Preparation of Chiral 3-Arylpyrrolidines via the Enantioselective 1,4-Addition of Arylboronic Acids to Fumaric Esters Catalyzed by Rh(I)/Chiral Diene Complexes

One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

Rhodium(I)/Chiral Diene Complexes Catalyzed Asymmetric Desymmetrization of Alkynyl-Tethered 2,5-Cyclohexadienones Through an Arylative Cyclization Cascade

Cis-hydrobenzofurans, cis-hydroindoles, and cis-hydrindanes, privileged structural motifs found in numerous biologically active natural and synthetic compounds, are efficiently prepared by a Rh(I)-catalyzed cascade syn-arylation/1,4-addition protocol. This approach starts with the regioselective syn-arylation of the alkyne tethered to 2,5-hexadienone moieties, using a chiral Rh(I) catalyst generated in situ from a chiral bicyclo[2.2.1]hepatadiene ligand L4f. By forging two new carbon-carbon bonds and introducing two chiral centers, the resulting alkenylrhodium species undergoes desymmetrization via an intramolecular 1,4-addition reaction, delivering annulated products with high yields and enantioselectivities.

Chiral Diene Ligands in Asymmetric Catalysis

Asymmetric catalysis has emerged as a general and powerful approach for constructing chiral compounds in an enantioselective manner. Hence, developing novel chiral ligands and catalysts that can effectively induce asymmetry in reactions is crucial in modern chemical synthesis. Among such chiral ligands and catalysts, chiral dienes and their metal complexes have received increased attention, and a great progress has been made over the past two decades. This review provides comprehensive and critical information on the essential aspects of chiral diene ligands and their importance in asymmetric catalysis. The literature covered ranges from August 2003 (when the first effective chiral diene ligand for asymmetric catalysis was reported) to October 2021. This review is divided into two parts. In the first part, the chiral diene ligands are categorized according to their structures, and their preparation methods are summarized. In the second part, their applications in asymmetric transformations are presented according to the reaction types.

Palladium-Catalyzed Asymmetric Hydroesterification of α-Aryl Acrylic Acids to Chiral Substituted Succinates

A palladium-catalyzed asymmetric hydroesterification of α-aryl acrylic acids with CO and alcohol was developed, preparing a variety of chiral α-substituted succinates in moderate yields with high ee values. The kinetic profile of the reaction progress revealed that the alkene substrate first underwent the hydroesterification followed by esterification with alcohol. The origin of the enantioselectivity was elucidated by density functional theory computation.

Application of Rh(I)/Bicyclo[2.2.1]heptadiene Catalysts to the Enantioselective Synthesis of Chiral Amines

The development of efficient synthetic methods for accessing enantioenriched α-chiral amines is of great importance in the disciplines of medicinal and synthetic organic chemistry. Enantioselective Rh-catalyzed 1,2-addition reactions to activated imine derivatives are regarded as useful protocols for forming α-chiral amines. This personal account outlines our efforts to develop chiral bicyclo[2.2.1]heptadiene ligands for Rh-catalyzed asymmetric additions of various organoboron reagents to a wide range of imine derivatives. Transformations of the thus-obtained adducts into known natural products or molecules of pharmaceutical importance serve to confirm their synthetic usefulness.

α-Boryl Organometallic Reagents in Catalytic Asymmetric Synthesis

Recent years have witnessed an increase in the popularity of α-boryl organometallic reagents as versatile nucleophiles in asymmetric synthesis. These compounds have been adopted in chemo- and stereoselective coupling reactions with a number of different electrophiles. The resulting enantioenriched boronic esters can be applied in stereospecific carbon-carbon or carbon-heteroatom bond construction reactions, enabling a two-step strategy for the construction of complex structures with high efficiency and functional group compatibility. Due to these reasons, tremendous effort has been devoted to the preparation of enantiomerically enriched α-boryl organometallic reagents and to the development of stereoselective reactions of related racemic or prochiral materials. In this review, we describe the enantio- or diastereoselective reactions that involve α-boryl organometallic reagents as starting materials or products and we showcase their synthetic utility.

