Exploiting Chloroform-COware Chemistry for Pd-Catalyzed Carbonylation of Naturally Occurring and Medicinally Relevant Phenols

In this study, a ligand-free palladium-catalyzed carbonylation of phenols is conducted under ambient conditions, utilizing the "Chloroform-COware" chemistry. The developed methodology enables the conversion of diverse medicinally relevant phenols, encompassing both natural and synthetic derivatives, into their respective aryl ester counterparts. This transformation is achieved through the reaction with a broad spectrum of aryl and heteroaryl iodides. The protocol is characterized by its simplicity, generality, and wide substrate scope, delivering bioactive aryl ester derivatives in good to excellent yields. A direct comparison with the one-pot approach, resulting in poor yields of aryl esters, highlights the superior efficiency of the two-chamber setup (COware). Moreover, we successfully applied this two-chamber technique for gram-scale synthesis and postmodification of the synthesized ester to a pharmaceutically important benzocoumarin core.

Perfluorooxosulfate Salts as SOF4-Gas-Free Precursors to Multidimensional SuFEx Electrophiles

Sulfur(VI) Fluoride Exchange (SuFEx) chemistry stands as a well-established method for swiftly constructing complex molecules in a modular fashion. An especially promising segment of this toolbox is reserved for multidimensional SuFEx hubs: three or more substituents pluggable into a singular SVI centre to make 'beyond-linear' clicked constructions. Sulfurimidoyl difluorides (RNSOF2) stand out as the prime example of this, however their preparation from the scarcely available thionyl tetrafluoride (SOF4) limits this chemistry to only a few laboratories with access to this gas. In this work, we identify silver pentafluorooxosulfate (AgOSF5) as a viable SuFEx hub with reactivity equal to SOF4. The AgF2-mediated oxidation of SOCl2 gives rise to the hexacoordinate AgOSF5 adduct, which in contact with primary amines produces the sulfurimidoyl fluorides in high yields. In addition, we have found this workflow to be fully extendable to the trifluoromethyl homologue, AgOSF4CF3, and we propose the use of AgOSF4X salts as a general route to azasulfur SuFEx electrophiles from commercial starting materials.

An Extrusion Strategy for On-Demand SF5Cl Gas Generation from a Commercial Disulfide

Herein we report a novel methodology for the ex situ generation of SF5Cl by employing 4,4'-dipyridyl disulfide as a safe commercial reagent, obviating the need for lecture bottles. The method is applicable to certain SF5Cl-involving transformations by using a two-chamber reactor. Moreover, easily applying SF5Cl in different solvents is rendered feasible, while avoiding the use of glovebox techniques. This report also suggests 1H-19F HOESY as a simple and fast stereochemistry indication for chloropentafluorosulfanylated olefins.

Ambient-Temperature, Metal-Free, CDI-Mediated Ex-Situ Conversion of Acids to Amides: A Useful Late-Stage Strategy

An efficient ex-situ method for the amidation of carboxylic acids mediated by CDI has been disclosed herewith. This metal-free strategy is performed at ambient temperature and can be applied effectively for late-stage modification of amino acids and APIs.

Carbonylative Transformations Using a DMAP-Based Pd-Catalyst through Ex Situ CO Generation

A phosphine-free, efficient protocol for aminocarbonylation and carbonylative Suzuki-Miyaura coupling has been developed using a novel palladium complex, [PdII(DMAP)2(OAc)2]. The complex was successfully synthesized using a stoichiometric reaction between PdII(OAc)2 and DMAP in acetone at room temperature and characterized using single-crystal X-ray analysis. Only 5 mol % catalyst loading was sufficient for effective carbonylative transformations. "Chloroform-COware" chemistry was utilized for safe and facile insertion of the carbonyl unit using chloroform as an inexpensive CO source in a two-chamber setup. Various value-added pharmaceutically relevant compounds such as CX-516, CX-546, and farampator were synthesized using the technique. Furthermore, the commercially designed COware was engineered to COware-RB setup for sequential one-pot synthesis of indenoisoquinolines (topoisomerase I inhibitors).

