Palladium-Catalyzed Double Carbonylation Using Near Stoichiometric Carbon Monoxide: Expedient Access to Substituted 13C2-Labeled Phenethylamines

De Novo Synthesis of α-Ketoamides via Pd/TBD Synergistic Catalysis

Precisely controlling the product selectivity of a reaction is an important objective in organic synthesis. α-Ketoamides are vital intermediates in chemical transformations and privileged motifs in numerous drugs, natural products, and biologically active molecules. The selective synthesis of α-ketoamides from feedstock chemicals in a safe and operationally simple manner under mild conditions is a long-standing catalysis challenge. Herein, an unprecedented TBD-switched Pd-catalyzed double isocyanide insertion reaction for assembling ketoamides in aqueous DMSO from (hetero)aryl halides and pseudohalides under mild conditions is reported. The effectiveness and utility of this protocol are demonstrated by its diverse substrate scope (93 examples), the ability to late-stage modify pharmaceuticals, scalability to large-scale synthesis, and the synthesis of pharmaceutically active molecules. Mechanistic studies indicate that TBD is a key ligand that modulates the Pd-catalyzed double isocyanide insertion process, thereby selectively providing the desired α-ketoamides in a unique manner. In addition, the imidoylpalladium(II) complex and α-ketoimine amide are successfully isolated and determined by X-ray analysis, confirming that they are probable intermediates in the catalytic pathway.

Transition Metal-Free N-S Bond Cleavage and C-N Bond Activation of Ugi-Adducts for Rapid Preparation of Primary Amides and α-Ketoamides

A novel method of transition metal-free N-S bond cleavage and subsequent C-N bond activation of Ugi-adducts was developed. Diverse primary amides and α-ketoamides were prepared in a rapid, step-economical and highly efficient manner in two steps. This strategy features excellent chemoselectivity, high yield and functional-group tolerance. Primary amides derived from the pharmaceuticals probenecid and febuxostat were prepared. This method opens a new pathway for the simultaneous synthesis of primary amides and α-ketoamides in an environmentally friendly manner.

Amine Activation: "Inverse" Dipeptide Synthesis and Amide Function Formation through Activated Amino Compounds

A copper(II)/HOBt-catalyzed procedure for the synthesis of dipeptides and "general" amides has been developed using microwave irradiation to considerably hasten the reaction. As an alternative to using traditional carboxylic acid activation, the method relies on the use of N-acyl imidazoles as activated amino partners. By doing so, a nonconventional way to reach dipeptides and amides has been proposed through the challenging and less studied N → C direction synthesis. A series of dipeptides and "general" amides have been successfully synthesized, and the applicability of the method has been illustrated in gram-scale syntheses. The mild reaction conditions proposed are completely adequate for couplings in the presence of sensitive amino acids, affording the products without detectable racemization. Furthermore, experimental observations prompted us to propose a plausible reaction pathway for the couplings.

One-Pot Synthesis of α-Ketoamides from α-Keto Acids and Amines Using Ynamides as Coupling Reagents

A one-pot strategy for α-keto amide bond formation have been developed by using ynamides as coupling reagents under extremely mild reaction conditions. Diversely structural α-ketoamides were afforded in up to 98% yield for 36 examples. This reaction features advantages such as practical coupling procedure, wide functional group tolerance, and extremely mild conditions and has potential applications in synthetic and medicinal chemistry.

A MOF Multifunctional Cargo Vehicle for Reactive Gas Delivery and Catalysis

Efficient delivery of reactive and toxic gaseous reagents to organic reactions was studied using metal-organic frameworks (MOFs). Simultaneous cargo vehicle and catalytic capabilities of several MOFs were probed for the first time using the examples of  aromatization, aminocarbonylation, and carbonylative Suzuki-Miyaura coupling reactions. These reactions highlight that MOFs can serve a dual role as a gas cargo vehicle and a catalyst,  leading to product formation with yields similar to reactions employing pure gases. Furthermore, the MOFs can be recycled without sacrificing product yield, while simultaneously maintaining crystallinity. The reported findings were supported crystallographically and spectroscopically (e.g.,  diffuse reflectance infrared Fourier transform spectroscopy), foreshadowing a pathway for the development of multifunctional MOF-based reagent-catalyst cargo vessels for reactive reagents, as an attractive alternative to the use of toxic pure gases or gas generators.

Rapid assembly of α-ketoamides through a decarboxylative strategy of isocyanates with α-oxocarboxylic acids under mild conditions

A simple and practical method for α-ketoamide synthesis via a decarboxylative strategy of isocyanates with α-oxocarboxylic acids is described. The reaction proceeds at room temperature under mild conditions without an oxidant or an additive, showing good substrate scope and functional compatibility. Moreover, the applicability of this method was further demonstrated by the synthesis of various bioactive molecules and different application examples through a two-step one-pot operation.

POP-Pd(ii) catalyzed easy and safe in situ carbonylation towards the synthesis of α-ketoamides from secondary cyclic amines utilizing CHCl3 as a carbon monoxide surrogate

POP-palladium(ii) was synthesized for the in situ carbonylation of aryl iodides and secondary cyclic amine to the respective α-ketoamides.

