Domino Carbopalladation/CH Functionalization Sequence: An Expedient Synthesis of Bis-Heteroaryls through Transient Alkyl/Vinyl-Palladium Species Capture

Pd-catalyzed 5-exo-dig cyclization/etherification cascade of N-propargyl arylamines for the synthesis of polysubstituted furans

A method for the synthesis of furans bearing indoline skeletons was developed via an intramolecular palladium-catalyzed 5-exo-dig cyclization/etherification cascade of N-propargyl arylamines containing a 1,3-dicarbonyl side chain. This method realized the first capture of vinyl carbopalladiums by ketones as O-nucleophiles and showed a wide range of substrate tolerability affording trisubstituted furans in various yields. The enantioselective version for this domino process and diverse derivatizations of the reaction products were also studied.

Palladium/XuPhos-catalyzed enantioselective cascade Heck/intermolecular C(sp2)-H alkylation reaction

Palladium-catalyzed enantioselective domino Heck/intramolecular C-H functionalization reaction, as a valuable strategy for creating molecular diversity, has remained a prominent challenge. Here, we describe a Pd/XuPhos catalyst for asymmetric domino Heck/intermolecular C-H alkylation of unactivated alkenes with diverse polyfluoro- and heteroarenes in a highly chemo- and enantioselective manner. This process enables efficient synthesis of various dihydrobenzofurans, indolines and indanes, which are of interest in pharmaceutical research and other areas. Late-stage modifications of the core structures of natural products are also well showcased. Moreover, synthetic transformations create a valuable platform for preparing a series of functionalized molecules. Several control experiments for mechanistic study are conducted to pursue a further understanding of the reaction.

Pd-Catalyzed Vicinal Intermolecular Annulations of Iodoarenes, Indoles, and Carbazoles with Enynes

Reaching the formidable C-H corners has been one of the top priorities of organic chemists in the recent past. This prompted us to disclose herein a vicinal annulation of 2-iodo benzoates, indoles, and carbazoles with N-embedded 1,6-enynes through 7-/8-membered palladacycles. The relay does not require the assistance of any directing group, leading to multicyclic scaffolds, which are readily diversified to an array of adducts (with new functional tethers and/or three contiguous stereocenters), in which we showcase a rare benzylic mono-oxygenation.

Palladium-catalyzed Heck-carbonylation of alkene-tethered carbamoyl chlorides with aryl formates

We report a palladium-catalyzed Heck-carbonylation of alkene-tethered carbamoyl chlorides by utilizing aryl formates as convenient CO surrogates. One C-O and two C-C bonds are constructed to give diversiform esterified oxindoles/γ-lactams bearing an all-carbon quaternary stereocenter under gas-free conditions. This transformation features a wide substrate scope and good functional group tolerance and can be easily applied to late-stage functionalization.

N-(2-Arylethyl)-2-methylprop-2-enamides as Versatile Reagents for Synthesis of Molecularly Imprinted Polymers

The paper describes the formation of six aromatic N-(2-arylethyl)-2-methylprop-2-enamides with various substituents in benzene ring, viz., 4-F, 4-Cl, 2,4-Cl₂, 4-Br, 4-OMe, and 3,4-(OMe)₂ from 2-arylethylamines and methacryloyl chloride in ethylene dichloride with high yields (46–94%). The structure of the compounds was confirmed by ¹H NMR, ¹³C NMR, IR, and HR-MS. Those compounds were obtained to serve as functionalized templates for the fabrication of molecularly imprinted polymers followed by the hydrolysis of an amide linkage. In an exemplary experiment, the imprinted polymer was produced from N-(2-(4-bromophenyl)ethyl)-2-methylprop-2-enamide and divinylbenzene, acting as cross-linker. The hydrolysis of 2-(4-bromophenyl)ethyl residue proceeded and the characterization of material including SEM, EDS, ¹³C CP MAS NMR, and BET on various steps of preparation was carried out. The adsorption studies proved that there was a high affinity towards the target biomolecules tyramine and L-norepinephrine, with imprinting factors equal to 2.47 and 2.50, respectively, when compared to non-imprinted polymer synthesized from methacrylic acid and divinylbenzene only.

Palladium-catalyzed cross-coupling of unreactive C(sp3)-H bonds with azole C(sp2)-H bonds by using bromide as a traceless directing group

A palladium-catalyzed intermolecular cross-coupling of unreactive C(sp³)-H bonds and azole C(sp²)-H bonds with bromide as a traceless directing group is described. The judicious selection of the bulky and electron-rich phosphine ligand is the key for the success of this cascade process. The protocol features a broad substrate scope, excellent regioselectivity, and good functional group tolerance.

Palladium-catalyzed cyclizative cross coupling of ynone oximes with 2-haloaryl N-acrylamides for isoxazolyl indoline bis-heterocycles

Metal-catalyzed cyclizative cross-coupling reactions have attracted enormous attention due to their unique cascade nature. We demonstrated, herein, a dual-cyclizative coupling of ynone oxime ethers with acrylamides for the synthesis of methylene-linked isoxazolyl 2-oxindoles. The cascade was triggered by a palladium(II)-catalyzed ynone oxime ether cyclization, which underwent a Heck-type coupling intercepted by an aryl iodide insertion. Control experiments were carried out to understand the mechanism.

