Pd-Catalyzed Cascade Cyclization/Thiocarbonylation with Thioformates: Synthesis of Thioester-Functionalized Oxindoles.

A Pd-catalyzed thiocarbonylative cyclization of N-(o-iodoaryl)acrylamides with easily accessible thioformates has been developed. The reaction has a wide substrate scope with good yields and represents a powerful route to the synthesis of thioester-functionalized oxindoles. Both S-aryl and alkyl thioformates as the thioester sources were well tolerated. The active Pd-CO intermediate may play an important role in the transformation process.

Palladium-Catalyzed Allylation of P(O)H Compounds: Access to 2-Fluoroallylic Phosphorus Compounds.

An efficient palladium-catalyzed 2-fluoroallylation of P(O)H compounds with gem-difluorocyclopropanes is presented. The reaction provides a variety of 2-fluoroallylic phosphorus compounds in good yields with high Z selectivity through the sequential C-C bond activation, C-F bond cleavage, and C-P coupling process. Various H-phosphonates, H-phosphinates, and secondary phosphine oxides are all tolerated. In addition, the gram-scale synthesis and the late-stage modification of complex bioactive molecules show practical utilities of the transformation.

Palladium-Catalyzed Heck Cyclization with P(O)H Compounds to Construct Phosphinonyl-Azaindoline and -Azaoxindole Derivatives.

We report herein a concise method for the construction of phosphinonyl-azaindoline and -azaoxindole derivatives via a palladium-catalyzed cascade cyclization with P(O)H compounds. Various H-phosphonates, H-phosphinates, and aromatic secondary phosphine oxides are all tolerated under the reaction conditions. Furthermore, the phosphinonyl-azaindoline isomer families such as 7-, 5-, and 4-azaindolines could be synthesized in moderate to good yields.

Highly regioselective and stereoselective cascade reductive cyclization of δ-ketoamide: practical access to oxa-bridged benzazepines.

A highly regioselective and stereoselective cascade reduction cyclization of δ-ketoamide is realized under LiAlH4-assisted conditions, providing an atom-economical and straightforward approach to access oxa-bridged benzazepines in moderate to good yields. This method overcomes the limitations of aldehydes or other precursors of primary alcohols and realizes the cascade reduction cyclization of secondary alcohol anions generated in situ from ketones. The reaction proceeds with broad substrate scope and good functional group compatibility.

Palladium-Catalyzed Cyclization Coupling with Cyclobutanone-Derived N-Tosylhydrazones: Synthesis of Benzofuran-3-Cyclobutylidenes and Spirocyclobutanes.

A palladium-catalyzed cyclization coupling of iodoarene-tethered alkynes with cyclobutanone-derived N-tosylhydrazones is reported, providing a convenient and efficient approach to benzofuran-3-cyclobutylidenes. On this basis, spirocyclobutanes can be generated smoothly in an efficient cascade manner by the addition of dienophiles. Good yields and scalability are demonstrated. Sequential intramolecular carbopalladation, palladium-carbene migratory insertion, δ-hydride elimination, and cycloaddition processes are involved.

Palladium-catalyzed Heck cyclization/carbonylation with formates: synthesis of azaindoline-3-acetates and furoazaindolines.

We report herein a palladium-catalyzed domino cyclization/carbonylation to access ester-functionalized azaindolines, applying formates as a convenient carbonyl source. All four azaindoline isomers were constructed, exhibiting good functional group compatibility. On this basis, modifying the starting tether on the aminopyridine led to furoazaindolines via an intramolecular reductive cyclization after the palladium-catalyzed process.

Palladium-Catalyzed Sequential Vinyl C-H Activation/Dual Decarboxylation: Regioselective Synthesis of Phenanthrenes and Cyclohepta[1,2,3-de]naphthalenes.

The application of a C(vinyl), C(aryl)-palladacycle from vinyl-containing substrates is challenging due to the interference of a reactive double bond in palladium catalysis. This Letter describes a [4 + 2] or [4 + 3] cyclization based on a C(vinyl), C(aryl)-palladacycle by employing α-oxocarboxylic acids as the insertion units under a palladium/air system. The reaction proceeded through the key vinyl C-H activation and dual decarboxylation sequence, forming phenanthrenes and cyclohepta[1,2,3-de]naphthalenes regioselectively in good yields. The synthetic versatility of this protocol is highlighted by the gram-scale synthesis and synthesizing functional material molecule.

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.

Palladium-Catalyzed Cascade Cyclization/Dearomatization/Arylation of Alkyne-Containing Phenol-Based Biaryls with Aryl Halides: An Entry to Diversely Functionalized Spirocyclohexadienones.

A convenient method for the synthesis of aryl-functionalized spirocyclohexadienone scaffolds from alkyne-containing phenol-based biaryls with aryl halides via palladium-catalyzed cyclization/dearomatization/arylation is developed. The approach provides a series of spirocyclohexadienone molecules in moderate to high yields. The reaction occurs chemoselectively through dearomative C-arylation rather than common O-arylation of phenols.

Base-promoted direct synthesis of functionalized N-arylindoles via the cascade reactions of allenic ketones with indoles.

A convenient Cs2CO3-promoted cascade benzannulation reaction of allenic ketones with indoles was achieved for the synthesis of functionalized N-arylindole derivatives under transition-metal-free conditions. A series of readily available starting materials can undergo the process successfully. It represents a practical method for the construction of N-arylindole scaffolds with high atom economy.