5-Bromo-norborn-2-en-7-one derivatives as a carbon monoxide source for palladium catalyzed carbonylation reactions

Norbornenone (5b), obtained from the reaction of 2,5-dimethyl-3,4-diphenylcyclopentadienone dimer (3) with bromomaleic anhydride (4b), provides an excellent base-triggered source of carbon monoxide for palladium-catalysed carbonylation reactions. Aminocarbonylation, ketoamide synthesis, and Suzuki–Miyaura reactions of aryl iodides carried out in a two-chamber reaction vessel gave good to excellent yields of carbonylated products.

Norbornenone (5b), obtained from the reaction of 2,5-dimethyl-3,4-diphenylcyclopentadienone dimer (3) with bromomaleic anhydride (4b), provides an excellent base-triggered source of carbon monoxide for palladium-catalysed carbonylation reactions.

Copper-catalyzed oxidative cleavage of Passerini and Ugi adducts in basic medium yielding α-ketoamides

The present study provides an insight into the reactivity of Passerini and Ugi adducts in basic medium leading to α-ketoamides.

Chemoenzymatic Synthesis of Synthes as Precursors for Enantiopure Clenbuterol and Other β2 Agonists

Clenbuterol is a β2-agonist used in the veterinary treatment of asthma in several countries. The drug is listed on the World Antidoping Agency’s prohibited list due to its effect on increased protein synthesis in the body. However, racemic clenbuterol has recently been shown to reduce the risk of Parkinson’s disease. In order to reveal which one (or both) of the enantiomers that cause this effect, pure enantiomers need to be separately studied. (R)-1-(4-Amino-3,5-dichlorophenyl)-2-bromoethan-1-ol has been synthesised in 93% enantiomeric excess (ee) by asymmetric reduction of the corresponding ketone catalysed by a ketoreductase and nicotinamide adenine dinucleotide phosphate (NADPH) as the cofactor in dimethyl sulfoxide (DMSO). (S)-N-(2,6-Dichloro-4-(1-hydroxyethyl)phenyl)acetamide has been synthesised in >98% ee by the same system. Both synthons are potential precursors for clenbuterol enantiomers.

Viable pathways for the oxidative addition of iodobenzene to palladium(0)-triphenylphosphine-carbonyl complexes: a theoretical study

The oxidative addition of 4-substituted iodobenzenes on Pd(0) catalysts under CO atmosphere was investigated by means of density functional calculations employing the M06//B97-D3 level of theory. The 18-electron triphenylphosphine-tricarbonyl complex was found to be the global minimum. Several coordinatively unsaturated species are predicted to be present both in N,N-dimethylformamide and toluene solution. In terms of activating iodobenzene, bis(triphenylphosphine)palladium(0) was proved to be the most active. However, due to its lower thermodynamic stability, it is slightly inferior to the Pd-triphenylphosphine-carbonyl complex, which is predicted to react with a free energy of activation of 23.2 kcal mol^-1 with respect to the initial resting state tetrakis(triphenylphosphine)palladium(0). The effect of 4-substituents of iodobenzene on reaction energetics is also discussed. The activity of the Pd(0) catalyst was found to be governed by the donor-acceptor strength of the ancillary ligands: the barrier decreases with increasing basicity and decreasing back-donating capability.

Copper-catalyzed carbonylative transformations of indoles with hexaketocyclohexane

With hexaketocyclohexane octahydrate as the carbon monoxide source, a novel procedure for copper-catalyzed direct double carbonylation of indoles has been established.

Scalable carbon dioxide electroreduction coupled to carbonylation chemistry

Significant efforts have been devoted over the last few years to develop efficient molecular electrocatalysts for the electrochemical reduction of carbon dioxide to carbon monoxide, the latter being an industrially important feedstock for the synthesis of bulk and fine chemicals. Whereas these efforts primarily focus on this formal oxygen abstraction step, there are no reports on the exploitation of the chemistry for scalable applications in carbonylation reactions. Here we describe the design and application of an inexpensive and user-friendly electrochemical set-up combined with the two-chamber technology for performing Pd-catalysed carbonylation reactions including amino- and alkoxycarbonylations, as well as carbonylative Sonogashira and Suzuki couplings with near stoichiometric carbon monoxide. The combined two-reaction process allows for milligram to gram synthesis of pharmaceutically relevant compounds. Moreover, this technology can be adapted to the use of atmospheric carbon dioxide.

Electroreduction of CO₂ to CO is a potential valorisation pathway of carbon dioxide for fine chemicals production. Here, the authors show a user-friendly device that couples CO₂ electroreduction with carbonylation chemistry for up to gram scale synthesis of pharmaceuticals even under atmospheric CO₂.

nBu4NI-Mediated oxidation of methyl ketones to α-ketoamides: using ammonium, primary and secondary amine-salt as an amine moiety

Presented is the first example of synthesizing an array of primary-, secondary-, and tertiary-α-ketoamides in moderate to excellent yields with a catalyst nBu₄NI from methyl ketones and amine/ammonium salts under mild conditions using oxidant TBHP.

