Palladium-catalyzed enantioselective carbonylation reactions

Synthesis of Multisubstituted 2,3-Allenamides via Palladium-Catalyzed Carbonylation of Propargylic Esters

2,3-Allenamides are an important class of unsaturated group-substituted carbonyl compounds. A palladium-catalyzed aminocarbonylation of propargyl acetates with amines for the synthesized tri-/tetrasubstituted 2,3-allenamides has been developed. A broad range of tri-/tetrasubstituted 2,3-allenamides have been prepared from propargyl acetates in good to excellent yields. The reaction featured mild reaction conditions and good functional group tolerance. The applicability of this methodology was further highlighted by the late-stage modification of several natural products and pharmaceuticals.

Umpolung-Enabled Divergent Dearomative Carbonylations

Although dearomative functionalizations enable the direct conversion of flat aromatics into precious three-dimensional architectures, the case for simple arenes remains largely underdeveloped owing to the high aromatic stabilization energy. We herein report a dearomative sequential addition of two nucleophiles to arene π-bonds through umpolung of chromium-arene complexes. This mode enables divergent dearomative carbonylation reactions of benzene derivatives by tolerating various nucleophiles in combination with alcohols or amines under CO-gas-free conditions, thus providing modular access to functionalized esters or amides. The tunable synthesis of 1,3- or 1,4-cyclohexadienes as well as the construction of carbon quaternary centers further highlight the versatility of this dearomatization. Diverse late-stage modifications and derivatizations towards synthetically challenging and bioactive molecules reveal the synthetic utility. A possible mechanism was proposed based on control experiments and intermediate tracking.

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.

Cobalt-Catalyzed Enantioselective C-H Carbonylation towards Chiral Isoindolinones

Transition metal-catalyzed enantioselective C-H carbonylation with carbon monoxide, an essential and easily available C1 feedstock, remains challenging. Here, we disclosed an unprecedented enantioselective C-H carbonylation catalyzed by inexpensive and readily available cobalt(II) salt. The reactions proceed efficiently through desymmetrization, kinetic resolution, and parallel kinetic resolution, affording a broad range of chiral isoindolinones in good yields with excellent enantioselectivities (up to 92 % yield and 99 % ee). The synthetic potential of this method was demonstrated by asymmetric synthesis of biological active compounds, such as (S)-PD172938 and (S)-Pazinaclone. The resulting chiral isoindolinones also serve as chiral ligands in cobalt-catalyzed enantioselective C-H annulation with alkynes to construct phosphorus stereocenter.

Palladium-Catalyzed Dual C-H Carbonylation of Diarylamines Leading to Diversified Acridones under CO-Free Conditions

A Pd-catalyzed dual C-H carbonylation of commercially available diarylamines using Co2(CO)8 as a safe CO source has been developed. This methodology provides a facile approach for the synthesis of diversified acridones in moderate to good yields. The protocol features good functional group compatibility, operational safety, easy scale-up, and versatile transformations.

Enantioselective Palladium-Catalyzed Domino Carbonylative Heck Esterification of o-Iodoalkenylbenzenes with Arylboronic Acids

The current investigation presents an innovative palladium-catalyzed asymmetric carbonylative Heck esterification method. This approach facilitates the efficient synthesis of various chiral γ-ketoacid esters by utilizing o-alkenyliodobenzenes and arylboronic acids as primary substrates. This reaction achieves the creation of three carbon-carbon bonds, two carbon-oxygen bonds, and the establishment of a quaternary carbon center within a single step. The α-chiral γ-ketoacid esters were obtained in yields ranging from good to high yields, displaying enantiomeric excesses (ee's) levels up to 92% under mild reaction conditions.

Carbonylative Transformations Using a DMAP-Based Pd-Catalyst through Ex Situ CO Generation

A phosphine-free, efficient protocol for aminocarbonylation and carbonylative Suzuki-Miyaura coupling has been developed using a novel palladium complex, [PdII(DMAP)2(OAc)2]. The complex was successfully synthesized using a stoichiometric reaction between PdII(OAc)2 and DMAP in acetone at room temperature and characterized using single-crystal X-ray analysis. Only 5 mol % catalyst loading was sufficient for effective carbonylative transformations. "Chloroform-COware" chemistry was utilized for safe and facile insertion of the carbonyl unit using chloroform as an inexpensive CO source in a two-chamber setup. Various value-added pharmaceutically relevant compounds such as CX-516, CX-546, and farampator were synthesized using the technique. Furthermore, the commercially designed COware was engineered to COware-RB setup for sequential one-pot synthesis of indenoisoquinolines (topoisomerase I inhibitors).