Convergent Evolution of Diastereomeric Mixtures of 5-Methoxy-pentylzirconocenes toward Trans-1,2-substituted Cyclopentanes

The access to 1,2- and 1,1,2-substituted trans cyclopentanes via a sequential hydrozirconation/TMSOTf-mediated cyclization applied to 5-methoxypent-1-enes is presented. Involving a transient carbocation, the reaction was shown to be diastereo-convergent. Possibly performed in a nonracemic version, the reaction proved compatible with a range of functional groups affording a large panel of cyclopentanes.

Cooperative asymmetric reactions combining photocatalysis and enzymatic catalysis

Living organisms rely on simultaneous reactions catalysed by mutually compatible and selective enzymes to synthesize complex natural products and other metabolites. To combine the advantages of these biological systems with the reactivity of artificial chemical catalysts, chemists have devised sequential, concurrent, and cooperative chemoenzymatic reactions that combine enzymatic and artificial catalysts^1-9. Cooperative chemoenzymatic reactions consist of interconnected processes that generate products in yields and selectivities that cannot be obtained when the two reactions are carried out sequentially with their respective substrates^2,7. However, such reactions are difficult to develop because chemical and enzymatic catalysts generally operate in different media at different temperatures and can deactivate each other^1-9. Owing to these constraints, the vast majority of cooperative chemoenzymatic processes that have been reported over the past 30 years can be divided into just two categories: chemoenzymatic dynamic kinetic resolutions of racemic alcohols and amines, and enzymatic reactions requiring the simultaneous regeneration of a cofactor^2,4,5. New approaches to the development of chemoenzymatic reactions are needed to enable valuable chemical transformations beyond this scope. Here we report a class of cooperative chemoenzymatic reaction that combines photocatalysts that isomerize alkenes with ene-reductases that reduce carbon-carbon double bonds to generate valuable enantioenriched products. This method enables the stereoconvergent reduction of E/Z mixtures of alkenes or reduction of the unreactive stereoisomers of alkenes in yields and enantiomeric excesses that match those obtained from the reduction of the pure, more reactive isomers. The system affords a range of enantioenriched precursors to biologically active compounds. More generally, these results show that the compatibility between photocatalysts and enzymes enables chemoenzymatic processes beyond cofactor regeneration and provides a general strategy for converting stereoselective enzymatic reactions into stereoconvergent ones.

A N,N'-dioxide/Mg(OTf)2 complex catalyzed enantioselective α-addition of isocyanides to alkylidene malonates

A simple and efficient catalytic asymmetric α-addition of isocyanides to alkylidene malonates was realized using a chiral N,N′-dioxide/Mg^II catalyst. A variety of 2-alkyl-5-aminoxazoles were obtained in up to 99% yield and 96% ee, and could be converted to imides and dipeptides.

A highly efficient catalytic asymmetric α-addition of isocyanides to alkylidene malonates was accomplished. The process was based on the utilization of a chiral N,N′-dioxide/Mg^II catalyst, delivering a variety of 2-alkyl-5-aminooxazoles in up to 99% yield and 96% ee under mild reaction conditions. Besides, a chiral imide and dipeptide could be easily obtained by ring-opening of the oxazole product, both of which are important structural motifs for many biologically active compounds. Based on the experimental investigations and previous work, a possible transition state model was proposed.

Synthesis and determination of absolute configuration of a non-peptidic αvβ6 integrin antagonist for the treatment of idiopathic pulmonary fibrosis

Integrin inhibitor (cell adhesion assays) pIC₅₀ α_vβ₆ = 8.4, α_vβ₃ = 6.0, α_vβ₅ = 5.9 and α_vβ₈ = 7.7.

A second-generation ligand for the enantioselective rhodium-catalyzed addition of arylboronic acids to alkenylazaarenes

A 2,4,6-trialkylanilide-containing chiral diene has been identified as a superior ligand for the enantioselective rhodium-catalyzed arylation of alkenylazaarenes with arylboronic acids.