Diethylzinc-promoted carboxylation of aryl/alkenyl boronic acids with CO2

The carboxylation of aryl and alkenyl boronic acids with CO2 is rarely studied and only achieved using copper salts as the catalyst in the presence of a strong base. Herein, we report a diethylzinc-promoted carboxylation of aryl or alkenyl boronic acids with carbon dioxide. The reaction does not require a transition-metal catalyst, and has simple and mild conditions and a broad substrate scope.

Cu-catalyzed carboxylation of organoboronic acid pinacol esters with CO2

Chemical fixation of CO2 has received much attention. In particular, catalytic C-C bond formation with CO2 giving carboxylic acids is of great significance. Among the CO2 fixation methods, multiple carboxylation is one of the challenging subjects. Here we investigated the Cu-catalyzed carboxylation of a variety of boronic acid pinacol esters (C(sp2)-, C(sp3)-, and C(sp)-B compounds) with CO2, which efficiently provided the corresponding products, including aryl, alkenyl, alkyl, and alkynyl carboxylic acids. This carboxylation was also applicable to multiple CO2 fixation giving di- and tri-carboxylic acids under robust reaction conditions (totally 29 examples).

Palladium-Catalyzed Carbonylation of Aryl Bromides with Carbon Dioxide To Access Aryl Carboxylic Acids under Mild Conditions

A palladium-catalyzed direct carbonylation of aryl bromides with carbon dioxide as the carbonyl source has been developed by using Pd(dba)₂/DPEPhos as the catalyst under mild reaction conditions, providing an efficient route to a variety of aryl carboxylic acids in moderate to high yields. The methods have many advantages such as the use of a simple palladium catalyst system, wide substrate scope, good functional group tolerance, high yields, and easy scalability.

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

Transmetalation of boronic acids and their derivatives: mechanistic elucidation and relevance to catalysis

The Suzuki-Miyaura reaction (the cross-coupling reaction of boronic acids with organic halides catalysed by Pd complexes) has been recognised as a useful synthetic organic reaction that forms a C(sp²)-C(sp²) bond. The catalytic cycle of the reaction involves the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. It migrates the aryl and alkenyl groups of boronic acid to Pd and produces a Pd-C bond. Many studies have investigated the mechanism of transmetalation. They elucidated the mechanism of the organometallic reaction and its role as a fundamental step in catalytic reactions. This perspective reviews studies on the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. Emphasis was laid on the structures and chemical properties of the intermediate Pd complexes and the effects of OH^- on the pathways of the catalytic Suzuki-Miyaura reaction. The reactions of arylboronic acids with Rh(I)-OH complexes were investigated, which are relevant to the mechanism of Rh-catalysed addition of aryl boronic acids to enones and aldehydes. Recent studies on the transmetalation of boronic acids with other late transition metals such as Fe(II), Co(I), Pt(II), Au(III), and Au(I) are presented with the related catalytic reactions and their utilisation in the synthesis of aromatic molecules and π-conjugated materials.

Carboxylation of sodium arylsulfinates with CO2 over mesoporous K-Cu-20TiO2

A mesoporous ternary metal oxide (K-Cu-20TiO₂) from a simple sol–gel method was prepared to catalyze heterogeneously the carboxylation reaction of various sodium arylsulfinates under atmospheric carbon dioxide. The catalyst showed excellent selectivity and good functional group tolerance to carboxylation recycle. The oxidation state of active copper(i) by characterization using FTIR, XRD, TG, XPS and TEM techniques proved to be efficacious to conduct atom economical reactions.

A mesoporous ternary metal oxide (K-Cu-20TiO₂) from a simple sol–gel method was prepared to catalyze heterogeneously the carboxylation reaction of various sodium arylsulfinates under atmospheric carbon dioxide.

Efficient Syntheses of Biobased Terephthalic Acid, p-Toluic Acid, and p-Methylacetophenone via One-Pot Catalytic Aerobic Oxidation of Monoterpene Derived Bio-p-cymene

