Regio- and enantiospecific rhodium-catalyzed arylation of unsymmetrical fluorinated acyclic allylic carbonates: inversion of absolute configuration

Nickel-catalyzed electrophiles-controlled enantioselective reductive arylative cyclization and enantiospecific reductive alkylative cyclization of 1,6-enynes

Transition metal-catalyzed asymmetric cyclization of 1,6-enynes is a powerful tool for the construction of chiral nitrogen-containing heterocycles. Despite notable achievements, these transformations have been largely limited to the use of aryl or alkenyl metal reagents, and stereoselective or stereospecific alkylative cyclization of 1,6-enynes remains unexploited. Herein, we report Ni-catalyzed enantioselective reductive anti-arylative cyclization of 1,6-enynes with aryl iodides, providing enantioenriched six-membered carbo- and heterocycles in good yields with excellent enantioselectivities. Additionally, we have realized Ni-catalyzed enantiospecific reductive cis-alkylative cyclization of 1,6-enynes with alkyl bromides, furnishing chiral five-membered heterocycles with high regioselectivity and stereochemical fidelity. Mechanistic studies reveal that the arylative cyclization of 1,6-enynes is initiated by the oxidative addition of Ni(0) to aryl halides and the alkylative cyclization is triggered by the oxidative addition of Ni(0) to allylic acetates. The utility of this strategy is further demonstrated in the enantioselective synthesis of the antiepileptic drug Brivaracetam.

Cobalt-Catalyzed Enantiospecific Dynamic Kinetic Cross-Electrophile Vinylation of Allylic Alcohols with Vinyl Triflates

Asymmetric cross-electrophile coupling has emerged as a promising tool for producing chiral molecules; however, the potential of this chemistry with metals other than nickel remains unknown. Herein, we report a cobalt-catalyzed enantiospecific vinylation reaction of allylic alcohol with vinyl triflates. This work establishes a new method for the synthesis of enantioenriched 1,4-dienes. The reaction proceeds through a dynamic kinetic coupling approach, which not only allows for direct functionalization of allylic alcohols but also is essential to achieve high chemoselectivity. The use of cobalt enables the reactions to proceed with high enantiospecificity, which have failed to be realized by nickel catalysts.

Metal-catalysed C-Het (F, O, S, N) and C-C bond arylation

The formation of C-aryl bonds has been the focus of intensive research over the last decades for the construction of complex molecules from simple, readily available feedstocks. Traditionally, these strategies involve the coupling of organohalides (I, Br, Cl) with organometallic reagents (Mg, Zn, B, Si, Sn,…) such as Kumada-Corriu, Negishi, Suzuki-Miyaura, Hiyama and Sonogashira cross-couplings. More recently, alternative methods have provided access to these products by reactions with less reactive C-Het (F, O, S, N) and C-C bonds. Compared to traditional methods, the direct cleavage and arylation of these chemical bonds, the essential link in accessible feedstocks, has become increasingly important from the viewpoint of step-economy and functional-group compatibility. This comprehensive review aims to outline the development and advances of this topic, which was organized into (1) C-F bond arylation, (2) C-O bond arylation, (3) C-S bond arylation, (4) C-N bond arylation, and (5) C-C bond arylation. Substantial attention has been paid to the strategies and mechanistic investigations. We hope that this review can trigger chemists to discover more efficient methodologies to access arylation products by cleavage of these C-Het and C-C bonds.

Regio- and Diastereoselective Rhodium-Catalyzed Allylic Substitution with Unstabilized Benzyl Nucleophiles

We have developed a highly regio- and diastereoselective rhodium-catalyzed allylic substitution of challenging alkyl-substituted secondary allylic carbonates with benzylzinc reagents, which are prepared from widely available benzyl halides. This process utilizes rhodium(III) chloride as a commercially available, high-oxidation state and bench-stable pre-catalyst to provide a rare example of a regio- and diastereoselective allylic substitution in the absence of an exogenous ligand. This reaction tolerates electronically diverse benzylzinc nucleophiles and an array of functionalized and/or challenging aliphatic allylic electrophiles. Finally, the configurational fluxionality of the rhodium-allyl intermediate is exploited to develop a novel diastereoselective process for the construction of vicinal acyclic ternary/ternary stereogenic centers, in addition to a cyclic ternary/quaternary derivative.

