Enantioselective Hydroalkenylation of Olefins with Enol Sulfonates Enabled by Dual Copper Hydride and Palladium Catalysis

Enantioselective Hydroalkenylation and Hydroalkynylation of Alkenes Enabled by a Transient Directing Group: Catalyst Generality through Rigidification

The catalytic enantioselective synthesis of α-chiral alkenes and alkynes represents a powerful strategy for rapid generation of molecular complexity. Herein, we report a transient directing group (TDG) strategy to facilitate site-selective palladium-catalyzed reductive Heck-type hydroalkenylation and hydroalkynylation of alkenylaldehyes using alkenyl and alkynyl bromides, respectively, allowing for construction of a stereocenter at the δ-position with respect to the aldehyde. Computational studies reveal the dual beneficial roles of rigid TDGs, such as L-tert-leucine, in promoting TDG binding and inducing high levels of enantioselectivity in alkene insertion with a variety of migrating groups.

Regioselective Hydroalkylation of Vinyl- and Allylsilanes as Well as Vinylgermanes under Ni-H Catalysis

A Ni-H-catalyzed hydroalkylation of vinylsilanes and -germanes as well as allylsilanes with unactivated alkyl iodides is reported. Unlike related reactions of styrene or vinyl boronate esters, the addition across the C-C double bond proceeds with anti-Markovnikov selectivity to deliver the linear regioisomer. Mechanistic control experiments support a radical mechanism, and a competition experiment reveals that the chemoselectivity is in favor of the vinyl over the allyl group.

Multimetallic-Catalyzed C-C Bond-Forming Reactions: From Serendipity to Strategy

The use of two or more metal catalysts in a reaction is a powerful synthetic strategy to access complex targets efficiently and selectively from simple starting materials. While capable of uniting distinct reactivities, the principles governing multimetallic catalysis are not always intuitive, making the discovery and optimization of new reactions challenging. Here, we outline our perspective on the design elements of multimetallic catalysis using precedent from well-documented C-C bond-forming reactions. These strategies provide insight into the synergy of metal catalysts and compatibility of the individual components of a reaction. Advantages and limitations are discussed to promote further development of the field.

A General Strategy for the Asymmetric Preparation of α-Stereogenic Allyl Silanes, Germanes, and Boronate Esters via Dual Copper Hydride- and Palladium-Catalysis

α-Stereogenic allyl metalloids are versatile synthetic intermediates which can undergo various stereocontrolled transformations. Most existing methods to prepare α-stereogenic allyl metalloids involve multi-step sequences that curtail the number of compatible substrates and are limited to the synthesis of boronates. Here, we report a general method for the enantioselective preparation of α-stereogenic allyl metalloids utilizing dual CuH- and Pd-catalysis. This approach leverages a stereoretentive Cu-to-Pd transmetalation of an in situ generated alkyl copper species to allow access to enantioenriched allyl silanes, germanes, and boronate esters with broad functional group compatibility.

Access to dialkylated allylic stereogenic centers by Ni-catalysed enantioselective hydrovinylation of unactivated alkenes

Tertiary dialkylated allylic stereogenic centers are widespread substructures in bioactive molecules and natural products. However, enantioselective access to dialkyl substituted allylic motifs remains a long-term challenge. Herein, a straightforward protocol to build allylic dialkylated stereogenic centers enabled by nickel-catalysed regio- and enantioselective hydrovinylation of isolated unactivated alkenes facilitated by a weakly coordinating group with vinyl bromides was developed, affording dialkylated allylic species in good yields with excellent enantioselectivities. The reaction distinguishes distinct alkenes and works for both terminal and internal aliphatic alkenes. The reaction proceeds under mild conditions and tolerates a wide range of functional groups.

Recent Applications on Dual-Catalysis for C–C and C–X Cross-Coupling Reactions

Coupling reactions stand amid the most significant reactions in synthetic organic chemistry. Of late, these coupling strategies are being viewed as a versatile synthetic tool for a wide range of organic transformations in many sectors of chemistry, ranging from indispensable synthetic scaffolds and natural products of biological significance to novel organic materials. Further, the use of dual-catalysis in accomplishing various interesting cross-coupling transformations is an emerging field in synthetic organic chemistry, owing to their high catalytic performance rather than the use of a single catalyst. In recent years, synthetic organic chemists have given considerable attention to hetero-dual catalysis; wherein these catalytic systems have been employed for the construction of versatile carbon–carbon [C(sp 3)–C(sp 3), C(sp 3)–C(sp 2), C(sp 2)–C(sp 2)] and carbon–heteroatom (C–N, C–O, C–P, C–S) bonds. Therefore, in this mini-review, we are emphasizing recently developed various cross-coupling reactions catalysed by transition-metal dual-catalysis (i.e., using palladium and copper catalysts, but omitting the reports on photoredox/metal catalysis).

