Palladium-Catalyzed Heck/Suzuki Tandem Reaction of (Z)-1-Iodo-1,6-dienes and Organoboronic Acids

The Heck/Suzuki tandem reaction has emerged as an essential strategy for the synthesis of complex molecules. Herein, an efficient palladium-catalyzed Heck/Suzuki tandem reaction of (Z)-1-iodo-1,6-dienes with organoboronic acids is described, providing various tetrahydropyridines in good to excellent yields under mild reaction conditions. The key to the success of this approach is the avoidance of the intramolecular second Heck insertion occurring prior to the transmetalation step. In addition, the asymmetric version of this reaction is investigated to deliver chiral tetrahydropyridine in excellent yield with promising enantioselectivity.

Sadphos as Adaptive Ligands in Asymmetric Palladium Catalysis

ConspectusPalladium catalysis, as one of the most important strategies in asymmetric synthesis, has continuously attracted the attention of organic chemists. With the development of chiral ligands, increasingly challenging reactions and substantial progress in asymmetric catalysis are being realized.Since 2014, we have focused on exploiting a series of sulfinamide phosphine ligands called "Sadphos," including Ming-Phos, Xu-Phos, Xiao-Phos, Xiang-Phos, TY-Phos, PC-Phos, GF-Phos, and WJ-Phos. These ligands can be easily prepared in two to four steps using commercial materials. These new types of ligands have shown remarkable performance in transition-metal-catalyzed reactions, especially in Pd-catalyzed transformations. X-ray diffraction analysis, mechanistic studies, and density functional theory calculations have revealed that Sadphos ligands can coordinate with the Pd0 and PdII species in the Pd0/P, Pd0/P,S, or PdII/P,O modes.This Account summarizes our recent efforts toward palladium-catalyzed enantioselective reactions using Sadphos ligands. These ligands were found to be privileged and very crucial to promote the reactions by increasing the reactivity and enantioselectivity. Ming-Phos is an effective ligand in Pd-catalyzed asymmetric coupling and intramolecular Heck reactions, providing highly enantioselective trisubstituted allenes, axially chiral anilides, gem-diarylmethine silanes, and disubstituted dihydroisoquinolinones. Incorporation of an electron-rich cyclohexyl group in the phosphine moiety afforded Xu-Phos, which showed a unique effect in a series of asymmetric transformations, including reductive Heck, dearomative Mizoroki-Heck, tandem Heck/Suzuki coupling, carboiodination, carboamination, and cross-coupling reactions. Using a similar strategy, our group synthesized more electron-rich TY-Phos and Xiang-Phos ligands bearing t-butyl and 1-adamantyl group at P atoms, respectively. Regarding stereoelectronic features, these two characteristic ligands were the best choice to satisfy the requirements of the palladium-catalyzed fluoroarylation of gem-difluoroalkenes, intermolecular α-arylation of aldehydes, carboetherification of alkenyl oximes, and carboheterofunctionalization of 2,3-dihydrofurans. Compared with the aforementioned Sadphos ligands, the attractive features of Xiao-Phos, including high nucleophilicity originating from the CH2PPh2 group and the ortho-substituent effect at the side of the aryl ring, are presumably responsible for its efficiency. The Pd/Xiao-Phos catalyst system shows good performance in a series of cross-coupling reactions of secondary phosphine oxides, affording P-stereogenic products bearing multiple types of molecular skeletons. The modification of the basic Sadphos backbone by introducing a xanthene skeleton motivated us to design and synthesize monophosphines, named PC-Phos and GF-Phos. PC-Phos is effective in various reactions, including arylation of sulfenate anions, denitrogenative cyclization of benzotriazoles, and dearomatization of indoles. The practicability of GF-Phos was validated in the Pd-catalyzed asymmetric three-component coupling of N-tosylhydrazones, aryl halides, and terminal alkynes, as well as in the cross-coupling of N-tosylhydrazones and vinyl iodides with pendent amines. In addition, ferrocene-derived WJ-Phos was employed in the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction, affording axially chiral biaryl monophosphine oxides in excellent enantiomeric excesses.