Regio- and Enantioselective Allylic Alkylation of Terminal Alkynes by Synergistic Rh/Cu Catalysis

A highly branch- and enantioselective 1,4-enynes synthesis from readily available terminal alkynes and racemic allylic carbonates by Sonogashira type synergistic Rh and Cu catalysis under neutral conditions has been developed. Aliphatic and aromatic terminal alkynes with various functional groups could be used directly. An inner-sphere reductive elimination C(sp)-C(sp³) bond formation mechanism is supported by the stoichiometric reaction.

Cross-Coupling Reaction of Allylic Ethers with Aryl Grignard Reagents Catalyzed by a Nickel Pincer Complex

A cross-coupling reaction of allylic aryl ethers with arylmagnesium reagents was investigated using β-aminoketonato- and β-diketiminato-based pincer-type nickel(II) complexes as catalysts. An β-aminoketonato nickel(II) complex bearing a diphenylphosphino group as a third donor effectively catalyzed the reaction to afford the target cross-coupled products, allylbenzene derivatives, in high yield. The regioselective reaction of a variety of substituted cinnamyl ethers proceeded to give the corresponding linear products. In contrast, α- and γ-alkyl substituted allylic ethers afforded a mixture of the linear and branched products. These results indicated that the coupling reaction proceeded via a π-allyl nickel intermediate.

Ruthenium-Catalyzed C-H Allylation of Alkenes with Allyl Alcohols via C-H Bond Activation in Aqueous Solution

A robust Ru(II)-catalyzed C-H allylation of electron-deficient alkenes with allyl alcohols in aqueous solution is reported. This method provides a straightforward and efficient access to the synthetically useful 1,4-diene skeletons. With the assistance of the N-methoxycarbamoyl directing group, this allylation reaction features a broad substrate scope with good functional group tolerance, excellent regio- and stereoselectivity, absence of metal oxidants, water-tolerant solvents, and mild reaction conditions. The mechanistic studies indicate that the process of the reversible C-H bond ruthenation is assisted by acetate, and the rate-determining step is unlikely to be the step of C-H bond cleavage.

Regio- and Enantioselective Rhodium-Catalyzed Allylic Alkylation of Racemic Allylic Alcohols with 1,3-Diketones

Highly regio- and enantioselective rhodium-catalyzed allylic alkylation of 1,3-diketones with racemic secondary allylic alcohols is reported. In the presence of a Rh-catalyst derived from the Carreira (P, olefin)-ligand and TFA as an additive, chiral branched α-allylated 1,3-diketones could be obtained in good to excellent yields, with excellent regio- and enantioselectivity ( b/ l > 19/1, 86-98% ee). The direct utilization of allyl alcohols as electrophiles represents an improvement from the viewpoint of an atom economy. Both aryl- and aliphatic-substituted allyl alcohols are suitable substrates with excellent reaction outcomes. This reaction features mild conditions, broad substrate scope, and readily available substrates.

Divergent synthesis of functionalized pyrrolidines and γ-amino ketones via rhodium-catalyzed switchable reactions of vinyl aziridines and silyl enol ethers

Rhodium-catalyzed enantiospecific intermolecular [3+2] cycloadditions and ring-opening reactions of vinylaziridines with silyl enol ethers have been developed to synthesize functionalized pyrrolidines and γ-amino ketones, respectively.

Rhodium-catalyzed intermolecular [3+3] cycloaddition of vinyl aziridines with C,N-cyclic azomethine imines: stereospecific synthesis of chiral fused tricyclic 1,2,4-hexahydrotriazines

A new rhodium-catalyzed intermolecular [3+3] cycloaddition of vinylaziridines with C,N-cyclic azomethine imines has been described to construct enantioenriched 1,2,4-hexahydrotriazines.

