Functional Group Interconversion: Decarbonylative Borylation of Esters for the Synthesis of Organoboronates

Divergent Transformations of Aromatic Esters: Decarbonylative Coupling, Ester Dance, Aryl Exchange, and Deoxygenative Coupling

ConspectusAromatic esters are cost-effective, versatile, and commonly used scaffolds that are readily synthesized or encountered as synthetic intermediates. While most conventional reactions involving these esters are nucleophilic acyl substitutions or 1,2-nucleophilic additions─where a nucleophile attacks the carbonyl group, decarbonylative transformations offer an alternative pathway by using the carbonyl group as a leaving group. This transition-metal-catalyzed process typically begins with oxidative addition of the C(acyl)-O bond to the metal. Subsequently, the reaction involves the migration of CO to the metal center, the reaction with a nucleophile, and reductive elimination to yield the final product. Pioneering work by Yamamoto on nickel complexes and the development of decarbonylative reactions (such as Mizoroki-Heck-type olefination) using aromatic carboxylic anhydrides catalyzed by palladium were conducted by de Vries and Stephan. Furthermore, reports have surfaced of decarbonylative hydrogenation of pyridyl methyl esters by Murai using ruthenium catalysts as well as Mizoroki-Heck-type reactions of nitro phenyl esters by Gooßen under palladium catalysis. Our group has been at the forefront of developing decarbonylative C-H arylations of phenyl esters with 1,3-azoles and aryl boronic acids using nickel catalysts. The key to this reaction is the use of phenyl esters, which are easy to synthesize, stabilize, and handle, allowing oxidative addition of the C(acyl)-O bond; nickel, which facilitates oxidative addition of the C(acyl)-O bond; and suitable bidentate phosphine ligands that can stabilize the intermediate. By modification of the nucleophiles, esters have been effectively utilized as electrophiles in cross-coupling reactions, encouraging the development of these nucleophiles among researchers. This Account summarizes our advancements in nucleophile development for decarbonylative coupling reactions, particularly highlighting the utilization of aromatic esters in diverse reactions such as alkenylation, intramolecular etherification, α-arylation of ketones, C-H arylation, methylation, and intramolecular C-H arylation for dibenzofuran synthesis, along with cyanation and reductive coupling. We also delve into reaction types that are distinct from typical decarbonylative reactions, including ester dance reactions, aromatic ring exchanges, and deoxygenative transformations, by focusing on the oxidative addition of the C(acyl)-O bond of the aromatic esters to the metal complex. For example, the ester dance reaction is hypothesized to undergo 1,2-translocation starting with oxidative addition to a palladium complex, leading to a sequence of ortho-deprotonation/decarbonylation, followed by protonation, carbonylation, and reductive elimination. The aromatic exchange reaction likely involves oxidative addition of complexes of different aryl electrophiles with a nickel complex. In deoxygenative coupling, an oxidative addition complex with palladium engages with a nucleophile, forming an acyl intermediate that undergoes reductive elimination in the presence of an appropriate reducing agent. These methodologies are poised to captivate the interest of synthetic chemists by offering unconventional and emerging approaches for transforming aromatic esters. Moreover, we demonstrated the potential to transform readily available basic chemicals into new compounds through organic synthesis.

Decarbonylative borylation of aryl anhydrides via rhodium catalysis

Decarbonylative borylation of aryl anhydrides by rhodium catalysis has been reported. A base-free system with Rh(PPh3)3Cl as a catalyst enables the efficient synthesis of various arylboronate esters from readily available aryl anhydrides. The reaction involves the cleavage of C(O)-O bonds and the formation of C-B bonds. The experimental results demonstrated that compared with carboxylic acids, amides, and esters, anhydrides have higher reactivity in the decarbonylative borylation reaction under the current conditions. Furthermore, compared with the reported palladium-catalyzed borylation reaction of aryl anhydrides, the present rhodium-catalyzed method has the advantages of a shorter reaction time and a lower reaction temperature.