Recent advances in Pd-catalyzed asymmetric cyclization reactions

Over the past few decades, there have been major developments in transition metal-catalyzed asymmetric cyclization reactions, enabling the convenient access to a wide spectrum of structurally diverse chiral carbo- and hetero-cycles, common skeletons found in fine chemicals, natural products, pharmaceuticals, agrochemicals, and materials. In particular, a plethora of enantioselective cyclization reactions have been promoted by chiral palladium catalysts owing to their outstanding features. This review aims to collect the latest advancements in enantioselective palladium-catalyzed cyclization reactions over the past eleven years, and it is organized into thirteen sections depending on the different types of transformations involved.

Palladium-Catalyzed Carbonylative Hiyama-Denmark Reaction toward the Synthesis of Aryl Carbonyl-Containing Oxindoles

A palladium-catalyzed domino Heck cyclization/carbonylative Hiyama-Denmark cross-coupling reaction between alkene-tethered aryl iodides and silylcarboxylic acids is presented. This reaction proceeds well without toxic carbon monoxide (CO) gas and has good functional group tolerance, providing an alternative access to carbonyl-containing oxindoles. In this transformation, silylcarboxylic acids play a dual role as a CO source and a nucleophile.

Palladium(II)-catalyzed enantioselective intermolecular oxidative diarylation of internal enamides

The construction of vicinal stereogenic centers via the simultaneous formation of two C-C bonds across alkenes under oxidative conditions is a stubborn challenge. Herein, we report a Pd(II)-catalyzed highly enantioselective intermolecular oxidative 1,2-diarylation reaction of internal enamides with aryl boronic acids, enabling the expedient construction of two vicinal stereocenters with excellent diastereo-, and enantioselectivities.

Catalytic Asymmetric Diarylation of Internal Acyclic Styrenes and Enamides

Enantioselective transformations of olefins are among the most important strategies for the asymmetric synthesis of organic compounds. Chemo-, diastereo-, and stereoselective control of reactions with internal acyclic alkenes for the construction of functionalized acyclic alkanes still remain a persistent challenge. Here, we report a palladium-catalyzed asymmetric regiodivergent Heck-type diarylation of internal acyclic alkenes. The 1,2-diarylation of two accessible acyclic alkenes, cinnamyl carbamates and enamides with diazonium salts and aromatic boronic acids, furnishes products containing vicinal stereogenic centers via the stereospecific formation of carbonyl coordination-assisted transient palladacycles. Moreover, the asymmetric migratory diarylation of enamides enables the formation of incontiguous stereocenters by an interrupted diastereoselective 1,3-chain-walking process. This protocol streamlines access to highly functionalized multisubstituted enantioenriched carbamates and amine derivatives which are embedded in the key biologically active motifs.

endo-5-Norbornene-2,3-dimethanol-promoted asymmetric Heck/Suzuki cascade reaction of N-(2-bromophenyl)acrylamides

An endo-5-norbornene-2,3-dimethanol-promoted highly enantioselective palladium-catalyzed Heck/Suzuki cascade reaction of N-(2-bromophenyl)acrylamides has been developed.

Palladium-catalyzed Heck cyclization/allylation with homoallyl alcohols via retro-allylation

A palladium-catalyzed reaction of aryl iodide-tethered alkenes with homoallyl alcohols is reported, providing a convenient and efficient approach to C(sp3)–allylation products.

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.

Sequential Pd0 - and PdII -Catalyzed Cyclizations: Enantioselective Heck and Nucleopalladation Reactions

An enantioselective consecutive cyclization/coupling process, catalyzed by palladium is reported. Stereoinduction arises from an enantioselective carbopalladation, generating an intermediate which promotes a nucleopalladation step. The dual cyclization sequence was compatible with a variety of alkyne-tethered oxygen- and nitrogen-centered nucleophiles, and a variety of alkenyl-tethered aryl iodides, to forge numerous bisheterocycles in good yields and high regio- and enantioselectivities.