An efficient elevated-pressure catalytic oxidative process (2.5 mol % Co(NO₃)₂, 2.5 mol % MnBr₂, air (30 bar), 125 °C, acetic acid, 6 h) has been developed to oxidize p-cymene into crystalline white terephthalic acid (TA) in ∼70% yield. Use of this mixed Co²⁺/Mn²⁺ catalytic system is key to obtaining high 70% yields of TA at relatively low reaction temperatures (125 °C) in short reaction times (6 h), which is likely to be due to the synergistic action of bromine and nitrate radicals in the oxidative process. Recycling studies have demonstrated that the mixed metal catalysts present in recovered mother liquors could be recycled three times in successive p-cymene oxidation reactions with no loss in catalytic activity or TA yield. Partial oxidation of p-cymene to give p-methylacetophenone (p-MA) in 55-60% yield can be achieved using a mixed CoBr₂/Mn(OAc)₂ catalytic system under 1 atm air for 24 h, while use of Co(NO₃)₂/MnBr₂ under 1 atm O₂ for 24 h gave p-toluic acid in 55-60% yield. Therefore, access to these simple catalytic aerobic conditions enables multiple biorenewable bulk terpene feedstocks (e.g., crude sulfate turpentine, turpentine, cineole, and limonene) to be converted into synthetically useful bio-p-MA, bio-p-toluic acid, and bio-TA (and hence bio-polyethylene terephthalate) as part of a terpene based biorefinery.

Dissecting transmetalation reactions at the molecular level: C-B versus F-B bond activation in phenyltrifluoroborate silver complexes

The gas-phase unimolecular reactions of the silver(i) complex [Ag(PhBF₃)₂]^-, formed via electrospray ionisation mass spectrometry of solutions containing the phenyltrifluoroborate salt and AgNO₃, are examined. Upon collision induced dissociation (CID) three major reaction channels were observed for [Ag(PhBF₃)₂]^-: Ph^- group transfer via a transmetalation reaction to yield [PhAg(PhBF₃)]^-; F^- transfer to produce [FAg(PhBF₃)]^-; and release of PhBF₃^-. The anionic silver product complexes of these reactions, [LAg(PhBF₃)]^- (where L = Ph and F), were then mass-selected and subjected to a further stage of CID. [PhAg(PhBF₃)]^- undergoes a Ph^- group transfer via transmetalation to yield [Ph₂Ag]^- with loss of BF₃. [FAg(PhBF₃)]^- solely fragments via loss of BF₄^-, a reaction that involves Ph^- group transfer from B to Ag in conjunction with F^- transfer from Ag to B. Density functional theory (DFT) calculations on the various competing pathways reveal that: (i) the overall endothermicities govern the experimentally observed product ion abundances; (ii) the Ph^- group and F^- transfer reactions proceed via late transition states; and (iii) formation of BF₄^- from [FAg(PhBF₃)]^- is a multistep reaction in which Ph^- group transfer from B to Ag proceeds first to produce a [FAgPh(BF₃)]^- complex in which the BF₃ moiety is initially weakly bound to the ipso-carbon of the phenyl group and then migrates across the linear [FAgPh]^- moiety from C to Ag to F yielding [PhAg(BF₄)]^-, which can then dissociate via loss of PhAg.

Formal C-H Carboxylation of Unactivated Arenes

A formal C-H carboxylation of unactivated arenes using CO2 in green solvents is described. The present strategy combines a sterically controlled Ir-catalyzed C-H borylation followed by a Cu-catalyzed carboxylation of the in situ generated organoboronates. The reaction is highly regioselective for the C-H carboxylation of 1,3-disubstituted and 1,2,3-trisubstituted benzenes, 1,2- or 1,4-symmetrically substituted benzenes, fluorinated benzenes and different heterocycles. The developed methodology was applied to the late-stage C-H carboxylation of commercial drugs and ligands.

Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions

A range of hitherto unexplored biomass-derived chemicals have been evaluated as new sustainable solvents for a large variety of CO2 -based carboxylation reactions. Known biomass-derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, such as Cu-catalyzed carboxylation of organoboranes and organoboronates, metal-catalyzed hydrocarboxylation, borocarboxylation, and other related reactions. For many of these reactions, the use of biosolvents provides comparable or better yields than the commonly used solvents. The best biosolvents identified are the so far unexplored candidates isosorbide dimethyl ether, acetaldehyde diethyl acetal, rose oxide, and eucalyptol, alongside the known biosolvent 2-methyltetrahydrofuran. This strategy was used for the synthesis of the commercial drugs Fenoprofen and Flurbiprofen.