Formation of C(sp2)-C(sp3) Bonds Instead of Amide C-N Bonds from Carboxylic Acid and Amine Substrate Pools by Decarbonylative Cross-Electrophile Coupling

Carbon-heteroatom bonds, most often amide and ester bonds, are the standard method to link together two complex fragments because carboxylic acids, amines, and alcohols are ubiquitous and the reactions are reliable. However, C-N and C-O linkages are often a metabolic liability because they are prone to hydrolysis. While C(sp2)-C(sp3) linkages are preferable in many cases, methods to make them require different starting materials or are less functional-group-compatible. We show here a new, decarbonylative reaction that forms C(sp2)-C(sp3) bonds from the reaction of activated carboxylic acids (via 2-pyridyl esters) with activated alkyl groups derived from amines (via N-alkyl pyridinium salts) and alcohols (via alkyl halides). Key to this process is a remarkably fast, reversible oxidative addition/decarbonylation sequence enabled by pyridone and bipyridine ligands that, under reaction conditions that purge CO(g), lead to a selective reaction. The conditions are mild enough to allow coupling of more complex fragments, such as those used in drug development, and this is demonstrated in the coupling of a typical Proteolysis Targeting Chimera (PROTAC) anchor with common linkers via C-C linkages.

Nickel(0)-Catalyzed Decarbonylative Cross-Coupling of Aromatic Esters with Arylboronic Acids via Chelation Assistance

10-Arylbenzo[h]quinolines were synthesized by cross-coupling of ethyl benzo[h]quinoline-10-carboxylate with arylboronic acids via group-directed Ni(0) catalyzation. The catalytic system combining Ni(COD)₂ (10 mol %) with PCy₃ (20 mol %) and t-BuOK (3 equiv) was optimal for the above transformations. A series of arylboronic acids reacted with ethyl benzo[h]quinoline-10-carboxylates for the production of various substituted 10-phenyl[h]quinolines in moderate and good yields under optimized reaction conditions.

Catalysis with Diboron(4)/Pyridine: Application to the Broad-Scope [3 + 2] Cycloaddition of Cyclopropanes and Alkenes

In contrast to the extensive but non-recyclable use of tetraalkoxydiboron(4) compounds as stoichiometric reagents in diverse reactions, this article reports an atom-economical reaction using a commercial diboron(4) as the catalyst. The key to success was designing a catalytic cycle for radical [3 + 2] cycloaddition involving a pyridine cocatalyst to generate from the diboron(4) catalyst and reversibly mediate the transfer of boronyl radicals. In comparison with known [3 + 2] cycloaddition with transition metal-based catalysts, the current reaction features not only metal-free conditions, inexpensive and stable catalysts, and simple operation but also remarkably broadened substrate scope. In particular, previously unusable cyclopropyl ketones without an activating group and/or alkenes with 1,2-disubstitution and 1,1,2-trisubstitution patterns were successfully used for the first time. Consequently, challenging cyclopentane compounds with various levels of substitution (65 examples, 57 new products, up to six substituents at all five ring atoms) were readily prepared in generally high to excellent yield and diastereoselectivity. The reaction was also successfully applied in concise formal synthesis of an anti-obesity drug and building natural product-like complex bridged or spirocyclic compounds. Mechanistic experiments and computational investigation support the proposed radical relay catalysis featuring a pyridine-assisted boronyl radical catalyst. Overall, this work demonstrates the first approach to use tetraalkoxydiboron(4) compounds as catalysts and may lead to the development of new, green, and efficient transition metal-like boron-catalyzed organic reactions.

Decarboxylative Borylation and Cross-Coupling of (Hetero)aryl Acids Enabled by Copper Charge Transfer Catalysis

We report a copper-catalyzed strategy for arylboronic ester synthesis that exploits photoinduced ligand-to-metal charge transfer (LMCT) to convert (hetero)aryl acids into aryl radicals amenable to ambient-temperature borylation. This near-UV process occurs under mild conditions, requires no prefunctionalization of the native acid, and operates broadly across diverse aryl, heteroaryl, and pharmaceutical substrates. We also report a one-pot procedure for decarboxylative cross-coupling that merges catalytic LMCT borylation and palladium-catalyzed Suzuki-Miyaura arylation, vinylation, or alkylation with organobromides to access a range of value-added products. The utility of these protocols is highlighted through the development of a heteroselective double-decarboxylative C(sp²)-C(sp²) coupling sequence, pairing copper-catalyzed LMCT borylation and halogenation processes of two distinct acids (including pharmaceutical substrates) with subsequent Suzuki-Miyaura cross-coupling.

