Regioselective Pd-Catalyzed Carbopalladation/Decarboxylative Allylic Alkynylation of ortho-Iodoallenamides with Alkynyl Carboxylic Acids

Synthesis of Indole- and Benzofuran-Based Benzylic Sulfones by Palladium-Catalyzed Sulfonylation of ortho-Iodoaryl Allenes

A highly efficient palladium-catalyzed domino coupling reaction of ortho-iodoaryl allene with sodium sulfonates under mild conditions is described. This novel method provides a practical protocol to access diverse indole- and benzofuran-containing sulfones by simultaneous construction of C(sp2)-C(sp2) bond and a C(sp3)-S bonds in one pot. The salient features of this transformation include simple operations, broad substrate scope, and good functional group tolerance.

TCCA/RSeSeR-Mediated Selenoalkoxy of Allenamides via a Radical Process: Synthesis of Selanyl-allylic N,O-Aminals

An efficient TCCA (trichloroisocyanuric acid)/RSeSeR-mediated selenoalkoxy of allenamides for the construction of selanyl-allylic N,OA-aminal derivatives was developed. The reaction exhibits good functional group tolerance and high efficiency, affording the products in good to excellent yields. Mechanistic investigations indicated that a selanyl-allylic radical intermediate was first formed via the RSe radical added to the central carbon of allenamides, which subsequently furnished highly stable selanyl-allylic carbocation intermediate by abstraction of an electron by the chlorine radical. Moreover, this is the first report of using selenium reagent (RSeCl) to activate allenamides via a radical process.

Dual Nickel/Photoredox-Catalyzed Arylsulfonylation of Allenes

The nickel/photoredox dual catalysis system is an efficient conversion platform for the difunctionalization of unsaturated hydrocarbons. Herein, we disclose the first dual nickel/photoredox-catalyzed intramolecular 1,2-arylsulfonylation of allenes, which can accurately construct a C(sp2)-C(sp2) bond and a C(sp3)-S bond. The reaction exhibits excellent chemoselectivity and regioselectivity, allowing modular conformations of a diverse series of 3-sulfonylmethylbenzofuran derivatives. Control experiments showed that the bipyridine ligand is crucial for the formation of a stable σ-alkyl nickel intermediate, providing the possibility for sulfonyl radical insertion. Meanwhile, the electrophilic sulfonyl radical facilitates further oxidative addition of the σ-alkyl nickel intermediate and inhibits addition with allenes. In addition, control experiments, cyclic voltammetry tests, Stern-Volmer experiments, and density functional theory calculations afford evidence for the Ni(0)/Ni(I)/Ni(II)/Ni(III) pathway in this 1,2-arylsulfonylation.

Synthesis of Substituted 1,2-Dihydroisoquinolines by Palladium-Catalyzed Cascade Cyclization-Coupling of Trisubstituted Allenamides with Arylboronic Acids

1,2-Dihydroisoquinolines are important compounds due to their biological and medicinal activities, and numerous approaches to their synthesis have been reported. Recently, we reported a facile synthesis of trisubstituted allenamides via N-acetylation followed by DBU-promoted isomerization, where various substituted allenamides were conveniently synthesized from readily available propargylamines with high efficiency. In light of this research background, we focused on the utility of this methodology for the synthesis of substituted 1,2-dihydroisoquinolines. In this study, a palladium-catalyzed cascade cyclization-coupling of trisubstituted allenamides containing a bromoaryl moiety with arylboronic acids is described. When N-acetyl diphenyl-substituted trisubstituted allenamide and phenylboronic acid were treated with 10 mol% of Pd(OAc)2, 20 mol% of P(o-tolyl)3, and 5 equivalents of NaOH in dioxane/H2O (4/1) at 80 °C, the reaction proceeded to afford a substituted 1,2-dihydroisoquinoline. The reaction proceeded via intramolecular cyclization, followed by transmetallation with the arylboronic acid of the resulting allylpalladium intermediate. A variety of highly substituted 1,2-dihydroisoquinolines were concisely obtained using this methodology because the allenamides, as reaction substrates, were prepared from readily available propargylamines in one step.

Palladium-catalysed aryl/monofluoroalkylation of allenamides: access to fluoroalkyl indoles and isoquinolones

A palladium catalysed construction of fluoroalkyl indoles and isoquinolones through aryl/monofluoroalkylation of allenamides has been developed. Monofluoromethyl-substituted heterocycles could be accessed under mild conditions with broad functional group tolerance. In addition, indole-oxindole bisheterocyclic scaffolds bearing a fluorine atom were successfully synthesized with 3-fluoro-oxindole as the nucleophile by applying this method.

Regiodivergent cascade cyclization/alkoxylation of allenamides via N-protecting group driven rearrangement to access indole and indoline derivatives

A mild, palladium-catalyzed domino Heck-cyclization/alkoxylation sequence of aryl halide tethered allenamides is described, providing regiodivergent indole and indoline derivatives controlled by the N-protecting group. This room temperature reaction provided a functionalizable olefinic moiety with broad substrate scope. Preliminary mechanistic studies support the rearrangement of an indoline-derived intermediate to indoles with the N-acetyl allenamides forming free (NH) indoles.