Reaction of [TpRh(C2 H4 )2 ] with Dimethyl Acetylenedicarboxylate: Identification of Intermediates of the [2+2+2] Alkyne and Alkyne-Ethylene Cyclo(co)trimerizations

The reaction between the bis(ethylene) complex [TpRh(C2 H4 )2 ], 1, (Tp=hydrotris(pyrazolyl)borate), and dimethyl acetylenedicarboxylate (DMAD) has been studied under different experimental conditions. A mixture of products was formed, in which TpRh(I) species were prevalent, whereas the presence of trapping agents, like water or acetonitrile, allowed for the stabilization and isolation of octahedral TpRh(III) compounds. An excess of DMAD gave rise to a small amount of the [2+2+2] cyclotrimerization product hexamethyl mellitate (6). Although no catalytic application of 1 was achieved, mechanistic insights shed light on the formation of stable rhodium species representing the resting state of the catalytic cycle of rhodium-mediated [2+2+2] cyclo(co)trimerization reactions. Metallacyclopentene intermediate species, generated from the activation of one alkyne and one ethylene molecule from 1, and metallacyclopentadiene species, formed by oxidative coupling of two alkynes to the rhodium centre, are crucial steps in the pathways leading to the final organometallic and organic products.

Nickel-catalyzed asymmetric reductive cross-coupling between vinyl and benzyl electrophiles

A Ni-catalyzed asymmetric reductive cross-coupling between vinyl bromides and benzyl chlorides has been developed. This method provides direct access to enantioenriched products bearing aryl-substituted tertiary allylic stereogenic centers from simple, stable starting materials. A broad substrate scope is achieved under mild reaction conditions that preclude the pregeneration of organometallic reagents and the regioselectivity issues commonly associated with asymmetric allylic arylation.

Enantiospecific, nickel-catalyzed cross-couplings of allylic pivalates and arylboroxines

We have developed an enantiospecific, nickel-catalyzed cross-coupling of unsymmetric 1,3-disubstituted allylic pivalates with arylboroxines. The success of this reaction relies on the use of BnPPh2 as a supporting ligand for the nickel(0) catalyst and NaOMe as a base. This method shows excellent functional group tolerance and broad scope in both the allylic pivalate and arylboroxine, enabling the preparation of 1,3-diaryl allylic products in high yields with excellent levels of regioselectivity and stereochemical fidelity.

Rhodium-catalyzed chemo- and regioselective decarboxylative addition of β-ketoacids to allenes: efficient construction of tertiary and quaternary carbon centers

A rhodium-catalyzed chemo- and regioselective intermolecular decarboxylative addition of β-ketoacids to terminal allenes is reported. Using a Rh(I)/DPPF system, tertiary and quaternary carbon centers were formed with exclusively branched selectivity under mild conditions. Preliminary mechanism studies support that the carbon-carbon bond formation precedes the decarboxylation and the reaction occurs in an outer-sphere mechanism.

Synthesis of 3,3-disubstituted α-tetralones by rhodium-catalysed reaction of 1-(2-haloaryl)cyclobutanols

The rhodium-catalysed reaction of 1-(2-haloaryl)cyclobutanols afforded 3,3-disubstituted α-tetralones. The reaction was applied to the asymmetric synthesis of α-tetralones bearing a chiral quaternary carbon centre at the 3-position, which was otherwise difficult to execute.

Pd-catalyzed regioselective and stereospecific Suzuki-Miyaura coupling of allylic carbonates with arylboronic acids

The Pd-catalyzed Suzuki-Miyaura coupling reaction of unsymmetric 1,3-disubstituted secondary allylic carbonates with arylboronic acids has been developed in a wet solvent under a base-free system to afford allyl-aryl coupling products in a high level of isolated yields with complete regio- and E/Z-selectivities with good to excellent chemoselectivities. The coupling reaction of optically active allyl carbonates gave allyl-aryl coupling products with excellent enantioselectivities with inversion of the stereochemistry. This coupling method was successfully applied to the synthesis of (S)-naproxen.