Handling fluorinated gases as solid reagents using metal-organic frameworks

Fluorine is an increasingly common substituent in pharmaceuticals and agrochemicals because it improves the bioavailability and metabolic stability of organic molecules. Fluorinated gases represent intuitive building blocks for the late-stage installation of fluorinated groups, but they are generally overlooked because they require the use of specialized equipment. We report a general strategy for handling fluorinated gases as benchtop-stable solid reagents using metal-organic frameworks (MOFs). Gas-MOF reagents are prepared on gram-scale and used to facilitate fluorovinylation and fluoroalkylation reactions. Encapsulation of gas-MOF reagents within wax enables stable storage on the benchtop and controlled release into solution upon sonication, which represents a safer alternative to handling the gas directly. Furthermore, our approach enables high-throughput reaction development with these gases.

Rediscovering Cyanogen Gas for Organic Synthesis: Formation of 2-Cyanothiazole Derivatives

The expeditious synthesis of an API building block, 2-cyanothiazole, from cyanogen gas and a readily available dithiane is reported. A previously undisclosed partially saturated intermediate is formed, which can be further functionalized and isolated by the acylation of the hydroxy group. Dehydration using trimethylsilyl chloride furnished 2-cyanothiazole, which could be further converted to the corresponding amidine. The sequence provided a 55% yield over 4 steps. We envision that this work will spark further interest in cyanogen gas as a reactive and cost-effective synthetic reagent.

Palladium-Catalyzed Aminocarbonylation of Isoquinolines Utilizing Chloroform-COware Chemistry

The carbonyl group forms an integral part of several drug molecules and materials; hence, synthesis of carbonylated compounds remains an intriguing area of research for synthetic and medicinal chemists. Handling toxic CO gas has several limitations; thus, using safe and effective techniques for in or ex situ generation of carbon monoxide from nontoxic and cheap precursors is highly desirable. Among several precursors that have been explored for the generation of CO gas, chloroform can prove to be a promising CO surrogate due to its cost-effectiveness and ready availability. However, the one-pot chloroform-based carbonylation reaction requires strong basic conditions for hydrolysis of chloroform that may affect functional group tolerability of substrates and scale-up reactions. These limitations can be overcome by a two-chamber reactor (COware) that can be utilized for ex situ CO generation through hydrolysis of chloroform in one chamber and facilitating safe carbonylation reactions in another chamber under mild conditions. The versatility of this "Chloroform-COware" technique is explored through palladium-catalyzed aminocarbonylation of medicinally relevant heterocyclic cores, viz., isoquinoline and quinoline.

Introducing SuFNucs: Sulfamoyl-Fluoride-Functionalized Nucleosides That Undergo Sulfur Fluoride Exchange Reaction

The reaction between ribonucleosides and ex situ generated sulfonyl fluoride has been developed. The reaction takes place at the −NH₂ groups of nucleobases, and the resulting nucleosides are equipped with a sulfamoyl fluoride moiety, dubbed SuFNucs. These species undergo a selective sulfur fluoride exchange (SuFEx) reaction with various amines, leading to sulfamide-functionalized derivatives of adenosine, guanosine, and cytidine (SulfamNucs). The scope and examples of further SuFNucs fuctionalization leading to nucleotides, oligonucleotides, and peptide–nucleoside conjugates are presented.

Transfer hydrogenation of nitroarenes using cellulose filter paper-supported Pd/C by filtration as well as sealed methods

A reductive filter paper for selective nitro reduction has been prepared by modification of a pristine cellulose filter paper by Pd/C nanoparticles, as a portable catalyst. The reaction was performed in two different set-ups including (i) filtration and (ii) sealed systems, in the presence of ammonium formate and ex situ generated hydrogen gas reducing agents, respectively. In the sealed system in the presence of H₂ gas, the halogenated nitroarenes were completely reduced, while in the filtration system, different derivatives of the nitroarenes were selectively reduced to aryl amines. In both systems, the reduction of nitroarenes to aryl amines was performed with high efficiency and selectivity, comparable to a heterogeneous system. Reaction parameters were comprehensively designed using Design Expert software and then studied. The properties of the catalytic filter paper were studied in detail from the points of view of swellability, shrinkage, reusability, and stability against acidic, alkaline, and oxidative reagents.