Synthesis of 1,2-diselenides via potassium persulfate-mediated diselenation of allenamides with diselenides

An efficient potassium persulfate-mediated radical addition of allenamides with diselenides was developed to create a workable route to 1,2-diselenide products. The reaction tolerates a wide spectrum of functional groups to deliver the products in good to excellent yields. Mechanistic investigations including a calculation study indicated that the radical cascade proceeds through a vinyl radical intermediate, which is formed via a selenium radical added to the terminal CC double bond of allenamides.

Copper-Mediated Cyclization of o-Hydroxyaryl Enaminones with 3-Indoleacetic Acids toward the Synthesis of 3-Indolmethyl-Chromones

Here, we describe a copper-mediated tandem decarboxylative coupling/annulation protocol of o-hydroxyaryl enaminones with 3-indoleacetic acids. A series of 3-indolmethyl-chromones were afforded in up to 97% yield. A one-pot method for 3-indolmethyl-chromones from o-hydroxy acetophenones, N, N-dimethylformamide dimethyl acetal, and 3-indoleacetic acids was also developed. Derivatization of the products was conducted to provide various indolmethyl-substituted pyrimidines. Moreover, a biological evaluation revealed that some compounds had anti-influenza viral activities.

Synthesis of dihydroisoquinolinone-4-methylboronic esters via domino Heck/borylation using a structurally characterized palladacycle as a catalyst

Synthesis of dihydroisoquinolinone-4-methylboronic esters from N-allylcarboxamides and B₂(Pin)₂via domino Heck/borylation approach is reported. A quinoxaline-based NHC-palladacycle [Pd(C∧C:)PPh₃Cl], which has been structurally characterized, is used as a catalyst. The scope of the substrate with a wide range of substituents is explored. In addition to the synthesis of title compounds, a few examples of methylboronic esters of indoline and benzofuran motifs have also been prepared using the same protocol.

Synthesis of dihydroisoquinolinone-4-methylboronic esters from N-allylcarboxamides and B₂(Pin)₂via domino Heck/borylation has been achieved by using a quinoxaline-based NHC-palladacycle [Pd(C∧C:)PPh₃Cl].

Copper-Mediated Decarboxylative Coupling of 3-Indoleacetic Acids with Pyrazolones

A copper-mediated decarboxylative coupling reaction of 3-indoleacetic acids with pyrazolones was described. This protocol realized new functionalization of pyrazolones under simple reaction conditions and exhibited high functional group compatibility and broad substrate scope. Notably, the products displayed antiproliferative activity against cancer cells.

An organophotoredox-catalyzed redox-neutral cascade involving N-(acyloxy)phthalimides and allenamides: synthesis of indoles

An organophotoredox-catalyzed radical cascade of allenamides and alkyl N-(acyloxy)phthalimides for the synthesis of indoles is documented. The method features mild and robust reaction conditions, and exhibits broad scope. The tandem process enriches the limited repertoire of alkyl NHPI ester addition on electron-rich π-bonds as well as radical chemistry involving allenamides.

Palladium-Catalyzed Allenamide Carbopalladation/Allylation with Active Methine Compounds

A palladium-catalyzed allenamide carbopalladation/allylation with active methine compounds has been developed. Various indoles and isoquinolinones bearing a quaternary carbon center were achieved with good efficiency, a broad substrate scope and good functional group tolerance. This reaction underwent cascade oxidative addition, carbopalladation, and allylic alkylation, and two new C-C bonds were formed in one pot.

Pd-Catalyzed Domino Reactions Involving Alkenes To Access Substituted Indole Derivatives

Palladium-catalyzed domino reactions are advanced tools in achieving various nitrogen-containing heterocycles in an efficient and economical manner due to the reduced number of steps in the process. This review highlights recent advances in domino processes aimed at the synthesis of indole derivatives and polycyclic systems containing the indole nucleus in intra/intra- or intra/intermolecular reactions. In particular, we consider domino processes that involve a double bond in a step of the sequence, which allow the issue of regioselectivity in the cyclization to be faced and overcome. The different sections in this review focus on the synthesis of the indole nucleus and functionalization of the scaffold starting from different substrates that have been identified as activated starting materials, which involve a halogenated moiety or unactivated unsaturated systems. In the former case, the reaction is under Pd(0) catalysis, and in the second case a Pd(II) catalytic species is required and then an oxidant is necessary to reconvert the Pd(0) into the active Pd(II) species. On the other hand, the second method has the advantage that it uses easy available and inexpensive substrates.

1 Introduction

2 Indole Scaffold Synthesis

2.1 Activated Substrates

2.2 Unactivated Substrates

3 Functionalization of Indole Scaffold

3.1 Activated Substrates

3.2 Unactivated Substrates

4 Conclusions