1 Introduction

2 Cu/Pd-Catalysed Bond Formation

2.1 Pd/Cu-Catalysed C(sp 3)–C(sp 2) Bond Formation

2.2 Pd/Cu-Catalysed C(sp 2)–C(sp 2) Bond Formation

2.3 Pd/Cu-Catalysed C(sp)–C(sp 2) Bond Formation

2.4 Pd/Cu-Catalysed C(sp 3)–C(sp 3) Bond Formation

2.5 Pd/Cu-Catalysed C–X (X = B, N, P, S, Si) Bond Formation

3 Conclusion

Enantioselective Hydrocarbamoylation of Alkenes

The asymmetric hydroaminocarbonylation of olefins represents a straightforward approach for the synthesis of enantioenriched amides, but is hampered by the necessity to employ CO gas, often at elevated pressures. We herein describe, as an alternative, an enantioselective hydrocarbamoylation of alkenes leveraging dual copper hydride and palladium catalysis to enable the use of readily available carbamoyl chlorides as a practical carbamoylating reagent. The protocol is applicable to various types of olefins, including alkenyl arenes, terminal alkenes, and 1,1-disubstituted alkenes. Substrates containing a diverse range of functional groups as well as heterocyclic substructures undergo functionalization to provide α- and β-chiral amides in good yields and with excellent enantioselectivities.

Highly Regioselective Copper-Catalyzed Transfer Hydrodeuteration of Unactivated Terminal Alkenes

Catalytic transfer hydrodeuteration of unactivated alkenes is challenging because of the requirement that chemically similar hydrogen and deuterium undergo selective insertion across a π-bond. We now report a highly regioselective catalytic transfer hydrodeuteration of unactivated terminal alkenes across a variety of heteroatom- or heterocycle-containing substrates. The base-metal-catalyzed reaction is also demonstrated on two complex natural products. Reaction studies indicate modular conditions that can also be extended to perform either an alkene transfer hydrogenation or transfer deuteration.

A Dual CuH- and Pd-Catalyzed Stereoselective Synthesis of Highly Substituted 1,3-Dienes

Conjugated dienes are versatile building blocks and prevalent substructures in synthetic chemistry. Herein, we report a method for the stereoselective hydroalkenylation of alkynes, utilizing readily available enol triflates. We leveraged an in situ-generated and geometrically pure vinyl-Cu(I) species to form the Z,Z- or Z,E-1,3-dienes in excellent stereoselectivity and yield. This approach allowed for the synthesis of highly substituted Z-dienes, including pentasubstituted 1,3-dienes, which are difficult to prepare by existing approaches.

Enantio- and Diastereodivergent Synthesis of Spirocycles through Dual-Metal-Catalyzed [3+2] Annulation of 2-Vinyloxiranes with Nucleophilic Dipoles

The development of efficient and straightforward methods for obtaining all optically active isomers of structurally rigid spirocycles from readily available starting materials is of great value in drug discovery and chiral ligand development. However, the stereodivergent synthesis of spirocycles bearing multiple stereocenters remains an unsolved challenge owing to steric hindrance and ring strain. Herein, we report an enantio- and diastereodivergent synthesis of rigid spirocycles through dual-metal-catalyzed [3+2] annulation of oxy π-allyl metallic dipoles with less commonly employed nucleophilic dipoles (imino esters). A series of spiro compounds bearing a pyrroline and an olefin were easily synthesized in an enantio- and diastereodivergent manner (up to 19:1 dr, >99 % ee), which showed great promise as a new type of N-olefin ligand. Preliminary mechanistic studies were also carried out to understand the process of this bimetallic catalysis.

Regioselective Hydroalkylation of Vinylarenes by Cooperative Cu and Ni Catalysis

Disclosed here is a dual copper and nickel catalytic system with a silyl hydride source for promoting the linear selective hydroalkylation of vinylarenes. This carbon-carbon bond-forming protocol is applied to couple a variety of functionalized vinylarenes with alkyl halides applying a nickel(II) NNN pincer complex in the presence of an NHC-ligated copper catalyst. This combination allows for a 1 mol % loading of the nickel catalyst leading to turnover numbers of up to 72. Over 40 examples are presented, including applications for pharmaceutical diversification. Labeling experiments demonstrated the regioselectivity of the reaction and revealed that the copper catalyst plays a crucial role in enhancing the rate for formation of the reactive linear alkyl nickel complex. Overall, the presented work provides a complimentary approach for hydroalkylation reactions, whilst providing a preliminary mechanistic understanding of the cooperativity between the copper and nickel complexes.