Tetrabutylammonium Decatungstate Research Articles

Selective Oxidation of Alcohols to Carbonyls Under Decatungstate-Mediated Photoelectrochemical Conditions.

The oxidation of alcohols to the corresponding carbonyl derivatives has been realized under photoelectrochemical conditions in the presence of tetrabutylammonium decatungstate (TBADT) as the homogeneous photocatalyst. The protocol can be applied to both primary and secondary, benzylic and aliphatic alcohols. The desired products are obtained selectively, skipping the need for purposely added chemical oxidants. An in-depth study of photoelectrochemical conditions revealed that the protocol works best under amperostatic conditions in an undivided electrochemical cell irradiated with a 390 nm LED lamp. The comparison with analogous electrochemical and chemical oxidant-promoted photocatalytic transformations demonstrates the superior efficiency and selectivity of the hereby reported photoelectrochemical conditions.

Photocatalyzed Direct C(sp3)-H Alkenylation of Unactivated Alkanes via Tandem C-C Activation of Cyclopropenes.

A highly adaptable method has been developed for the alkenylation of a broad spectrum of inert alkanes, employing milder reaction conditions. Tetrabutylammonium decatungstate (TBADT) serves as a photocatalyst for hydrogen atom transfer (HAT), instigating the formation of transient alkyl radicals through C(sp3)-H functionalization. These radicals exhibit regioselective addition to cyclopropenes, followed by the subsequent activation of C-C bonds, forming the corresponding vinylated derivatives. This methodology accommodates diverse unreactive C(sp3)-H bond motifs and multisubstituted cyclopropenes, enabling the efficient synthesis of highly functionalized olefins with high diastereoselectivity.

Visible light-driven decarboxylative alkylation of azomethine imines with carboxylic acids

The alkylation of cyclic five-membered azomethine imines with carboxylic acids proceeds under irradiation with 400 nm light using a dual catalytic system consisting of 9-arylacridine and tetrabutylammonium decatungstate. Azomethine imines containing aromatic, heterocyclic and aliphatic groups are suitable for the process providing pyrazolidin-3-ones in 42–98% yields.

Photocatalytic Asymmetric Acyl Radical Truce–Smiles Rearrangement for the Synthesis of Enantioenriched α‐Aryl Amides

AbstractThe radical Truce–Smiles rearrangement is a straightforward strategy for incorporating aryl groups into organic molecules for which asymmetric processes remains rare. By employing a readily available and non‐expensive chiral auxiliary, we developed a highly efficient asymmetric photocatalytic acyl and alkyl radical Truce–Smiles rearrangement of α‐substituted acrylamides using tetrabutylammonium decatungstate (TBADT) as a hydrogen atom–transfer photocatalyst, along with aldehydes or C−H containing precursors. The rearranged products exhibited excellent diastereoselectivities (7 : 1 to >98 : 2 d.r.) and chiral auxiliary was easily removed. Mechanistic studies allowed understanding the transformation in which density functional theory (DFT) calculations provided insights into the stereochemistry‐determining step.

Photocatalytic Asymmetric Acyl Radical Truce-Smiles Rearrangement for the Synthesis of Enantioenriched α-Aryl Amides.

The radical Truce-Smiles rearrangement is a straightforward strategy for incorporating aryl groups into organic molecules for which asymmetric processes remains rare. By employing a readily available and non-expensive chiral auxiliary, we developed a highly efficient asymmetric photocatalytic acyl and alkyl radical Truce-Smiles rearrangement of α-substituted acrylamides using tetrabutylammonium decatungstate (TBADT) as a hydrogen atom-transfer photocatalyst, along with aldehydes or C-H containing precursors. The rearranged products exhibited excellent diastereoselectivities (7 : 1 to >98 : 2 d.r.) and chiral auxiliary was easily removed. Mechanistic studies allowed understanding the transformation in which density functional theory (DFT) calculations provided insights into the stereochemistry-determining step.

Direct C(sp3)-H functionalization with thiosulfonates via photoredox catalysis

While C(sp3)-S bonds exist in many biologically active compounds, the direct catalytic C(sp3)-H thiolation remains elusive. Herein, we report a convenient and green C(sp3)-H thiolation approach mediated by using tetrabutylammonium decatungstate (TBADT) as a hydrogen atom transfer (HAT) photocatalyst. A wide range of C(sp3)-H bond-containing etheric, allylic, alkyl, ketonic, amidic substrates and sulfonyl-based SOMOphiles participated in the reaction, producing thioethers with high efficiency. The present protocol features green characteristics, such as being free of harmful oxidants and additives; step-economic; redox-neutral; and amenable to scale-up assisted by continuous-flow technology.