A novel and efficient catalytic filtration has been developed for the selective reduction of nitro compounds on a Pd/C-doped cellulose filter paper.

Thermal Mapping of Self-Promoted Calcium Carbide Reactions for Performing Energy-Economic Processes

The syntheses of various chemical compounds require heating. The intrinsic release of heat in exothermic processes is a valuable heat source that is not effectively used in many reactions. In this work, we assessed the released heat during the hydrolysis of an energy-rich compound, calcium carbide, and explored the possibility of its usage. Temperature profiles of carbide hydrolysis were recorded, and it was found that the heat release depended on the cosolvent and water/solvent ratio. Thus, the release of heat can be controlled and adjusted. To monitor the released heat, a special tube-in-tube reactor was assembled using joining part 3D-printed with nylon. The thermal effect of the reaction was estimated using a thermoimaging IR monitor. It was found that the kinetics of heat release are different when using mixtures of water with different solvents, and the maximum achievable temperature depends on the type of solvent and the amount of water and carbide. The possibility of using the heat released during carbide hydrolysis to initiate a chemical reaction was tested using a hydrothiolation reaction—the nucleophilic addition of thiols to acetylene. In a model experiment, the yield of the desired product with the use of heat from carbide hydrolysis was 89%, compared to 30% in this intrinsic heating, which was neglected.

SuFEx-enabled, chemoselective synthesis of triflates, triflamides and triflimidates

Sulfur(vi) Fluoride Exchange (SuFEx) chemistry has emerged as a next-generation click reaction, designed to assemble functional molecules quickly and modularly. Here, we report the ex situ generation of trifluoromethanesulfonyl fluoride (CF₃SO₂F) gas in a two chamber system, and its use as a new SuFEx handle to efficiently synthesize triflates and triflamides. This broadly tolerated protocol lends itself to peptide modification or to telescoping into coupling reactions. Moreover, redesigning the S^VI–F connector with a S Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O → SNR replacement furnished the analogous triflimidoyl fluorides as SuFEx electrophiles, which were engaged in the synthesis of rarely reported triflimidate esters. Notably, experiments showed H₂O to be the key towards achieving chemoselective trifluoromethanesulfonation of phenols vs. amine groups, a phenomenon best explained—using ab initio metadynamics simulations—by a hydrogen bonded termolecular transition state for the CF₃SO₂F triflylation of amines.

Triflyl fluoride gas (CF₃SO₂F) and its aza analogues are reported as new SuFEx activators. These S^VI–F reagents react efficiently with a variety of nucleophiles, yet the presence of water grants complete chemoselectivity to phenols.

Rapid and column-free syntheses of acyl fluorides and peptides using ex situ generated thionyl fluoride

Thionyl fluoride (SOF₂) was first isolated in 1896, but there have been less than 10 subsequent reports of its use as a reagent for organic synthesis. This is partly due to a lack of facile, lab-scale methods for its generation. Herein we report a novel protocol for the ex situ generation of SOF₂ and subsequent demonstration of its ability to access both aliphatic and aromatic acyl fluorides in 55-98% isolated yields under mild conditions and short reaction times. We further demonstrate its aptitude in amino acid couplings, with a one-pot, column-free strategy that affords the corresponding dipeptides in 65-97% isolated yields with minimal to no epimerization. The broad scope allows for a wide range of protecting groups and both natural and unnatural amino acids. Finally, we demonstrated that this new method can be used in sequential liquid phase peptide synthesis (LPPS) to afford tri-, tetra-, penta-, and decapeptides in 14-88% yields without the need for column chromatography. We also demonstrated that this new method is amenable to solid phase peptide synthesis (SPPS), affording di- and pentapeptides in 80-98% yields.