Metal-catalyzed asymmetric heteroarylation of alkenes: diverse activation mechanisms

This review summarizes the state-of-the-art in transition metal-catalyzed asymmetric alkylation of heteroarenes using alkenes (covering literature from 2000 to late 2021). Based on elementary reactions on metals for substrate activation, these reactions are broadly classified in several categories: (A) concerted oxidative addition of heteroaryl C-H bonds on rhodium(I) and iridium(I), (B) ligand-to-ligand hydrogen transfer (LLHT) on low-valent 3d metal complexes of nickel and cobalt, (C) different ways for deprotonation of heteroaryl C-H bonds by late transition metal complexes, especially palladium, including electrophilic aromatic substitution and a related mechanism, base-assisted intramolecular electrophilic substitution, concerted and nonconcerted metalation deprotonation, (D) σ-bond metathesis by d⁰ early transition metal complexes, (E) electrophilic activation of olefins by Pd(II), Pt(II) and Au(I), and (F) metal hydride insertion of aryl olefins and dienes. The demand to achieve enantiocontrol in the heteroarylation reactions has also driven innovation in chiral ancillary ligands, exemplified by extremely bulky, chiral N-heterocyclic carbenes for nickel catalysts, bulky monodentate oxazolines for Wacker-type reactions and chiral cyclopentadienyl ligands for half-sandwich complexes of scandium.

Accessing Unsymmetrically Linked Heterocycles through Stereoselective Palladium-Catalyzed Domino Cyclization

A palladium-catalyzed strategy is presented to synthesize unsymmetrically linked heterocycles within stereoselective tetrasubstituted olefins. This reaction is proposed to occur via a vinyl-Pd^II intermediate capable of initiating the cyclization of various alkyne-tethered nucleophiles. Products are formed in up to 96 % yield and excellent stereoselectivities are obtained using low catalyst loadings. This transformation was scalable up to 1 mmol and mechanistic studies suggest a syn-carbopalladation of the carbamoyl chloride followed by Pd^II -catalyzed cyclization of alkyne-tethered nucleophiles.

Pd-Catalyzed alkynyl aryl iodide cyclization/alkylation with cyclobutanols

A palladium-catalyzed cis-selective carboalkylation of internal alkynes with cyclobutanols is reported, providing a useful and facile approach to alkyl-substituted olefins with moderate to good yields and excellent stereoselectivity.

Palladium-Catalyzed Difunctionalization of Alkenes by Relay Coupling with Propargylic Pyridines: Synthesis of Indolizine and Indolizinone-Containing Bisheterocycles

Palladium-catalyzed arylation/heteroarylation of aryl halide-tethered alkenes with propargylic pyridines has been established, which provides direct and efficient access to various oxindole, azaoxindole, dihydrobenzopyran, indole, and benzofuran-linked indolizines in good yields with a broad substrate scope and high functional group tolerance. This process enables the formation of one C-N and two C-C bonds in a single operation through an intramolecular carbopalladation and cycloisomerization sequence. Furthermore, an indolizinone-linked bisheterocyclic framework containing indole and benzofuran could be synthesized conveniently from tertiary propargylic alcohols involving methyl or phenyl migration.

Palladium-Catalyzed Aryl-Furanylation of Alkenes: Synthesis of Benzofuran-Containing 3,3-Disubstituted Oxindoles

A novel palladium-catalyzed aryl-furanylation of alkenes is described. This protocol provided a straightforward route to the synthesis of various benzofuran-containing 3,3-disubstitutedoxindole derivatives bearing a quarternary carbon center. In the cascade process, one C(sp²)-O bond, two C(sp²)-C(sp³) bonds, an oxindole, and a furan ring are formed in a single chemical operation.

Domino Heck/Hiyama cross-coupling: trapping of the σ-alkylpalladium intermediate with arylsilanes

A palladium-catalyzed domino Heck cyclization/Hiyama coupling reaction by the trapping of the σ-alkylpalladium intermediate with arylsilanes is described. A wide range of aryl-tethered alkenes and arylsilanes are all compatible with the reaction conditions. This approach shows good yields and excellent functional group tolerance, presenting a more practical and sustainable alternative to the conventional domino Heck cyclization/Suzuki coupling reaction.

Dicarbofunctionalization of unactivated alkenes by palladium-catalyzed domino Heck/intermolecular direct hetero arylation with heteroarenes

A palladium-catalyzed domino Heck/intermolecular direct hetero arylation sequence of unactivated alkenes was developed, providing 1,2,3-triazole containing bisheterocycles bearing all-carbon quaternary centers with yields of 25-90%. The protocol was extended to 1,3,4-oxadiazoles as well. The installed triazole was further exploited for late-stage functionalizations, and the mechanistic studies indicate the involvement of C-H activation.

Palladium-Catalyzed Arylation/Heteroarylation of Indoles: Access to 2,3-Functionalized Indolines

A palladium-catalyzed diastereoselective dearomatization of N-(2-bromobenzoyl)indoles by an arylation/heteroarylation sequence is reported. Diverse functionalized indolines are accessed in good to excellent yields and selectivity. Studies conducted on the effects of copper in the reaction revealed that, along with improving conversions, the additive inhibits epimerization of the product.

Domino carbometalation/coupling reactions of N-arylpropiolamides: a novel and promising synthetic strategy toward stereocontrolled preparation of highly substituted 3-methyleneindolinones

3-Methyleneindolinone derivatives are important structural motifs found in many compounds of natural occurrence and pharmacological significance.