Ru(dppbsa)-catalyzed hydrodeoxygenation and reductive etherification of ketones and aldehydes

Ru(dppbsa)-catalyzed hydrodeoxygenation and reductive etherification of ketones and aldehydes were developed. The carbonyl substrates without β-CH functionality follow the hydrogenation-hydrogenolysis path, wherein the hydrogenolysis of the alkanol intermediates presents as...

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Palladium-Catalyzed Decarbonylative Borylation of Aryl Anhydrides

A palladium-catalyzed base-free decarbonylative borylation of aryl anhydrides has been developed. Catalyst system consisting of Pd(OAc)₂/dppb enables readily available aryl anhydrides to be employed as electrophiles for the synthesis of versatile arylboronate esters via O-C(O) bond activation and decarbonylation. This method is characterized by an excellent functional group tolerance and broad substrate scope, using bench stable aryl anhydrides as aryl electrophiles in C-B bond formation. Mechanistic studies and functionalization of late-stage pharmaceutical molecules are disclosed.

Ni-Catalyzed Borylation of Aryl Sulfoxides

A nickel/N-heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B2 (neop)2 (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron-deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni-catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4-(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans-[Ni(ICy)2 (4-CF3 -C6 H4 ){(SO)-4-MeO-C6 H4 }] 4. For complex 5, the isomer trans-[Ni(ICy)2 (C6 H5 )(OSC6 H5 )] 5-I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans-[Ni(ICy)2 (C6 H5 )(OSC6 H5 )] 5-I is in equilibrium with the S-bonded isomer trans-[Ni(ICy)2 (C6 H5 )(SOC6 H5 )] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2-TZVP-level of theory) and connected via a transition state trans-[Ni(ICy)2 (C6 H5 )(η2 -{SO}-C6 H5 )], which lies only 10.8 kcal/mol above 5.

Copper-Mediated Dichotomic Borylation of Alkyne Carbonates: Stereoselective Access to (E)-1,2-Diborylated 1,3-Dienes versus Traceless Monoborylation Affording α-Hydroxyallenes

A mild copper-mediated protocol has been developed for borylation of alkynyl cyclic carbonates. Depending on the nature of the borylating reaction partner, either stereoselective diborylation of the propargylic surrogate takes place, providing convenient access to (E)-1,2-borylated 1,3-dienes, or traceless monoborylation occurs, which leads to α-hydroxyallenes as the principal product. The dichotomy in this borylation protocol has been scrutinized by several control experiments, illustrating that a relatively small change in the diboron(4) reagent allows for competitive alcohol-assisted protodemetalation to forge an α-hydroxyallene product under ambient conditions.

Nickel-Catalyzed Directed Cross-Electrophile Coupling of Phenolic Esters with Alkyl Bromides

Herein, we demonstrate the successful use of robust phenolic esters as an electrophilic acyl source in the reaction with diverse primary and secondary unactivated alkyl bromides. The cleavage of the relatively inert C-O bond is facilitated by the neighboring coordinating hydroxyl or sulfonamide moiety. By circumventing the use of pregenerated organometallics, this method allows efficient preparation of a variety of o-hydroxyl and tosyl-protected o-amino aryl ketones with high compatibility with a wide range of functionalities.

Rh-Catalyzed Base-Free Decarbonylative Borylation of Twisted Amides

We report the rhodium-catalyzed base-free decarbonylative borylation of twisted amides. The synthesis of versatile arylboronate esters from aryl twisted amides is achieved via decarbonylative rhodium(I) catalysis and highly selective N-C(O) insertion. The method is notable for a very practical, additive-free Rh(I) catalyst system. The method shows broad functional group tolerance and excellent substrate scope, including site-selective decarbonylative borylation/Heck cross-coupling via divergent N-C/C-Br cleavage and late-stage pharmaceutical borylation.