Synthesis of Arylidene-β-lactams via exo-Selective Matsuda-Heck Arylation of Methylene-β-lactams

exo-Methylene-β-lactams were synthesized in two steps from commercially available 3-bromo-2-(bromomethyl)propionic acid and reacted with arene diazonium salts in a Heck-type arylation in the presence of catalytic amounts of Pd(OAc)₂ under ligand-free conditions. The products, arylidene-β-lactams, were obtained in high yields as single isomers. The β-hydride elimination step of the Pd-catalyzed coupling reaction proceeds with high exo-regioselectivity and E-stereoselectivity. With aryl iodides, triflates, or bromides, the coupling products were isolated only in low yields, due to extensive decomposition of the starting material at elevated temperatures. This underlines that arene diazonium salts can be superior arylating reagents in Heck-type reactions and yield coupling products in synthetically useful yields and selectivities when conventional conditions fail.

Pd-Catalyzed Enantioselective Dicarbofunctionalization of Alkene to Access Disubstituted Dihydroisoquinolinone

A Pd/Xu-Phos-catalyzed asymmetric Heck/Suzuki domino reaction has been developed that shows high functional group tolerance and enables coupling with various aryl/alkenyl borates. A series of chiral disubstituted dihydroisoquinolinones could be obtained in good yields and excellent enantioselectivities.

Enantioselective CO2 Fixation Via a Heck-Coupling/Carboxylation Cascade Catalyzed by Nickel

A novel asymmetric nickel-based procedure has been developed in which CO₂ fixation is achieved as a second step of a truncated Heck coupling. For this, a new chiral ligand has been prepared and shown to achieve enantiomeric excesses up to 99 %. The overall process efficiently furnishes chiral 2,3-dihydrobenzofuran-3-ylacetic acids, an important class of bioactive products, from easy to prepare starting materials. A combined experimental and computational effort revealed the key steps of the catalytic cycle and suggested the unexpected participation of Ni(I) species in the coupling event.

Copper-catalyzed enantioselective arylboronation of activated alkenes leading to chiral 3,3′-disubstituted oxindoles

Copper-catalyzed asymmetric arylboronation of activated alkenes for producing highly enantioenriched 3-boroalkyl oxindoles and incorporating pharmacophores is depicted.

Asymmetric synthesis of 3-benzyl and allyl isoindolinones by Pd-catalyzed dicarbofunctionalization of 1,1-disubstituted enamides

The Pd-catalyzed enantioselective Heck/Suzuki reaction of 1,1-disubstituted enamides with aryl/vinyl boronic acids has been developed to access 3-benzyl/allyl substituted isoindolinones bearing a tetrasubstituted stereogenic carbon center.

Recent developments in asymmetric Heck type cyclization reactions for constructions of complex molecules

Intramolecular carbometallation-initiated asymmetric transformations are a general and powerful approach for the construction of carbo- and heterocyclic systems with one and more stereocenters. In addition, the newly developed multiple cascade reactions are an attractive strategy for increasing the molecular complexity in one step. In recent years, great progress has been made in this area with the use of various palladium and nickel complexes with P- and N-donor chiral ligands. This review highlights recent developments in intramolecular asymmetric Heck reactions, reductive Heck reactions and various types of cascade transformations (intramolecular Heck/Heck, Heck/nucleophilic trapping, Heck/Tsuji-Trost, Heck/Suzuki-Miyaura, Heck/Sonogashira, and Heck/carbonylation) in the synthesis of complex molecules over the past 5 years. A number of examples from before 2016 are included as background information. Particular attention is paid to the use of inexpensive nickel complexes as highly efficient catalysts for a number of asymmetric reactions considered here. A perspective on current challenges and potential future developments in the field of asymmetric Heck type cyclizations is also provided.

Nickel-catalyzed enantioselective reductive carbo-acylation of alkenes

Recently, transition-metal-catalyzed asymmetric dicarbofunctionalization of tethered alkenes has emerged as a powerful method for construction of chiral cyclic carbo- and heterocycles. However, all these reactions rely on facially selective arylmetalation of the pendant olefinic unit. Here, we successfully apply acylnickelation as the enantiodetermining step in the asymmetric nickel-catalyzed reductive carbo-acylation of aryl carbamic chloride-tethered alkenes with primary and secondary alkyl iodides as well as benzyl chlorides as the coupling partners, using manganese as a reducing agent. By circumventing the use of pre-generated organometallics, this reductive strategy enables the synthesis of diverse enantioenriched oxindoles bearing a quaternary stereogenic center under mild reaction conditions with high tolerance of a broad range of functional moieties.