The one-pot synthesis of quinolines via Co(iii)-catalyzed C–H activation/carbonylation/cyclization of anilines

A new and versatile Co(iii)-catalyzed C–H activation/carbonylation/cyclization cascade reaction has been disclosed.

The Development and Application of Two-Chamber Reactors and Carbon Monoxide Precursors for Safe Carbonylation Reactions

Low molecular weight gases (e.g., carbon monoxide, hydrogen, and ethylene) represent vital building blocks for the construction of a wide array of organic molecules. Whereas experimental organic chemists routinely handle solid and liquid reagents, the same is not the case for gaseous reagents. Synthetic transformations employing such reagents are commonly conducted under pressure in autoclaves or under atmospheric pressure with a balloon setup, which necessitates either specialized equipment or potentially hazardous and nonrecommended installations. Other safety concerns associated with gaseous reagents may include their toxicity and flammability and, with certain gases, their inability to be detected by human senses. Despite these significant drawbacks, industrial processes apply gaseous building blocks regularly due to their low cost and ready availability but nevertheless under a strictly controlled manner. Carbon monoxide (CO) fits with all the parameters for being a gas of immense industrial importance but with severe handling restrictions due to its inherent toxicity and flammability. In academia, as well as research and development laboratories, CO is often avoided because of these safety issues, which is a limitation for the development of new carbonylation reactions. With our desire to address the handling of CO in a laboratory setting, we designed and developed a two-chamber reactor (COware) for the controlled delivery and utilization of stoichiometric amounts of CO for Pd-catalyzed carbonylation reactions. In addition to COware, two stable and solid CO-releasing molecules (COgen and SilaCOgen) were developed, both of which release CO upon activation by either Pd catalysis or fluoride addition, respectively. The unique combination of COware with either COgen or SilaCOgen provides a simple reactor setup enabling synthetic chemists to easily perform safe carbonylation chemistry without the need for directly handling the gaseous reagent. With this technology, an array of low-pressure carbonylations were developed applying only near stoichiometric amounts of carbon monoxide. Importantly, carbon isotope variants of the CO precursors, such as (13)COgen, Sila(13)COgen, or even (14)COgen, provide a simple means for performing isotope-labeling syntheses. Finally, the COware applicability has been extended to reactions with other gases, such as hydrogen, CO2, and ethylene including their deuterium and (13)C-isotopically labeled versions where relevant. The COware system has been repeatedly demonstrated to be a valuable reactor for carrying out a wide number of transition metal-catalyzed transformations, and we believe this technology will have a significant place in many organic research laboratories.

Palladium-Catalyzed Hydroamidocarbonylation of Olefins to Imides

Carbonylation reactions allow the efficient synthesis of all kinds of carbonyl-containing compounds. Here, we report a straightforward synthesis of various imides from olefins and CO for the first time. The established hydroamidocarbonylation reaction affords imides in good yields (up to 90 %) and with good regioselectivity (up to 99:1) when applying different alkenes and amides. The synthetic potential of the method is highlighted by the synthesis of Aniracetam by intramolecular hydroamidocarbonylation.

Catalytic chemical amide synthesis at room temperature: one more step toward peptide synthesis

An efficient method has been developed for direct amide bond synthesis between carboxylic acids and amines via (2-(thiophen-2-ylmethyl)phenyl)boronic acid as a highly active bench-stable catalyst. This catalyst was found to be very effective at room temperature for a large range of substrates with slightly higher temperatures required for challenging ones. This methodology can be applied to aliphatic, α-hydroxyl, aromatic, and heteroaromatic acids as well as primary, secondary, heterocyclic, and even functionalized amines. Notably, N-Boc-protected amino acids were successfully coupled in good yields with very little racemization. An example of catalytic dipeptide synthesis is reported.

Recent advances in the transition metal catalyzed carbonylation of alkynes, arenes and aryl halides using CO surrogates

Transition metal catalyzed carbonylation reactions using carbon monoxide as the C-1 source have occupied an all important position in catalysis which is subsequently related to organic synthesis and industrial synthesis of molecules.

Palladium(0)-catalyzed single and double isonitrile insertion: a facile synthesis of benzofurans, indoles, and isatins

A palladium(0)-catalyzed cascade process consisting of isonitrile insertion and α-Csp(3)-H cross-coupling can be achieved for the synthesis of benzofurans and indoles. The construction of isatins by a Pd-catalyzed cascade reaction incorporating double isonitrile insertion, amination, and hydrolysis has also been achieved. The key features of this work include diverse heterocycle synthesis, phosphine-ligand-free reaction conditions, a one-pot procedure, simple and commercially available starting materials, broad functional-group compatibility, and moderate to good reaction yields.

Mild Pd-catalyzed aminocarbonylation of (hetero)aryl bromides with a palladacycle precatalyst

A palladacyclic precatalyst is employed to cleanly generate a highly active XantPhos-ligated Pd-catalyst. Its use in low temperature aminocarbonylations of (hetero)aryl bromides provides access to a range of challenging products in good to excellent yields with low catalyst loading and only a slight excess of CO. Some products are unattainable by traditional carbonylative coupling.