C(sp3)-C(sp3) Coupling of Cycloalkanes and Alkyl Halides via Dual Photocatalytic Hydrogen Atom Transfer and Nickel Catalysis.

Functionalization of C(sp3)-H bonds represents the most straightforward and atom-economical transformation in organic synthesis. An innovative approach integrating photocatalytic hydrogen atom transfer (HAT) and transition metal catalysis has made significant progress in the coupling of α-heterosubstituted C-H bonds with alkyl halides. However, unactivated alkanes were ineffective as a result of the preponderance of byproduct formation. Herein, we demonstrate direct HAT and nickel catalysis in the coupling of cycloalkanes and benzyl bromides/primary alkyl iodides. Additionally, tetrabutylammonium decatungstate (TBADT) was recovered and recycled.

Dual Acridine/Decatungstate Photocatalysis for the Decarboxylative Radical Addition of Carboxylic Acids to Azomethines.

A concept for the dual use of acridine and tetrabutylammonium decatungstate photocatalysts in the reactions of carboxylic acids is proposed. Imines generated in situ from aldehydes and p-methoxyaniline, as well as other azomethines, were used as radical acceptors. The role of the decatungstate is believed to facilitate the turnover of the acridine photocatalyst by means of hydrogen atom transfer.

Decatungstate‐Catalyzed Carbon‐Carbon Bond Formation Between Furfural and Electron‐Deficient Olefins

AbstractFurfural is produced on a large commercial scale from lignocellulose and can be used for the preparation of several industrial chemicals with four to five carbon atoms. Further functionalization of furfural by C−H activation, however, is less widely developed. In the present work, tetrabutylammonium decatungstate is investigated as an inexpensive photocatalyst for activating the aldehyde C−H bond and mediate a coupling between furfural and electron‐deficient olefins. The results show that furfural can be successfully added to benzylidene malononitriles, acrylates, itaconic anhydride, maleic anhydride, 2‐vinylpyridine and phenyl vinyl sulfone to generate the corresponding furanyl ketones in moderate‐to‐good yields. The electronic properties of the electron‐deficient olefins are instrumental for achieving a favorable reaction with furfural. The findings show how photocatalysis can be used to form new carbon‐carbon bonds from a platform molecule, which in this way can be converted into a number of more advanced structures.

Sustainable Photocatalytic Acylation of Transition Metal Dichalcogenides with Atom Economy.

Transition metal dichalcogenides (TMDs) are promising 2D nanomaterials for diverse applications, but their intrinsic chemical inertness hinders their modification. Herein, a novel approach is presented for the photocatalytic acylation of 2H-MoS2 and 2H-MoSe2, utilizing tetrabutyl ammonium decatungstate ((nBu4N)4W10O32) polyoxometalate complex as a catalyst and a conventional halogen lamp as a source of irradiation. By harnessing the semiconducting properties of TMDs, new avenues emerge for the functionalization of these materials. This novel photocatalytic protocol constitutes the first report on the chemical modification of 2D nanomaterials based on a catalytic protocol and applies to both aliphatic and aromatic substrates. The scope of the decatungstate-photocatalyzed acylation reaction of TMDs is explored by employing an alkyl and an aromatic aldehyde and the success of the methodology is confirmed by diverse spectroscopic, thermal, microscopy imaging, and redox techniques. This catalytic approach on modifying 2D nanomaterials introduces the principles of atom economy in a functionalization protocol for TMDs. It marks a transformative shift toward more sustainable and efficient methodologies in the realm of TMD modification and nanomaterial chemistry.

Chemical Catalysis Guides Structural Identification for the Major In Vivo Metabolite of the BET Inhibitor JQ1.