Reductive Coupling of Carbon Dioxide and an Aldehyde Mediated by a Copper(I) Complex toward the Synthesis of α-Hydroxycarboxylic Acids

Copper-mediated reductive coupling between CO₂ and an aldehyde to form α-hydroxycarboxylic acid was achieved using silylborane as a reductant. CO₂ cleanly inserted into a copper-carbon bond that was formed by the reaction between a silylcopper-NHC complex and an aldehyde. A series of reactions that regenerate the silylcopper complex were developed for the synthesis of an α-hydroxycarboxylic acid. After repeating each step iteratively for two cycles, 0.62 equiv of α-hydroxycarboxylic acid based on the copper complex was obtained.

One-Pot Synthesis of α,β-Unsaturated γ-Lactones and Lactams via a Sequential trans-Hydroalumination and Catalytic Carboxylation of Propargyl Alcohols and Amines with Carbon Dioxide

A one-pot, sequential process that combines a trans-selective hydroalumination of propargyl alcohols and amines with a copper- or silver-catalyzed carboxylation reaction using carbon dioxide, followed by an acid-mediated intramolecular condensation step, led to the formation of a wide range of α,β-unsaturated γ-butyrolactones and lactams.

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C-H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.

Cu-Catalysed carboxylation of aryl boronic acids with CO2

A copper/N-heterocyclic carbene (NHC) catalysed carboxylation of aryl boronic acids under one atmospheric pressure of CO₂ has been developed.

Cobalt-Catalyzed Oxygenation/Dearomatization of Furans

The dearomatization of aromatic compounds using cobalt(II) acetylacetonate with triplet oxygen and triethylsilane converts furans, benzofurans, pyrroles, and thiophenes to a variety of products, including lactones, silyl peroxides, and ketones.

Palladium-catalyzed oxidative coupling of arylboronic acid with isocyanide to form aromatic carboxylic acids

A valuable palladium-catalyzed oxidative coupling of aryl- and alkenyl borides with isocyanide for the synthesis of corresponding carboxylic acids has been developed. With wide substrate scopes and good functional group tolerance, this reaction offers corresponding carboxylic acids in moderate to excellent yields.

tert-Butyl Nitrite-Mediated Synthesis of N-Nitrosoamides, Carboxylic Acids, Benzocoumarins, and Isocoumarins from Amides

This work reports tert-butyl nitrite (TBN) as a multitask reagent for (1) the controlled synthesis of N-nitrosoamide from N-alkyl amides, (2) hydrolysis of N-methoxyamides to carboxylic acids, (3) metal- and oxidant-free benzocoumarin synthesis from ortho-aryl-N-methoxyamides via N-H, C-N, and C-H bond activation, and (4) isocoumarin synthesis using Ru(II)/PEG as a recyclable catalytic system via ortho-C-H activation and TBN as an oxygen source. The sequential functional group interconversion of amide to acid has also been examined using IR spectroscopic analysis. Additionally, this methodology is highly advantageous due to short reaction time, gram scale synthesis, and broad substrate scope.

Synthesis of Carboxylic Acids and Esters from CO2

The achievements in the synthesis of carboxylic acids and esters from CO₂ have been summarized and discussed.

Silver-catalyzed carboxylation

The recent studies of the silver-catalyzed carboxylation reactions using carbon dioxide are described.

Double carboxylation of o-alkynyl acetophenone with carbon dioxide

A copper-catalyzed double carboxylation of o-alkynyl acetophenone using carbon dioxide via a carboxylation/intramolecular cyclization/second carboxylation sequence to afford 1(3H)-isobenzofuranylidene dicarboxylic esters in good yields is developed.

Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Alkylative carboxylation of ynamides with CO2 and dialkylzinc reagents using a N-heterocyclic carbene (NHC)-copper catalyst has been developed. A variety of ynamides, both cyclic and acyclic, undergo this transformation under mild conditions to afford the corresponding α,β-unsaturated carboxylic acids, which contain the α,β-dehydroamino acid skeleton. The present alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents with the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2 . Dialkylzinc reagents bearing a β-hydrogen atom such as Et2 Zn and Bu2 Zn still afford the alkylated products despite the potential for β-hydride elimination. This protocol would be a desirable method for the synthesis of highly substituted α,β- dehydroamino acid derivatives due to its high regio- and stereoselectivity, simple one-pot procedure, and its use of CO2 as a starting material.

Synthesis of oxazolidine-2,4-diones by a tandem phosphorus-mediated carboxylative condensation–cyclization reaction using atmospheric carbon dioxide

A novel access to oxazolidine-2,4-diones using atmospheric CO₂ and readily available substrates under mild and transition-metal-free conditions is developed.