Synthesis of Carboxylic Acids and Derivatives Using CO2 as Carboxylative Reagent

Carbon dioxide based methodologies for the synthesis of fine chemicals

Rapid environmental changes triggered by the increase in the concentration of heat-absorbing gases such as CO2 in the atmosphere have become a major cause of concern. One of the ways to counter this growing threat will be to efficiently convert atmospheric CO2 into value-added products via the development of efficient transition-metal-catalyzed processes. Conversion of CO2 into bulk products such as CH3OH and methane as well as its incorporation into commercial polyurethane synthesis has been achieved and reviewed extensively. However, the efficient transformation of CO2 into fine chemicals and value-added chemicals has many fold advantages. Recent years have seen a rapid rise in the number of metal-mediated protocols to achieve this goal of converting CO2 into fine chemicals. These are essential developments given the requirement of several commodities and fine chemicals in various industrial processes and the utilization of atmospheric CO2 will help provide a sustainable solution to the current environmental problems. Accordingly, we present here a comprehensive compilation of catalytic processes, involving CO2 as the C1 source for reacting with substrates such as alkanes, alkenes, alkynes, amines, acid chlorides, alcohols, allyl boronates, alkenyl triflates, and many others to provide easy access to a wide variety of useful molecules. Such a technology would certainly prove to be beneficial in solving the problems associated with the environmental accumulation of CO2.

ZnO nanoparticles supported on dendritic fibrous nanosilica as efficient catalysts for the one-pot synthesis of quinazoline-2,4(1H,3H)-diones

The transmutation of waste into valuable materials has a special place in green chemistry. Herein, we report the preparation of quinazoline-2,4(1H,3H)-diones from 2-iodoaniline, isocyanides, and carbon dioxide in the presence of ZnO NPs stably placed on the surface of dendritic fibrous nanosilica by cellulose (DFNS/cellulose-ZnO) as a catalyst. This is a great economic strategy to create three bonds in a one-pot multicomponent reaction step employing functional groups. To prepare the catalyst, the dendritic fibrous nanosilica surface was first activated using cellulose as a substrate to support ZnO NPs. Cellulose acts as a stabilizing and reducing agent for the ZnO nanocatalyst and eliminates the need for a reducing agent. The structure of the prepared DFNS/cellulose-ZnO was examined by various methods, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). The largest amount of quinazoline-2,4(1H,3H)-diones was obtained under ideal situations in the presence of 5 mg of DFNS/cellulose-ZnO under carbon dioxide (1 atm) utilizing a balloon set at 70 °C for 3 hours. The substance was reused for ten consecutive runs and the quinazoline-2,4(1H,3H)-dione content was more than 92% each time. This indicates the potential for application in the green and economic production of quinazoline-2,4(1H,3H)-diones, especially from low-cost feedstocks.

The transmutation of waste into valuable materials has a special place in green chemistry.

CO2 = CO + [O]: recent advances in carbonylation of C–H bonds with CO2

Carbon dioxide (CO₂) is an ideal one-carbon source owing to its nontoxicity, abundance, availability, and recyclability.

Kolbe-Schmitt type reaction under ambient conditions mediated by an organic base

The combined use of an organic base for resorcinols realized a Kolbe-Schmitt type reaction under ambient conditions. When resorcinols (3-hydroxyphenol derivatives) were treated with DBU under a carbon dioxide atmosphere, nucleophilic addition to carbon dioxide proceeded to afford the corresponding salicylic acid derivatives in high yields.

C-H Bond Carboxylation with Carbon Dioxide

Carbon dioxide is a nontoxic, renewable, and abundant C₁ source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chemical transformation of CO₂ with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivatives. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp² )-H bonds of (hetero)arenes, vinylic C(sp² )-H bonds, the ipso-C(sp² )-H bonds of the diazo group, aldehyde C(sp² )-H bonds, α-C(sp³ )-H bonds of the carbonyl group, γ-C(sp³ )-H bonds of the carbonyl group, C(sp³ )-H bonds adjacent to nitrogen atoms, C(sp³ )-H bonds of o-alkyl phenyl ketones, allylic C(sp³ )-H bonds, C(sp³ )-H bonds of methane, and C(sp³ )-H bonds of halogenated aliphatic hydrocarbons. In addition, multicomponent reactions, tandem reactions, and key theoretical studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochemical, and light-driven methods are highlighted.

Recent advances of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) in photocatalytic transformations

In this review, the recent advances of the application of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as a photoredox catalyst in the past three years (2016–2018) for various organic reactions are summarized.

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.

Synthesis of Oxazolidin-2-ones from Unsaturated Amines with CO2 by Using Homogeneous Catalysis

Carbon dioxide (CO₂ ), a well-known greenhouse gas, is also a nontoxic, readily accessible, and renewable one-carbon (C1) source. However, owing to its thermodynamic stability and kinetic inertness, the efficient utilization of CO₂ is challenging. Much effort has been devoted to achieving efficient and selective organic transformations of CO₂ . Recently, the synthesis of important oxazolidin-2-ones from unsaturated amines by using CO₂ has attracted much attention and been heavily studied. This Focus Review presents recent advances in this area by using homogenous catalysis. The cyclization of amines that contain alkynes, alkenes, and allenes with CO₂ is discussed, and possible reaction mechanisms and applications of these transformations are also described.

Reactions of secondary propargylamines with heteroallenes for the synthesis of diverse heterocycles

This focused review aims to summarize recent developments in the processes involving additions of secondary propargylamines to various heteroallenes and subsequent transition metal-catalyzed or electrophile-mediated cyclizations.