Nickel(II)-Catalyzed Borylation of Alkenyl Methyl Ethers via C-O Bond Cleavage

A new protocol has been developed for the borylation of conjugated alkenyl methyl ethers using B₂Pin₂ via C-O bond cleavage catalyzed by Ni(II). In this cross-coupling reaction, both E/Z isomers of alkenyl ethers are converted into (E)-alkenyl boronic esters with good reactivity. This transformation exhibits high chemoselectivity in the presence of competitive C-O bonds such as aryl ether, ester, amide, and thioether groups, thus providing a new method for the construction of various alkenyl boronates.

Methodologies and Strategies for Selective Borylation of C-Het and C-C Bonds

Organoborons have emerged as versatile building blocks in organic synthesis to achieve molecular diversity and as carboxylic acid bioisosteres with broad applicability in drug discovery. Traditionally, these compounds are prepared by the substitution of Grignard/lithium reagents with electrophilic boron species and Brown hydroboration. Recent developments have provided new routes for the efficient preparation of organoborons by applying reactions using chemical feedstocks with leaving groups. As compared to the previous methods that used organic halides (I, Br, and Cl), the direct borylation of less reactive C-Het and C-C bonds has become highly important to get efficiency and functional-group compatibility. This Review aims to provide a comprehensive overview of this topic, including (1) C-F bond borylation, (2) C-O bond borylation, (3) C-S bond borylation, (4) C-N bond borylation, and (5) C-C bond borylation. Considerable attention is given to the strategies and mechanisms involved. We expect that this Review will inspire chemists to discover more efficient transformations to expand this field.

Mechanism and Scope of Nickel-Catalyzed Decarbonylative Borylation of Carboxylic Acid Fluorides

This Article describes the development of a base-free, nickel-catalyzed decarbonylative coupling of carboxylic acid fluorides with diboron reagents to selectively afford aryl boronate ester products. Detailed studies were conducted to assess the relative rates of direct transmetalation between aryl boronate esters and diboron reagents and a bisphosphine nickel(aryl)(fluoride) intermediate. These investigations revealed that diboron reagents undergo transmetalation with this Ni(aryl)(fluoride) intermediate at rates significantly faster than their aryl boronate ester congeners. Furthermore, the reactivity of both boron reagents toward transmetalation is enhanced with increasing electrophilicity of the boron center. These mechanistic insights were leveraged to develop a catalytic decarbonylative borylation of acid fluorides that proved applicable to a variety of (hetero)aryl carboxylic acid fluorides as well as diverse diboron reagents. The acid fluorides can be generated in situ directly from carboxylic acids. Furthermore, the mechanistic studies directed the identification of various air-stable Ni pre-catalysts for this transformation.

Redox-Neutral Decarbonylative Cross-Couplings Coming of Age

Major progress has recently been made in the challenging redox-neutral decarbonylative cross-coupling of carboxylic acids. For example, the use of acid fluorides as effective cross-coupling partners has been found to enable control of the decarbonylation selectivity and facilitates challenging Pd⁰ -catalyzed nucleophilic trifluoromethylation and exogenous base-free Suzuki cross-coupling reactions. In another recent advance, the use of acid chlorides in room temperature difluoromethylation and direct decarbonylative cross-coupling of carboxylic acids allows these classical substrates to be used as aryl electrophiles in cross-coupling reactions. Further challenges that are yet to be addressed in redox-neutral decarbonylative cross-couplings are also briefly summarized.

Heterogeneous Suzuki-Miyaura coupling of heteroaryl ester via chemoselective C(acyl)-O bond activation

A site-selective supported palladium nanoparticle catalyzed Suzuki-Miyaura cross-coupling reaction with heteroaryl esters and arylboronic acids as coupling partners was developed. This methodology provides a heterogeneous catalytic route for aryl ketone formation via C(acyl)-O bond activation of esters by successful suppression of the undesired decarbonylation phenomenon. The catalyst can be reused and shows high activity after eight cycles. The XPS analysis of the catalyst before and after the reaction suggested that the reaction might be performed via a Pd0/PdII catalytic cycle that began with Pd0.

Direct Transformation of Aryl 2-Pyridyl Esters to Secondary Benzylic Alcohols by Nickel Relay Catalysis

A direct transformation of aryl esters to secondary benzylic alcohols via tandem Ni-catalyzed cross-coupling reactions of aromatic 2-pyridyl esters with alkyl zinc reagents and carbonyl group reduction by Ni-H species is achieved. Preliminary mechanistic studies reveal that the Ni-H species is generated in situ via β-hydride elimination of the Negishi reagents. The reaction is catalyzed by bench-stable nickel salts under mild conditions with wide functional group tolerance.