The bromodomain inhibitor (+)-JQ1 is a highly validated chemical probe; however, it exhibits poor in vivo pharmacokinetics. To guide efforts toward improving its pharmacological properties, we identified the (+)-JQ1 primary metabolite using chemical catalysis methods. Treatment of (+)-JQ1 with tetrabutylammonium decatungstate under photochemical conditions resulted in selective formation of an aldehyde at the 2-position of the thiophene ring [(+)-JQ1-CHO], which was further reduced to the 2-hydroxymethyl analog [(+)-JQ1-OH]. Comparative LC/MS analysis of (+)-JQ1-OH to the product obtained from liver microsomes suggested (+)-JQ1-OH as the major metabolite of (+)-JQ1. The 2-thienyl position was then substituted to generate a trideuterated (-CD3, (+)-JQ1-D) analog having half-lives that were 1.8- and 2.8-fold longer in mouse and human liver microsomes, respectively. This result unambiguously confirmed (+)-JQ1-OH as the major metabolite of (+)-JQ1. These studies demonstrate an efficient process for studying drug metabolism and identifying the metabolic soft spots of bioactive compounds.

Tetrabutylammonium decatungstate (TBADT), a compelling and trailblazing catalyst for visible-light-induced organic photocatalysis.

Tetrabutylammonium decatungstate (TBADT) has recently emerged as an intriguing photocatalyst under visible-light or near-visible-light irradiation in a wide range of organic reactions that were previously not conceivable. Given its ability to absorb visible light and excellent effectiveness in activating unactivated chemical bonds, it is a promising addition to traditional photocatalysts. This review covers some of the contemporary developments in visible-light or near-visible-light photocatalysis reactions enabled by the TBADT catalyst to 2023, with the contents organized by reaction type.

Decatungstate-photocatalyzed direct acylation of N-heterocycles with aldehydes

A novel photocatalytic acylation strategy was developed harnessing tetrabutylammonium decatungstate (TBADT) as a hydrogen atom transfer (HAT) photocatalyst to facilitate the direct coupling of aldehydes with N-heterocycles at ambient temperature.

Ring‐Opening Coupling Reaction of Cyclopropanols with Electrophilic Alkenes Enabled by Decatungstate as Photoredox Catalyst

AbstractWe introduce a methodology for the photocatalytic generation of β‐ketoalkyl radicals from tertiary cyclopropanols, utilizing tetrabutylammonium decatungstate (TBADT) as a photoredox catalyst. The application is demonstrated by the synthesis of distantly functionalized ketones via the redox‐neutral addition of the cyclopropanol‐derived β‐ketoalkyl radicals to the double bond of electrophilic olefins. The transformation occurs under ambient temperature conditions and is suitable for coupling a wide range of cyclopropanol and alkene substrates. This was demonstrated by the preparation of 33 ketone products with 35–92% yield. The method's preparative robustness has been validated through upscaled preparations conducted under continuous flow conditions. Mechanistic investigations support the role of TBADT as a photoredox catalyst, which facilitates the single electron oxidation of cyclopropanols, followed by the electron transfer from the reduced form of decatungstate to the electrophilic double bond of alkene. Moreover, we found that electron‐rich aromatic cyclopropanols and electron‐deficient olefins form photoactive electron donor‐acceptor (EDA) complexes. This property allows the reaction to proceed under UV light irradiation via the photoinduced charge transfer in the absence of the photocatalyst.

Photocatalyzed Carbon−Carbon Bond Formation Between Glycerol and Electron‐Deficient Olefins

AbstractGlycerol is produced in large quantities as a co‐product in the manufacturing of biodiesel and has received relatively little attention as a substrate for carbon−carbon bond‐forming reactions. In this work, the photocatalyzed reaction between glycerol and electron‐deficient olefins is investigated to regioselectively insert an alkyl group at C2 in the triol. The results show that the transformation is highly dependent on the nature of the photocatalyst and the olefin. In the presence of an iridium catalyst and quinuclidine, glycerol can be coupled at C2 with sterically unhindered acrylates. In the presence of tetrabutylammonium decatungstate, glycerol can be reacted with fumaronitrile, N‐methyl maleimide, methyl acrylate and itaconic anhydride where the latter two substrates require the additional presence of potassium persulfate as an oxidant. These findings give rise to several new carbon−carbon bond‐forming reactions with glycerol that allow the triol to be converted into more elaborate structures.

