Carbonylations of Alkenes with CO Surrogates

Decarbonylative ether dissection by iridium pincer complexes

A unique chain-rupturing transformation that converts an ether functionality into two hydrocarbyl units and carbon monoxide is reported, mediated by iridium(i) complexes supported by aminophenylphosphinite (NCOP) pincer ligands. The decarbonylation, which involves the cleavage of one C-C bond, one C-O bond, and two C-H bonds, along with formation of two new C-H bonds, was serendipitously discovered upon dehydrochlorination of an iridium(iii) complex containing an aza-18-crown-6 ether macrocycle. Intramolecular cleavage of macrocyclic and acyclic ethers was also found in analogous complexes featuring aza-15-crown-5 ether or bis(2-methoxyethyl)amino groups. Intermolecular decarbonylation of cyclic and linear ethers was observed when diethylaminophenylphosphinite iridium(i) dinitrogen or norbornene complexes were employed. Mechanistic studies reveal the nature of key intermediates along a pathway involving initial iridium(i)-mediated double C-H bond activation.

From Alkynes to Heterocycles through Metal-Promoted Silylformylation and Silylcarbocyclization Reactions

Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically active molecules. Most of these contain a C=O moiety which can be easily introduced using carbonylative reaction conditions. In this field, intramolecular silylformylation and silylcarbocyclization reactions may afford heterocyclic compounds containing a carbonyl functional group together with a vinylsilane moiety which can be further transformed. Considering these two aspects, in this review a detailed analysis of the literature data regarding the application of silylformylation and silylcarbocyclization reactions to the synthesis of several heterocyclic derivatives is reported.

Rapid Organocatalytic Formation of Carbon Monoxide: Application towards Carbonylative Cross Couplings

Herein, the first organocatalytic method for the transformation of non‐derivatized formic acid into carbon monoxide (CO) is introduced. Formylpyrrolidine (FPyr) and trichlorotriazine (TCT), which is a cost‐efficient commodity chemical, enable this decarbonylation. Utilization of dimethylformamide (DMF) as solvent and catalyst even allows for a rapid CO generation at room temperature. Application towards four different carbonylative cross coupling protocols demonstrates the high synthetic utility and versatility of the new approach. Remarkably, this also comprehends a carbonylative Sonogashira reaction at room temperature employing intrinsically difficult electron‐deficient aryl iodides. Commercial ¹³C‐enriched formic acid facilitates the production of radiolabeled compounds as exemplified by the pharmaceutical Moclobemide. Finally, comparative experiments verified that the present method is highly superior to other protocols for the activation of carboxylic acids.

Nickel-catalyzed carboxylation of aryl iodides with lithium formate through catalytic CO recycling

A protocol for the Ni-catalyzed carboxylation of aryl iodides with formate has been developed with good functional group compatibility for the synthesis of a variety of aromatic carboxylic acids under mild conditions. The reaction tolerates other functionalities for cross-coupling, such as aryl bromide, aryl chloride, aryl tosylate, and aryl pinacol boronate. The reaction proceeds through a carbonylation process with in situ generated carbon monoxide in the presence of a catalytic amount of acetic anhydride and lithium formate, avoiding the use of gaseous CO. The strategy of CO recycling in catalytic amounts is critical for the success of the reaction.

Palladium-catalyzed carbonylative synthesis of arylacetamides from benzyl formates and tertiary amines

A palladium-catalyzed carbonylative synthesis of arylacetamides via a C–N bond cleavage of tertiary amines with benzyl formates as the CO source has been disclosed. A variety of arylacetamides were obtained in very good yields under oxidant-free conditions.

Carbonylative synthesis of heterocycles involving diverse CO surrogates

Recent advances in the carbonylative synthesis of heterocycles by using diverse CO surrogates as sources of CO are summarized and discussed.

Efficient methanol carbonylation to methyl acetate catalyzed by a cyclic(alkyl)(amino)carbene iridium complex

An efficient cyclic(alkyl)(amino) carbene iridium complex (C-2) was developed for methanol carbonylation to methyl acetate (MA) directly.