Photo-thermal Cooperative Carbonylation of Ethanol with CO2 on Cu2 O-SrTiCuO3-x

Carbonylation of ethanol with CO2 as carbonyl source into value-added esters is of considerable significance and interest, while remains of great challenge due to the harsh conditions for activation of inert CO2 in that the harsh conditions result in undesired activation of α-C-H and even cleavage of C-C bond in ethanol to deteriorate the specific activation of O-H bond. Herein, we propose a photo-thermal cooperative strategy for carbonylation of ethanol with CO2 , in which CO2 is activated to reactive CO via photo-catalysis with the assistance of *H from thermally-catalyzed dissociation of alcoholic O-H bond. To achieve this proposal, an interfacial site and oxygen vacancy both abundant SrTiCuO3-x supported Cu2 O (Cu2 O-SrTiCuO3-x ) has been designed. A production of up to 320 μmol g-1  h-1 for ethyl formate with a selectivity of 85.6 % to targeted alcoholic O-H activation has been afforded in photo-thermal assisted gas-solid process under 3.29 W cm-1 of UV/Vis light irradiation (144 °C) and 0.2 MPa CO2 . In the photo-driven activation of CO2 and following carbonylation, CO2 activation energy decreases to 12.6 kJ mol-1 , and the cleavage of alcoholic α-C-H bond has been suppressed.

Visible Light-Accelerated Palladium-Catalyzed Thiocarbonylation Using Oxalic Acid Monothioester with Aryl/Alkenyl Sulfonium Salts

Herein, we present a decarboxylative thiocarbonylation of aryl and alkenyl sulfonium salts with oxalic acid monothioethers (OAMs), which can be achieved by visible light-accelerated palladium catalysis. Sulfonium salts are widely available, and OAM is an easily accessible and stored reagent; this mild reaction method can also be used for the synthesis of different types of thioester compounds. The reaction represents a new application of visible light-accelerated palladium catalysis in catalytic decarboxylative cross-couplings.

Photoinduced Five-Component Radical Relay Aminocarbonylation of Alkenes

Radical single carbonylation reactions with CO constitute a direct and robust strategy toward various carbonyl compounds from readily available chemicals, and have been extensively studied over the past decades. However, realizing highly selective catalytic systems for controlled radical double carbonylation reactions has remained a substantial challenge, particularly for the more advanced multicomponent variants, despite their great potential value. Herein, we report a visible-light-driven radical relay five-component radical double aminocarbonylation reaction of unactivated alkenes using CO under metal-free conditions. This protocol provides direct access to valuable γ-trifluoromethyl α-ketoamides with good yields and high chemoselectivity. Crucial was the identification of distinct dual roles of amine coupling partners, sequentially acting as electron donors for the formation of photoactive electron donor-acceptor (EDA) complexes with radical precursors and then as a CO acceptor via nitrogen radical cations to form carbamoyl radicals. Cross-coupling of carbamoyl radicals with the acyl radicals that are formed in an alkene-based relay process affords double aminocarbonylation products.

Asymmetric construction of phosphono dihydropyranones from α-ketophosphonates enabled by Pd/chiral isothiourea relay catalysis

A highly enantio- and diastereoselective approach has been developed for the synthesis of chiral phosphono dihydropyranones. This approach is enabled by Pd/chiral isothiourea relay catalysis under mild reaction conditions, starting from readily available benzyl bromides, CO, and α-ketophosphonates. The cascade reaction involves the generation of a ketene intermediate from Pd-catalyzed carbonylation of benzyl bromide and subsequent chiral Lewis base catalyzed formal [4 + 2] reaction. Phosphono lactone products can also be transformed to chiral 1,5-diester products in good yield and high stereoselectivity.