Site‐Selective Direct Intermolecular C(sp3)−H Alkylation of Saccharides and Switching of Reaction Sites by Changing Photocatalysts

AbstractWe developed a site‐selective intermolecular C(sp3)−H alkylation of saccharides with electron‐deficient alkenes using photocatalysis by anthraquinone and tetrabutylammonium decatungstate (TBADT). The main reaction site of anthraquinone‐catalyzed C(sp3)−H alkylation is determined by the weakness of the C−H bond. The reaction site can be switched by changing the photocatalyst to TBADT, and the site‐selectivity is controlled by the steric hindrance between the bulkier TBADT photocatalyst and the substituents of the saccharides. The reaction is compatible with several electron‐deficient alkenes and saccharides, and provides C‐saccharides in good yields. Furthermore, the monoalkylated product was obtained in excellent yield, even on the gram scale, under TBADT photocatalysis. Applicability was demonstrated by site‐selective C(sp3)−H alkylation of glycosyl derivatives. The reactions proceed via a site‐selective hydrogen atom transfer between the photocatalyst and saccharide, and the generated carbon radical reacts with an electron‐deficient alkene to give alkylated products.

Decatungstate‐Photocatalyzed Functionalization of α‐Imino Esters for the Preparation of Unnatural α‐Amino Acid Derivatives

AbstractA library of unnatural α‐amino acid derivatives has been prepared via the hydrofunctionalization of the C=N bond in a set of compounds belonging to the family of α‐imino esters. The devised methodology capitalizes on the use of tetrabutylammonium decatungstate as the photocatalyst to generate C‐centered radicals from aliphatic and aromatic aldehydes, cyclic and acyclic oxygenated compounds and even cycloalkanes, via a hydrogen atom transfer (HAT) step. The best performance was observed when α‐hydrazono esters were employed in the role of radical traps, which delivered the corresponding (protected) α‐hydrazino acids as products. The versatility of the protocol was further demonstrated by the possibility to functionalize the herbicide safener isoxadifen‐ethyl.

One-step photocatalyzed functionalization of [60]Fullerene: A study on the direct incorporation of amides and lactams to C60

A direct, selective functionalization of C60 with amides and lactams has been developed. This efficient photochemical approach utilizes a diverse variety of radicals deriving from secondary and tertiary carboxy-, sulfonyl-, phosphoramides as well as lactams through a hydrogen atom transfer (HAT) process mediated by tetrabutylammonium decatungstate [(n-Bu4N)4W10O32]. The single addition of these carbon-centered radicals to [60]fullerene proceeded smoothly to produce a novel class of previously unexplored fullerene-based materials. Important structural insight, such as the rotational energy barrier of the amide C(O)–N bond, for these nanostructures is provided and has been experimentally determined by the use of Dynamic NMR spectroscopy. A mechanism for this new reaction has been proposed based mainly on the structure of reaction products and kinetic H/D isotope effect studies.

Synthesis of Linear Enamides and Enecarbamates via Photoredox Acceptorless Dehydrogenation

AbstractIn recent years, several methods for the direct desaturation of aliphatic compounds have been developed, facilitated by the unique combination of photoredox and transition‐metal catalysis. Hereby, alkenes with high functionalization potential can be prepared in a straightforward fashion. We adapted a previously reported system involving tetrabutylammonium decatungstate (TBADT) as hydrogen atom transfer (HAT) agent and a cobaloxime co‐catalyst for dihydrogen evolution for the dehydrogenative preparation of linear enamides and enecarbamates from saturated precursors. The substrate scope includes several natural products and drug derivatives. The reaction does not require noble metal catalysts, exhibits short reaction times compared to previous methods and is suitable for the late‐stage functionalization of drug derivatives.magnified image

TBADT‐Mediated C‐C Bond Formation Exploiting Aryl Aldehydes in a Photochemical Flow Reactor

AbstractA robust and general photochemical process is reported converting various aryl aldehydes into β‐ketonitriles and related species. Tetrabutylammonium decatungstate (TBADT) is used as photocatalyst in combination with a high‐power LED emitting at 365 nm. Standardization and scalability are enabled by using a flow reactor platform integrating the LED light source placed within an encased reactor coil. Under optimized conditions a variety of aromatic and heteroaromatic aldehydes is reacted with acrylonitrile, methyl methacrylate and phenyl vinyl sulfone to give the desired products in high yields, short residence times of 5–30 minutes and a throughput of up to 41 mmol/h. This continuous process overcomes limitations previously encountered for aromatic substrates and represents an effective means to generate a variety of difunctionalized building blocks for further elaborations with an ideal atom economy.