Ex situ gas generation for lab scale organic synthesis

This review discusses recent examples of ex situ generated gaseous reagents, and their use in organic synthesis.

Palladium-catalyzed carbonylations of highly substituted olefins using CO-surrogates

CO surrogate chemistry: General protocols for alkoxycarbonylations of highly substituted olefins with paraformaldehyde and methyl formate are reported, allowing the performance of carbonylation reactions in all labs and for all kinds of substrates.

Low-Temperature Reverse Water-Gas Shift Process and Transformation of Renewable Carbon Resources to Value-Added Chemicals

The use of CO₂ instead of toxic CO in the production of important chemicals has attracted widespread interest, and the reverse water-gas shift reaction (RWGSR) is the key step for this kind of processes. Although the thermodynamic limitations are overcome by the reaction of CO with other compounds, the temperature of most reactions involving RWGSR is usually very high owing to the inertness of CO₂ . Herein, it was found that Ru₃ (CO)₁₂ could catalyze the RWGSR in the ionic liquid HMimBF₄ without ligand or promoter, and CO could be produced at 80 °C, which was much lower than the temperatures reported to date. Detailed studies showed that the BF₄ ^- in the ionic liquid played a crucial role in the low-temperature RWGSR. Based on the low-temperature RWGSR, three important routes to transform CO₂ into valuable chemicals were developed, including synthesis of xanthone from CO₂ and diaryl ethers, synthesis of phenol and acetic acid from CO₂ and anisole, and production of acetic acid from CO₂ and lignin. The reactions could occur at temperature as low as 80 °C, and low-temperature RWGSR was essential for the reactions under mild conditions. The strategy opens the way to produce value-added chemicals by using CO₂ and H₂ as feedstocks under low temperature.

Continuous Pd-Catalyzed Carbonylative Cyclization Using Iron Pentacarbonyl as a CO Source

This work discloses a continuous flow carbonylation reaction using iron pentacarbonyl as source of CO. The described transformation using this surrogate was designed for use in commonly accessible flow equipment. Optimized conditions were applied to a scalable synthesis of the natural compound isolated from perianal glandular pheromone secretion of the African civet cat. In addition, a flow Pd-catalyzed carbonylation of aryl halides is successfully reported.

COtab: Expedient and Safe Setup for Pd-Catalyzed Carbonylation Chemistry

Bench-stable tablets (COtabs) have been developed for the rapid and safe production of carbon monoxide. The tablets can be made in less than 5 min without the use of a glovebox and only require a stock solution of an amine base to liberate a specific quantity of CO in a two-chamber system. The COtabs were tested in five different carbonylation reactions and provided similar yields compared to literature procedures. Finally, a gram-scale reaction was conducted, as well as ¹³C-isotope labeling of the anticancer drug, olaparib.

Cobaltaelectro-Catalyzed C-H Activation with Carbon Monoxide or Isocyanides

Electrochemical oxidative C-H/N-H activations with isocyanides have been realized with a versatile cobalt catalyst. The widely applicable cobalt catalysis manifold further enabled electrooxidative C-H/N-H carbonylations with carbon monoxide under ambient conditions. The C-H functionalizations were efficiently realized with ample scope and outstanding functional group tolerance in a user-friendly undivided cell setup.

Chloroform as a CO surrogate: applications and recent developments

The carbonyl moiety is one of the indispensable sub-units in organic synthesis with significant applications in medicinal as well as materials chemistry. Hence the insertion of a carbonyl group via simple and highly efficient routes has been one of the most challenging tasks for organic chemists. Though the direct utilisation of CO gas in carbonylation is the fundamental procedure for the construction of carbonyl compounds, it has certain drawbacks due to its toxic and explosive nature. As a result, the need for cheap and efficient CO surrogates has gained much attention nowadays by which CO gas can be easily generated in situ or ex situ. In this review we discuss the advantages of chloroform as CO surrogate and have surveyed recent carbonylation reactions where chloroform has been used as CO source.