Palladium-Catalyzed Carbonylative Dearomatization of Indoles to Achieve Carbonyl-Containing Spirocyclic Indolenines Bearing an All-Carbon Quaternary Center

A Pd-catalyzed carbonylative dearomatization via an acyl Pd complex has been developed. Diversified carbonyl-containing spirocyclic indolenines with an all-carbon quaternary center were constructed in an efficient and straightforward way with good to excellent yields. The protocol features a simple catalytic system, operational simplicity, a broad substrate scope, easy scale-up, and versatile transformations. In addition, the asymmetric reaction was initially explored with moderate enantioselectivity.

Palladium-Catalyzed Carbonylations: Application in Complex Natural Product Total Synthesis and Recent Developments

Carbon monoxide is a cheap and abundant C1 building block that can be readily incorporated into organic molecules to rapidly build structural complexity. In this Perspective, we outline several recent (since 2015) examples of palladium-catalyzed carbonylations in streamlining complex natural product total synthesis and highlight the strategic importance of these carbonylation reactions in the corresponding synthesis. The selected examples include spinosyn A, callyspongiolide, perseanol, schizozygane alkaloids, cephanolides, and bisdehydroneostemoninine and related stemona alkaloids. We also provide our perspective about the recent advancements and future developments of palladium-catalyzed carbonylations.

Pd-Catalyzed Asymmetric 5-exo-trig Cyclization/Cyclopropanation/Carbonylation of 1,6-Enynes for the Construction of Chiral 3-Azabicyclo[3.1.0]hexanes

We herein disclose a mild and efficient access to chiral 3-azabicyclo[3.1.0]hexanes via a Pd-catalyzed asymmetric 5-exo-trig cyclization/cyclopropanation/carbonylation of 1,6-enynes. Various nucleophiles, such as alcohols, phenols, amines and water, are well compatible with the reaction system. This reaction forms three C-C bonds, two rings, two adjacent quaternary carbon stereocenters as well as one C-O/C-N bond with excellent regio- and enantioselectivities. The products could be further functionalized to generate a library of 3-azabicyclo[3.1.0]hexane frameworks.

Palladium-Catalyzed Reductive Double Carbonylation of Nitroarenes with Aryl Halides Using Mo(CO)6 as a Reductant and Carbonyl Source

A new palladium-catalyzed reductive double carbonylation of nitroarenes with aryl halides for the synthesis of benzoxazin-4-ones has been reported. The key to success was the use of Mo(CO)₆ as a reductant and bench-stable solid carbonyl sources. Various aryl iodides, bromides, and trifluoromethanesulfonates are suitable reaction partners and produce corresponding benzoxazin-4-one derivatives in moderate to good yields. Preliminary mechanistic studies indicate that nitrosoarene was first generated as the key intermediate through nitro reduction. Remarkably, this method avoids the use of toxic CO gas and is further applied to the late-stage modification of estrone.

Asymmetric Cascade Carbonylation/Annulation of Benzyl Bromides, CO, and Vinyl Benzoxazinanones Enabled by Pd/Chiral Lewis-Base Relay Catalysis

A highly enantioselective cascade carbonylation/annulation of benzyl bromides, CO, and vinyl benzoxazinanones under mild conditions has been established by Pd/chiral Lewis base relay catalysis, providing an efficient method to assemble chiral quinolinones from readily available starting materials in good yields with excellent diastereo- and enantioselectivities. The palladium catalyst plays two roles in this reaction, enabling both the carbonylation process and the generation of the zwitterionic π-allyl palladium intermediate.

Pd-Catalyzed Enantioselective Hydroamidocarbonylation of α-Substituted Acrylamides to Chiral Succinimides

With the aid of an innate amide group, an intramolecular Pd-catalyzed enantioselective hydroamidocarbonylation reaction of α-substituted acrylamides was developed, and a series of chiral 2-substituted succinimides were obtained in moderate to high yields and enantioselectivities. The generality of this approach was demonstrated by the carbonylation of both aryl- and alkyl-substituted acrylamides containing numerous functional groups.

Progress on transition metal catalyzed asymmetric hydroesterification, hydrocarboxylation, and hydroamidation reactions of olefins

Hydrocarboxylation, hydroesterification, and hydroamidation of olefins are fundamental transformations in organic synthesis. Asymmetric processes for these transformations provide an effective and straightforward approach to optically active carboxylic acids and their derivatives, which are highly useful compounds in pharmaceuticals, materials, fine chemicals, etc. This review provides a brief summary of the development of asymmetric hydroesterification, hydrocarboxylation, and hydroamidation with CO and its surrogates.