Palladium-Catalyzed Cascade Carbopalladation/Phenol Dearomatization Reaction: Construction of Diversely Functionalized Spirocarbocyclic Scaffolds.

A novel palladium-catalyzed cascade carbopalladation/phenol dearomatization reaction has been achieved. The process provides a variety of indolone-, dihydrobenzofuran-, dihydrobenzopyran- and hydroquinoline-containing spirofused molecules bearing two quaternary centers in moderate to good yields. The potential synthetic utility of this method is demonstrated by a gram-scale experiment and further transformations.

Palladium-Catalyzed Domino Cyclization/Alkylation of Terminal Alkynes: Synthesis of Alkynyl-Functionalized Azaindoline Derivatives.

A novel palladium-catalyzed domino cyclization/alkylation of terminal alkynes was achieved for the synthesis of alkynyl-functionalized 3,3-disubstituted azaindoline derivatives under air atmosphere conditions. Various types of terminal alkynes, including aromatic alkynes, aliphatic alkynes, and ferrocene acetylene, can undergo the process successfully. The protocol provides a range of alkynyl-functionalized azaindoline scaffolds bearing a quarternary carbon center.

Synthesis of polyfluoroarene-substituted benzofuran derivatives via cooperative Pd/Cu catalysis.

A cooperative Pd/Cu-catalyzed dual C-H bond activation of electron-deficient polyfluoroarenes with aryl halides is developed. This protocol provides a unique and strategically distinct access to a variety of polyfluoroarene-substituted benzofuran derivatives. This is the first example of the introduction of electron-deficient arenes to a Catellani-type reaction.

CuCl-Catalyzed direct C-H alkenylation of benzoxazoles with allyl halides.

An efficient and concise CuCl-catalyzed C2-alkenylation reaction of benzoxazoles with allyl halides has been established. The distinctive features of this protocol include the use of an inexpensive copper salt as a catalyst, simple and readily available starting materials, and ligand-free conditions. An important application of this method to the synthesis of 1,3-diene substituted benzoxazoles has also been achieved.

Palladium-Catalyzed Intramolecular Dearomatization of Indoles via Decarboxylative Alkynyl Termination.

A highly diastereoselective dearomatization of indoles via palladium-catalyzed decarboxylative alkynyl termination was developed. This protocol provides dissimilar tetracyclic and tetrasubstituted indoline scaffolds bearing congested stereocenters, which led to operationally simple conditions, short time, and broad substrate scope. Additionally, this reaction system could be scaled to gram quantities in a satisfactory yield and diastereoselectivity.

Palladium-Catalyzed Domino Heck/Intermolecular C-H Bond Functionalization: Efficient Synthesis of Alkylated Polyfluoroarene Derivatives.

An efficient palladium-catalyzed alkylation of electron-deficient polyfluoroarenes is described. The protocol provides a useful and operationally simple access to a broad scope of alkylated polyfluoroarene derivatives in moderate to excellent yields. This also represents the first example of the introduction of a polyfluoroarene structure involving an alkylpalladium(II) intermediate.

Silver-Catalyzed Oxidative Cyclization of Propargylamide-Substituted Indoles: Synthesis of Phosphorated Indoloazepinones Derivatives.

A silver-catalyzed oxidative cyclization of 2- or 3-propargylamide-substituted indoles to synthesize phosphorated indoloazepinone derivatives is described. This reaction displays a difunctionalizalion of alkynes with diphenylphosphine oxides to construct a seven-membered ring through a radical cyclization process. The indoloazepinones derivatives are common structural motifs found in many natural products and pharmaceuticals.

Palladium-catalyzed dearomative cyclization by a norbornene-mediated sequence: a route to spiroindolenine derivatives.

The first palladium-catalyzed dearomative cyclization via a modified Catellani-type C-H functionalization has been realized. The new strategy led to a series of spiroindolenine derivatives bearing an all-carbon quaternary spirocenter from simple aryl halides and substituted indoles.

Lewis Acid Mediated Tandem Reaction of Propargylic Alcohols with Hydroxylamine Hydrochloride To Give α,ß-Unsaturated Amides and Alkenyl Nitriles.

We have developed a highly selective method for the synthesis of α,ß-unsaturated amides and alkenyl nitriles from readily available propargylic alcohols. The reaction proceeded smoothly under the neutral conditions with hydroxylamine hydrochloride (NH2OH·HCl) as the nitrogen source. The development of these new strategies has significantly extended the application of hydroxylamine hydrochloride to the chemistry of propargylic alcohols. Moreover, both secondary and tertiary alcohols have been highly regioselectively transformed to the desired products with good functional group compatibility.

Palladium-Catalyzed Radical Cascade Iododifluoromethylation/Cyclization of 1,6-Enynes with Ethyl Difluoroiodoacetate.

A novel and convenient Pd-catalyzed radical cascade iododifluoromethylation/cyclization of 1,6-enynes with ethyl difluoroiodoacetate is demonstrated. The proposed transformation presents high stereoselectivity under mild and facile reaction conditions, thereby allowing an efficient access to a variety of iodine-containing difluoromethylated pyrrolidines. A possible radical pathway for the transformation is proposed on the basis of the results of control experiments and relevant literature reviews.