Decarbonylative Borylation of Amides by Palladium Catalysis

The development of transition-metal-catalyzed borylation reactions is of significant importance for the fields of organic synthesis and medicinal chemistry because of the versatility of organoboron functional groups. Herein, we report the direct decarbonylative borylation of amides by highly selective carbon-nitrogen bond cleavage by palladium catalysis. The approach capitalizes on the ground-state destabilization of the amide bond in N-acyl glutarimides to achieve Pd-catalyzed insertion into the amide N-C bond and decarbonylation (deamidation). Mechanistic studies and the utility of this methodology in orthogonal sequential cross-couplings of robust, bench-stable amides are reported.

Recent advances in the borylative transformation of carbonyl and carboxyl compounds

The recent advances in the borylative transformation of carbonyl and carboxyl compounds are summarized.

Nickel-catalyzed exo-selective hydroacylation/Suzuki cross-coupling reaction

The first nickel-catalyzed intramolecular hydroacylation/Suzuki cross coupling cascade of o-allylbenzaldehydes with a broad range of phenylboronic acid neopentyl glycol esters has been developed.

Cooperation between an alcoholic proton and boryl species in the catalytic gem-hydrodiborylation of carboxylic esters to access 1,1-diborylalkanes

Cooperation between an alcoholic proton and boryl species in the selective gem-hydrodiborylation of carboxylic esters is described.

Ligation state of nickel during C-O bond activation with monodentate phosphines

The oxidative addition of phenolic electrophiles at Ni(0) in the presence of monodentate phosphine ligands was studied with both dispersion-free and dispersion-containing DFT methods. With the popular bulky ligand PCy3, consideration of dispersion has a striking effect on the predicted ligation state of nickel during oxidative addition of aryl sulfamates. Dispersioncontaining methods such as M06L indicate a clear preference for a bis-phosphine ligated transition state (TS), while dispersion free methods like B3LYP strongly favor a monophosphine ligated TS. This discrepancy in predicted ligation state is also found with small phosphines (PMe3) in combination with some aryl electrophiles (carbamates, acetates, pivalates, chlorides), but a bis-PMe3-ligated TS is predicted regardless of dispersion for other electrophiles (sulfamates, mesylates, tosylates). DFT calculations that include dispersion also offer a possible explanation for the observed poor efficacy of P t Bu3 as a ligand in Ni-catalyzed cross-coupling reactions.

Decarbonylative Cross-Couplings: Nickel Catalyzed Functional Group Interconversion Strategies for the Construction of Complex Organic Molecules

The utilization of carboxylic acid esters as electrophiles in metal-catalyzed cross-coupling reactions is increasingly popular, as environmentally friendly and readily available ester derivatives can be powerful alternatives to the commonly used organohalides. However, key challenges associated with the use of these chemicals remain to be addressed, including the stability of ester substrates and the high energy barrier associated with their oxidative addition to low-valent metal species. Due to recent developments in nickel catalysis that make it easier to perform oxidative additions, chemists have become interested in applying less reactive electrophiles as coupling counterparts in nickel-catalyzed transformations. Hence, our group and others have independently investigated various ester group substitutions and functionalizations enabled by nickel catalysis. Such methods are of great interest as they enable the exchange of ester groups, which can be used as directing groups in metal-catalyzed C-H functionalizations prior to their replacement. Here, we summarize our recent efforts toward the development of nickel-catalyzed decarbonylative cross-coupling reactions of carboxylic esters. Achievements accomplished by other groups in this area are also included. To this day, a number of new transformations have been successfully developed, including decarbonylative arylations, alkylations, cyanations, silylations, borylations, aminations, thioetherifications, stannylations, and hydrogenolysis reactions. These transformations proceed via a nickel-catalyzed decarbonylative pathway and have shown a high degree of reactivity and chemoselectivity, as well as several other unique advantages in terms of substrate availability, due to the use of esters as coupling partners. Although the mechanisms of these reactions have not yet been fully understood, chemists have already provided some important insights. For example, Yamamoto explored the stoichiometric nickel-mediated decarbonylation process of esters and proposed a reaction mechanism involving a C(acyl)-O bond cleavage and a CO extrusion. Key nickel intermediates were isolated and characterized by Shi and co-workers, supporting the assumption of a nickel/ N-heterocyclic carbene-promoted C(acyl)-O bond activation and functionalization. Our combined experimental and computational study of a ligand-controlled chemoselective nickel-catalyzed cross-coupling of aromatic esters with alkylboron reagents provided further insight into the reaction mechanism. We demonstrated that nickel complexes with bidentate ligands favor the C(aryl)-C bond cleavage in the oxidative addition step, resulting in decarbonylative alkylations, while nickel complexes with monodentate phosphorus ligands promote the activation of the C(acyl)-O bond, leading to the production of ketone products. Although more detailed mechanistic investigations need to be undertaken, the successful development of decarbonylative cross-coupling reactions can serve as a solid foundation for future studies. We believe that this type of decarbonylative cross-coupling reactions will be of significant value, in particularly in combination with the retrosynthetic analysis and synthesis of natural products and biologically active molecules. Thus, the presented ester substitution methods will pave the way for successful applications in the construction of complex frameworks by late-stage modification and functionalization of carboxylic acid derivatives.

