Palladium-Catalyzed Three-Component Cascade Carbonylation Reaction to Construct Benzofuran Derivatives.

A novel three-component cyclization carbonylation reaction of iodoarene-tethered propargyl ethers with amine and CO is reported. This palladium-catalyzed cascade reaction undergoes a sequence of oxidative addition, unsaturated bond migration, carbonyl insertion, and nucleophilic attack to deliver the benzofuran skeleton. Both aromatic amines and aliphatic amines could proceed smoothly in this transformation under one atm of CO.

Synthesis of 3(2H)-furanone derivatives: p-TsOH/halotrimethylsilane promoted cycloketonization of γ-hydroxyl ynones.

A p-TsOH/halotrimethylsilane facilitated cycloketonization of γ-hydroxyl ynones is detailed. This methodology enables the one-step synthesis of polysubstituted 3(2H)-furanone products. It is remarkable that the reaction exhibits excellent regio- and chemoselectivity by the addition of very small quantities of p-toluenesulfonic acid and water.

Regioselective C-H Active Carbonylation via 1,4-Palladium Migration.

We report a highly regioselective three-component coupling reaction of styrene, CO gas, and an amine compound to synthesize multisubstituted α,ß-unsaturated amides, which involves a palladium-catalyzed sequential 1,4-palladium migration, C(sp2)-H activation, carbonylation, and amination. Salient features of this strategy include the use of 1 atm of CO, excellent stereochemistry, and good functional group tolerance. Further, a series of control experiments and density functional theory calculations were performed to afford some insights for the transfer mechanism.

Redox Neutral Radical-Relay Nickel-Catalyzed Remote Carbonylation.

A novel and efficient method for the catalytic installation of a carbonyl group via remote radical coupling is disclosed. The nickel-catalyzed reaction proceeds to undergo a sequential single-electron transfer, 1,5-hydrogen atom transfer, and carbonyl insertion, thus providing the α-substituted ketone. Further, this reaction could be carried out smoothly under normal pressure and redox-neutral conditions, and demonstrated functional-group compatibility and excellent site-selectivity.

Nickel-Catalyzed Three-Component Tandem Radical Cyclization 1,5-Difunctionalization of 1,3-Enynes and Alkyl Bromide.

A nickel-catalyzed three-component tandem radical cyclization reaction of aryl bromides with 1,3-enynes and aryl boric acids to construct γ-lactam-substituted allene derivatives has been described. This protocol provides lactam alkyl radicals through the free radical cyclization process, which can be effectively used to participate in the subsequent multicomponent coupling reaction so that 1,3-enynes could directly convert into corresponding poly-substituted allene compounds. In addition, this efficient method enjoys a broad substrate scope and provides a series of 1,5-difunctionalized allenes in a one-pot reaction.

Access to Polysubstituted Halophosphorylated Dihydrofurans via Halotrimethylsilane-Promoted Cascade Cyclization of γ-Hydroxyl Ynones with Diphenylphosphine Oxides.

A halotrimethylsilane (TMSX) accelerated cascade halophosphorylation and cycloisomerization of γ-hydroxyl ynones with diphenylphosphine oxides is presented. This methodology allows the one-step synthesis of practical polysubstituted halophosphorylated dihydrofuran derivatives. It is noteworthy that halotrimethylsilane functions as a halogenation reagent as well as a promoter to initiate this transformation. In addition, the reaction system can also be scaled up to gram quantities, and the produced halogenated compounds can undergo further derivatizations by Pd-catalyzed coupling reactions.

Directed Copper-Catalyzed Tandem Radical Cyclization Reaction of Alkyl Bromides and Unactivated Olefins.

The free radical cyclization reaction is a promising strategy for ring framework formation. Herein, we report a copper-catalyzed tandem radical cyclization strategy for preparing substituted lactam derivatives. This reaction proceeds through a radical coupling approach, which not only allows a wide range of alkenes but also is quite compatible with the primary, secondary, and tertiary radicals. In addition, density functional theory calculations were performed to gain insights into the reaction mechanism.

Iron(II)-Catalyzed Bisphosphorylation Cascade Cycloisomerization of γ-Hydroxyl Ynones and Diphenylphosphine Oxides: Synthesis of Highly Substituted Bisphosphorylated Dihydrofuran Derivatives.

An iron(II)-catalyzed bisphosphorylation cascade cycloisomerization of readily accessible γ-hydroxyl ynones and diphenylphosphine oxides is described. This strategy provides a variety of valuable polysubstituted bisphosphorylated dihydrofuran scaffolds via the construction of two C-P bonds and one C-O bond within a single procedure. This developed reaction system demonstrates good functional group compatibilities with considerably low catalyst consumption (as low as 1%), which could be further scaled up to gram quantities in satisfactory yields.

Copper-Catalyzed Radical Aryl Migration Approach for the Preparation of Cyanoalkylsulfonylated Oxindoles/Cyanoalkyl Amides.