Solvent-free N-Boc deprotection by ex situ generation of hydrogen chloride gas

An efficient, scalable and sustainable method for the quantitative deprotection of the tert-butyl carbamate (N-Boc) protecting group is described, using down to near-stoichiometric amounts of hydrogen chloride gas in solvent-free conditions. We demonstrate the ex situ generation of hydrogen chloride gas from sodium chloride and sulfuric acid in a two-chamber reactor, introducing a straightforward method for controlled and stoichiometric release of HCl gas. The solvent-free conditions allow deprotection of a wide variety of N-Boc derivatives to obtain the hydrochloride salts in quantitative yields. The procedure obviates the need for any work-up or purification steps providing an uncomplicated green alternative to standard methods. Due to the solvent-free, anhydrous conditions, this method shows high tolerance towards acid sensitive functional groups and furnishes expanded functional group orthogonality.

One-Pot and Two-Chamber Methodologies for Using Acetylene Surrogates in the Synthesis of Pyridazines and Their D-Labeled Derivatives

Acetylene surrogates are efficient tools in modern organic chemistry with largely unexplored potential in the construction of heterocyclic cores. Two novel synthetic paths to 3,6-disubstituted pyridazines were proposed using readily available acetylene surrogates through flexible C₂ unit installation procedures in a common reaction space mode (one-pot) and distributed reaction space mode (two-chamber): (1) an interaction of 1,2,4,5-tetrazine and its acceptor-functionalized derivatives with a CaC₂ -H₂ O mixture performed in a two-chamber reactor led to the corresponding pyridazines in quantitative yields; (2) [4+2] cycloaddition of 1,2,4,5-tetrazines to benzyl vinyl ether can be considered a universal synthetic path to a wide range of pyridazines. Replacing water with D₂ O and vinyl ether with its trideuterated analog in the developed procedures, a range of 4,5-dideuteropyridazines of 95-99% deuteration degree was synthesized for the first time. Quantum chemical modeling allowed to quantify the substituent effect in both synthetic pathways.

Carboxyboronate as a Versatile In Situ CO Surrogate in Palladium-Catalyzed Carbonylative Transformations

The application of carboxy-MIDA-boronate (MIDA=N-methyliminodiacetic acid) as an in situ CO surrogate for various palladium-catalyzed transformations is described. Carboxy-MIDA-boronate was previously shown to be a bench-stable boron-containing building block for the synthesis of borylated heterocycles. The present study demonstrates that, in addition to its utility as a precursor to heterocycle synthesis, carboxy-MIDA-boronate is an excellent in situ CO surrogate that is tolerant of reactive functionalities such as amines, alcohols, and carbon-based nucleophiles. Its wide functional-group compatibility is highlighted in the palladium-catalyzed aminocarbonylation, alkoxycarbonylation, carbonylative Sonogashira coupling, and carbonylative Suzuki-Miyaura coupling of aryl halides. A variety of amides, esters, (hetero)aromatic ynones, and bis(hetero)aryl ketones were synthesized in good-to-excellent yields in a one-pot fashion.

Membrane Microreactors for the On-Demand Generation, Separation, and Reaction of Gases

The use of gases as reagents in organic synthesis can be very challenging, particularly at a laboratory scale. This Concept takes into account recent studies to make the case that gases can indeed be efficiently and safely formed from relatively inexpensive commercially available reagents for use in a wide range of organic transformations. In particular, we argue that the exploitation of continuous flow membrane reactors enables the effective separation of the chemistry necessary for gas formation from the chemistry for gas consumption, with these two stages often containing incompatible chemistry. The approach outlined eliminates the need to store and transport excessive amounts of potentially toxic, reactive or explosive gases. The on‐demand generation, separation and reaction of a number of gases, including carbon monoxide, diazomethane, trifluoromethyl diazomethane, hydrogen cyanide, ammonia and formaldehyde, is discussed.

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.