Transition-Metal-Catalyzed Decarbonylative Coupling Reactions: Concepts, Classifications, and Applications

Transition metal-catalyzed decarbonylative coupling reactions have emerged as a powerful alternative to conventional cross-coupling protocols due to the advantages associated with the use of carbonyl-containing functionalities as coupling electrophiles instead of commonly used organohalides or sulfates. A wide variety of novel transformations based on this concept have been successfully achieved, including decarbonylative carbon-carbon and carbon-heteroatom bond forming reactions. In this Review, we summarize the recent progress in this field and present a comprehensive overview of metal-catalyzed decarbonylative coupling reactions with carbonyl derivatives.

Reductive Cleavage of Aromatic and Heteroaromatic Ester Functions via Copper-Catalyzed Proto-Decarbomethoxylation

An unprecedented catalytic reductive cleavage of aromatic and heteroaromatic methyl ester functions was successfully achieved with a cheap, nontoxic, and air-stable Cu(OAc)₂ catalyst. This reaction is fast, features good functional group tolerance, does not require inert atmosphere or anhydrous solvent, and can be scaled up to 1 g. Moreover, carboxylic acids and t-butyl esters also reacted smoothly under these conditions.

Cross-coupling of aromatic esters and amides

Catalytic cross-coupling reactions of aromatic esters and amides have recently gained considerable attention from synthetic chemists as de novo and efficient synthetic methods to form C-C and C-heteroatom bonds. Esters and amides can be used as diversifiable groups in metal-catalyzed cross-coupling: in a decarbonylative manner, they can be utilized as leaving groups, whereas in a non-decarbonylative manner, they can form ketone derivatives. In this review, recent advances of this research topic are discussed.

Ligand-Controlled Chemoselective C(acyl)-O Bond vs C(aryl)-C Bond Activation of Aromatic Esters in Nickel Catalyzed C(sp2)-C(sp3) Cross-Couplings

A ligand-controlled and site-selective nickel catalyzed Suzuki-Miyaura cross-coupling reaction with aromatic esters and alkyl organoboron reagents as coupling partners was developed. This methodology provides a facile route for C(sp²)-C(sp³) bond formation in a straightforward fashion by successful suppression of the undesired β-hydride elimination process. By simply switching the phosphorus ligand, the ester substrates are converted into the alkylated arenes and ketone products, respectively. The utility of this newly developed protocol was demonstrated by its wide substrate scope, broad functional group tolerance and application in the synthesis of key intermediates for the synthesis of bioactive compounds. DFT studies on the oxidative addition step helped rationalizing this intriguing reaction chemoselectivity: whereas nickel complexes with bidentate ligands favor the C(aryl)-C bond cleavage in the oxidative addition step leading to the alkylated product via a decarbonylative process, nickel complexes with monodentate phosphorus ligands favor activation of the C(acyl)-O bond, which later generates the ketone product.