Oxidative C-H/N-H Carbonylation of Benzamide by Nickel Catalysis with CO as the Carbonyl Source

An efficient and direct carbonylation of aminoquinoline benzamides has been developed using abundant and inexpensive Ni(OAc)₂·4H₂O as the catalyst and carbon monoxide as a cost-efficient C1 building block. This process features good functional-group tolerance and can be conducted on gram scale. The directing group can be easily removed under mild conditions.

Photoredox/Iron Dual-Catalyzed Insertion of Acyl Nitrenes into C-H Bonds

In this work, the use of N-acyloxybenzamides as efficient acyl nitrene precursors under photoredox/iron dual catalysis is reported. The resulting acyl nitrenes could be captured by various types of C-H bonds and S- or P-containing molecules. Mechanism investigations suggested that the formation of the acyl nitrene from the N-acyloxybenzamide occurs by a photoredox process, and it is believed that in this redox process oxidative N-H bond cleavage of the N-acyloxybenzamide occurs prior to reductive N-O bond cleavage of the N-acyloxybenzamide.

Assembling Chiral Center of Heterocycles by Palladium-catalyzed Asymmetric Hydrocarbonylation

The strategy of embedding coordinative functional group into the starting material is frequently employed to enhance reactivity and enantioselectivity in various asymmetric catalytic reactions other than enantioselective hydrocarbonylation. Recent progress in palladium-catalyzed asymmetric hydrocarbonylation with this strategy for the synthesis of chiral heterocycles was highlighted. The merits of the innate coordinative functional group not only enhance the reactivity and boost the multiple selectivity, but also facilitates the synthesis of chiral heterocycles.

Palladium-Catalyzed Intermolecular Carbonylation-Based Difunctionalization of Alkenes

The palladium(II)-catalyzed carbonylation of alkenes presents one of most efficient methods for the synthesis of alkyl-substituted carbonyls and has received much attention. In this Account, we summarize our recent studies on the palladium-catalyzed intermolecular carbonylation-based 1,2-difunctionalization of alkenes, in which two strategies were involved: (1) a cooperative strategy involves the sequential iodine(III)-mediated alkene activation and palladium-catalyzed carbonylation, leading to the intermolecular β-oxy-, fluoro-, and azidocarbonylation of alkenes; (2) the classic strategy initiated by intermolecular nucleopalladation and carbonylation, including the asymmetric oxycarbonylation of alkenes. These methods provide a series of efficient approaches to synthesize β-functionalized aliphatic carboxylic derivatives.

1 Introduction

2 A Cooperative Strategy Involving Iodine(III)-Mediated Alkene Activation and Palladium-Catalyzed Carbonylation

2.1 Intermolecular Oxycarbonylation of Alkenes

2.2 Intermolecular Fluorocarbonylation of Alkenes

2.3 Intermolecular Azidocarbonylation of Alkenes

3 Intermolecular Aminocarbonylation of Alkenes Initiated by Aminopalladation

4 Intermolecular Arylcarbonylation of Alkenes Initiated by Arylpalladation

5 Intermolecular Enantioselective Oxycarbonylation of Alkenes Initiated by Oxypalladation

6 Conclusion

Recent Advances in Visible-Light-Mediated Amide Synthesis

Visible-light photoredox catalysis has attracted tremendous interest within the synthetic community. As such, the activation mode potentially provides a more sustainable and efficient platform for the activation of organic molecules, enabling the invention of many controlled radical-involved reactions under mild conditions. In this context, amide synthesis via the strategy of photoredox catalysis has received growing interest due to the ubiquitous presence of this structural motif in numerous natural products, pharmaceuticals and functionalized materials. Employing this strategy, a wide variety of amides can be prepared effectively from halides, arenes and even alkanes under irradiation of visible light. These methods provide a robust alternative to well-established strategies for amide synthesis that involve condensation between a carboxylic acid and amine mediated by a stoichiometric activating agent. In this review, the representative progresses made on the synthesis of amides through visible light-mediated radical reactions are summarized.

Palladium-catalyzed tandem Heck/carbonylation/aminocarbonylation en route to chiral heterocyclic α-ketoamides

An unprecedented tandem carbonylation/aminocarbonylation triggered by palladium-catalyzed enantioselective Heck-type exocyclopalladation delivering chiral heterocyclic α-ketoamides has been developed.