Pd-catalyzed carbonylation of aryl C–H bonds in benzamides with CO2

Herein, we report the first Pd-catalyzed carbonylation of unactivated aryl C–H bonds in benzamides under 1 atm of CO₂ to directly afford important phthalimides.

Highly Regio- and Enantioselective Copper-Catalyzed Reductive Hydroxymethylation of Styrenes and 1,3-Dienes with CO2

Herein, we report a highly regio- and enantioselective copper-catalyzed reductive hydroxymethylation of styrenes and 1,3-dienes with 1 atm of CO₂. Diverse important chiral homobenzylic alcohols were readily prepared from styrenes. Moreover, a variety of 1,3-dienes also were converted to chiral homoallylic alcohols with high yields and excellent regio-, enantio-, and Z/E-selectivities. The utility of this transformation was demonstrated by a broad range of styrenes and 1,3-dienes, facile product modification, and synthesis of bioactive compounds (R)-(-)-curcumene and (S)-(+)-ibuprofen. Mechanistic studies demonstrated the carboxylation of phenylethylcopper complexes with CO₂ as one key step.

Photochemical Carboxylation of Activated C(sp3 )-H Bonds with CO2

From ugly duckling to beautiful C1: Although CO₂ may represent an ideal C1 source, it is challenging to use it as a raw material and direct carboxylation with CO₂ has mainly been confined to highly reactive species. However, recent significant breakthroughs have been made in photochemical carboxylation of challenging, un-acidic, C(sp³ )-H bonds, including benzylic, allylic and amine C-H bonds.

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.

Mechanistic study of the rhodium-catalyzed carboxylation of simple aromatic compounds with carbon dioxide

A detailed mechanistic study of the rhodium-catalyzed carboxylation of aromatic compounds was carried out to clarify the unique characteristics of this reaction.

A detailed mechanism of the Rh(i)-catalyzed carboxylation of simple aromatic compounds via C–H bond activation was investigated. Kinetic studies with model compounds of the postulated key intermediates revealed that 14-electron complexes, RhMe(dcype) and RhPh(dcype), participated in the C–H bond activation step and the carboxylation step, respectively. Interestingly, the undesired carboxylation of RhMe(dcype) to give acetic acid was found to be much faster than the desired C–H bond activation reaction under stoichiometric conditions, however, the C–H bond activation reaction could occur under catalytic conditions. Careful controlled experiments revealed that C–H bond activation using RhMe(dcype) became competitive with its direct carboxylation under the condition that the concentration of CO₂ in the liquid phase was rather low. This factor could be controlled to some extent by mechanical factors such as the stirring rate and the shape of the reaction vessel. The resting state of the rhodium species under catalytic conditions was found to be [RhCl(dcype)]₂, and the proposed intermediates such as RhMe(dcype) and Rh(OBz)(dcype) were readily converted to the most stable state, [RhCl(dcype)]₂, via transmetallation with [Al]–Cl species, thus preventing the decomposition of the active catalytic species.

Amine modified mesoporous Al2O3@MCM-41: an efficient, synergetic and recyclable catalyst for the formylation of amines using carbon dioxide and DMAB under mild reaction conditions

A novel amine modified meso Al₂O₃@MCM-41 catalyst was investigated for the synthesis of formamides from 1°/2° aliphatic as well as aromatic amines with CO₂, using DMAB.

A hydroxyl-functionalized microporous organic polymer for capture and catalytic conversion of CO2

A novel hydroxyl-functionalized microporous organic polymer (HF-MOP) exhibited good CO₂ capture performance and excellent catalytic activity in cycloaddition reaction.

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.

Silver(I)-Catalyzed Synthesis of β-Oxopropylcarbamates from Propargylic Alcohols and CO2 Surrogate: A Gas-Free Process

The utilization of carbon dioxide poses major challenges owing to its high thermodynamic stability and kinetic inertness. To circumvent these problems, a simple reaction system is reported comprising ammonium carbamates as carbon dioxide surrogates, propargylic alcohols, and a silver(I) catalyst, for the effective conversion of a wide range of alcohols and secondary amines into the corresponding β-oxopropylcarbamates. A key feature of this strategy includes quantitative use of a carbon resource with high product yields under gas-free and mild reaction conditions. Notably, this catalytic protocol also works well for the carboxylative cyclization of propargylic amines and carbon dioxide surrogates to afford 2-oxazolidinones.

DBU-promoted carboxylative cyclization of o-hydroxy- and o-acetamidoacetophenone

The carboxylative cyclization of o-hydroxy- and o-acetamidoacetophenone with carbon dioxide promoted by the organic base 1,8-diazabicycloundec-7-ene (DBU) is reported. This reaction provides convenient access to the biologically important compounds 4-hydroxy-2H-chromen-2-one and 4-hydroxy-2(1H)-quinolinone in moderate to good yields using carbon dioxide as the carboxylation reagent. An acyl migration from nitrogen to carbon is observed in the reaction of o-acetamidoacetophenone.

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.

Carboxylic acid derivatives via catalytic carboxylation of unsaturated hydrocarbons: whether the nature of a reductant may determine the mechanism of CO2incorporation?

Advances and recent breakthroughs in catalytic synthesis of carboxylic acids and their derivatives starting from unsaturated hydrocarbons are discussed.

Organoantimony and organobismuth complexes for CO2fixation

The utilization of organoantimony and organobismuth complexes in CO₂fixation is reviewed in this article.

Direct carboxylation of simple arenes with CO2 through a rhodium-catalyzed C–H bond activation

Direct carboxylation of various simple arenes under atmospheric pressure of CO₂ is achieved through a rhodium-catalyzed C–H bond activation without the assistance of a directing group.