A copper-catalyzed radical cross-coupling of oxime esters and activated alkenes is accomplished for the synthesis of cyanoalkylsulfonylated oxindoles and cyanoalkyl amides via an aryl migration strategy. Specifically, the subsequent mechanism research indicates that the unique desulfonylation and sulfone addition processes were involved in the transformation. This transformation is identified as having good functional group applicability with two different quaternary stereocenter in a regioselective manner, which is controlled by the substituent group of the nitrogen.

Synthesis of C4-Substituted Indoles via a Catellani and C-N Bond Activation Strategy.

This paper describes the case of a cross study between the C-N bond cleavage reaction field and the Catellani-Lautens reaction system. A series of highly functionalized C4-substituted indoles were synthesized using this strategy. By screening the alkyl groups of amines, the energy barrier of C-N bond cleavage reaction was reduced and the corresponding allenization products were avoided. Finally, the density functional theory calculation shows that the inert C-N bond activation reaction is not a concerted process; on the contrary, the coupling reaction first generates indole quaternary ammonium salt, and then C-N bond cleavage occurs via an SN2 process.

Visible-Light-Induced Pd-Catalyzed Radical Strategy for Constructing C-Vinyl Glycosides.

A novel visible-light-induced palladium-catalyzed Heck reaction for bromine sugars and aryl olefins with high regio- and stereochemistry selectivity for the preparation of C-glycosyl styrene is described. This reaction takes place in one step at room temperature by using a simple and readily available starting material. This protocol can be scaled up to a wide range of glycosyl bromide donors and aryl olefin substrates. Mechanistic studies indicate that a radical addition pathway is involved.

Iodine promoted cascade cycloisomerization of 1-en-6,11-diynes.

An iodine promoted cascade cycloisomerization of 1-en-6,11-diynes is presented for the easy preparation of tetrahydrobenzo[f]isoquinolines. This developed reaction system is identified as having good functional-group applicability and can be scaled up to gram quantities. In this transformation, two new cyclic frameworks and one carbonyl group are formed with four new bonds constructed. Additionally, the resulting iodo-substituted compounds could be further derived through simple elimination reactions.

AgSCF3/Na2S2O8-Promoted Trifluoromethylthiolation/Cyclization of o-Propargyl Arylazides/ o-Alkynyl Benzylazides: Synthesis of SCF3-Substituted Quinolines and Isoquinolines.

A AgSCF3/Na2S2O8-promoted trifluoromethylthiolation/cascade cyclization of o-propargyl arylazides (or o-alkynyl benzylazides) triggered by a carbon-carbon triple bond is reported. This strategy provides the synthesis of valuable SCF3-substituted quinoline and isoquinoline systems via the construction of one C(sp2)-SCF3 bond and one C-N bond within one process.

Base promoted direct difunctionalization/cascade cyclization of 1,6-enynes.

A novel base-mediated direct difluoroalkylation of 1,6-enynes involving a CF2 radical process has been developed. In the absence of metal catalysts, two different difluoroalkylated cyclization products have been synthesized with good functional group applicability and high stereoselectivity. Notably, the properties of a base have been shown to play a crucial role in the generation selectivity of this transformation.

Recent advances in the tandem reaction of azides with alkynes or alkynols.

Over the past few decades, the development of versatile methodologies to employ azides as aminating agents for the formation of nitrogen-containing compounds has attracted significant attention in synthetic chemistry. This review examines recent developments in the tandem reaction of azides with alkynes and alkynols, which have not been solely discussed before. The formation of diverse nitrogen-containing compounds is classified in this review according to the types of reactions.

Merging photoredox with copper catalysis: decarboxylative difluoroacetylation of α,ß-unsaturated carboxylic acids with ICF2CO2Et.

A photoredox-/copper-catalyzed decarboxylative difluoroacetylation reaction of α,ß-unsaturated carboxylic acids has been developed. This reaction produces a variety of difluoroalkylated alkenes in moderate to excellent yields and exhibits satisfactory stereoselectivity and a broad substrate scope at ambient temperature. Furthermore, this decarboxylative difluoroacetylation protocol provides efficient and environment friendly access to the difluoroalkylated alkenes.

Electrophilic Cyclization of Aryl Propargylic Alcohols: Synthesis of Dihalogenated 6,9-Dihydropyrido[1,2-a]indoles via a Cascade Iodocyclization.

A strategy for the synthesis of 6,9-dihydropyrido[1,2-a]indoles through a cascade iodocyclization of 4-(3-methyl-1H-indol-1-yl)-1,1-diphenylbut-2-yn-1-ol derivatives is presented. This reaction was conducted under very mild conditions and in a short time. The reactions are metal-free, are environmentally friendly and give up to 94% yield. Moreover, the obtained halides allow functional group diversification by palladium-catalyzed coupling reactions, which could act as potential intermediates for the synthesis of valuable compounds.

Copper-catalyzed difluoromethylation of propargylamide-substituted indoles: synthesis of mono- and bis-difluoromethylated indoloazepinone derivatives.

A novel copper-catalyzed difluoromethylation of 2- or 3-propargylamide-substituted indoles with ICF2CO2Et via a radical cascade cyclization process is described. A wide substrate scope is compatible with the reaction conditions to synthesize mono- and bis-difluoromethylated indoloazepinone derivatives, which contain a seven-membered ring.