coordination of the close-by oxygen-containing functionality was necessary for the reaction to occur and removal of this functionality shut down the reaction.

A tethering directing group strategy for ruthenium-catalyzed intramolecular alkene hydroarylation

We report a new catalyst design for N-heterocycle synthesis that utilizes an alkene-tethered amide moiety as a directing group for aromatic C-H activation. This tethering directing group strategy is demonstrated in a ruthenium-catalyzed intramolecular alkene hydroarylation with N-aryl acrylamides to form oxindole products.

Nickel-Catalyzed Domino Heck Cyclization/Suzuki Coupling for the Synthesis of 3,3-Disubstituted Oxindoles

The first nickel-catalyzed domino Heck cyclization/Suzuki coupling reaction for the synthesis of 3,3-disubstituted oxindoles bearing quaternary all-carbon centers is reported. A wide range of electrophiles, such as aryl iodides, bromides, triflates, and chlorides, are all compatible with the reaction conditions. Moreover, cheap aryl esters, which undergo catalytic C-O bond cleavage, could also be employed as electrophiles. The approach shows good yields and broad scope, complementing a more practical and sustainable alternative to the conventional palladium-based analogues.

NHC-catalyzed [4+2] cycloaddition reactions for the synthesis of 3′-spirocyclic oxindoles via a C–F bond cleavage protocol

A chiral NHC-catalyzed cycloaddition of γ-fluoroenals is developed. The nucleophilic γ-carbon generated via C–F bond cleavage undergoes highly enantioselective cycloaddition (up to >99% ee) to isatins and provides 3′-spirocyclic oxindoles in good yields (up to 91%).

Selective Palladium-Catalyzed Allenic C-H Bond Oxidation for the Synthesis of [3]Dendralenes

A highly selective palladium-catalyzed allenic C-H bond oxidation was developed, and it provides a novel and straightforward synthesis of [3]dendralene derivatives. A variety of [3]dendralenes with diverse substitution patterns are accessible with good efficiency and high stereoselectivity. The reaction tolerates a broad substrate scope containing various functional groups on the allene moiety, including ketone, aldehyde, ester, and phenyl groups. Also, a wide range of olefins with both electron-donating and electron-withdrawing aryls, acrylate, sulfone, and phosphonate groups are tolerated.

Pd-Catalyzed Intramolecular Aminoalkylation of Unactivated Alkenes: Access to Diverse N-Heterocycles

A highly efficient palladium-catalyzed intramolecular aminoalkylation of unactivated alkenes in the absence of an external ligand and oxidant is described. New C-N and C(sp³)-C(sp³) bonds are formed simultaneously. This general transformation allows for construction of diverse N-heterocycles. Mechanistic studies show that the process may involve a four-membered Pd(alkyl)amido intermediate.

Visible-light-induced and iron-catalyzed methylation of N-arylacrylamides with dimethyl sulphoxide: a convenient access to 3-ethyl-3-methyl oxindoles

An efficient synthesis of 3-ethyl-3-methyl oxindoles by visible-light promoted and iron-catalyzed difunctionalization of N-arylacrylamides with dimethyl sulphoxide was developed.

Cu-catalyzed intermolecular oxyalkylation of styrenes under air: access to diverse iminolactones

A practical, simple, and efficient copper-catalyzed oxyalkylation of styrenes with α-bromoacetamides for the synthesis of iminolactones was developed under air.

Oxidative bicyclization of N-tethered 1,7-enynes toward polycyclic 3,4-dihydroquinolin-2(1H)-ones via site-selective decarboxylative C(sp3)–H functionalization

A new Ag-catalyzed oxidative bicyclization of N-tethered 1,7-enynes with alkylcarboxylic acids for forming 41 examples of polycyclic 3,4-dihydroquinolin-2(1H)-ones has been established using readily accessible K₂S₂O₈ as an oxidant.

Palladium-catalyzed oxidative arylacetoxylation of alkenes: synthesis of indole and indoline derivatives

A method for the oxidative arylacetoxylation of alkenes has been developed to synthesize indole and indoline derivatives from readily accessible substrates.

Synthesis of Functionalized 6-Hydroxy-2-oxindole Derivatives by Phenoxide Cyclization

An apparent intramolecular cross-dehydrogenative coupling of N-(3-hydroxy)monoanilide of maleic esters comprising base promoted phenoxide cyclization and subsequent base-mediated aerobic oxidation was developed to synthesize a variety of 2-(6-hydroxy-2-oxoindolin-3-ylidene)acetate derivatives. The isolation of intermediate cyclized products during the large scale reactions and their ready dehydrogenation with 1 equiv of base support this proposed two-step path.