Effect of π-Linkages in Covalent Organic Framework-Catalyzed Light-Harvesting Thioesterification Reaction

Covalent organic frameworks (COFs) serve as an outstanding platform for heterogeneous photocatalysis. We synthesized two analogous pyrene-based two-dimensional COFs with π-conjugated networks, one linked by C═N bonds and the other by C═C bonds, through Schiff base and Knoevenagel condensation reactions, respectively. We investigated the impact of these linkages on the photocatalytic activity of these COFs, using visible-light-mediated thioesterification as a model reaction. It was found that the olefin-linkage COF outperformed the imine-linkage COF as a photocatalyst. The developed protocol demonstrated a broad substrate scope, including 35 diverse carboxylic acids, 14 drug molecules, and several disulfide coupling partners, achieving up to a 95% yield of thioesters. The practical utility of this strategy is further demonstrated by its successful application in gram-scale reactions. The photocatalyst is robust and was successfully reused for multiple cycles without any loss of catalytic activity. The COF backbone facilitated enhanced electron transfer upon light irradiation, enabling the cross-coupling of carboxylic acid and disulfide through a reductive photocatalytic cycle.

Visible-Light-Mediated Synthesis of Thioesters Using Thiocarboxylic Acid as the Dual Reagent

We have developed a visible-light-driven method for thioester synthesis that relies on the unique dual role of thiobenzoic acids as one-electron reducing agents and reactants leading to the formation of sulfur radical species. This synthetic process offers a wide scope, accommodating various thioacid and thiol substrates without the need for a photocatalyst.

Photocatalytic Phosphine-Mediated Thioesterification of Carboxylic Acids with Disulfides

Herein, a practical and effective synthesis of thioesters from readily available carboxylic acids and odorless disulfides was developed under photocatalytic conditions. This approach involves phosphoranyl radical-mediated fragmentation to generate acyl radicals and allows for incorporation of both S atoms of the disulfides into the desired products. In addition to batch reactions, a continuous-flow reactor was employed, enabling rapid thioester synthesis on a gram scale. Preliminary experimental mechanistic studies and the rapid synthesis of dalcetrapib are also demonstrated.

In situ generation of acyloxyphosphoniums for mild and efficient synthesis of thioesters

We present a novel approach for in situ generation of acyloxyphosphoniums by premixing iodobenzene dicarboxylates and triphenylphosphine, resulting in efficient thioester synthesis (up to 100% yield). Stable solid iodobenzene dicarboxylates, achieved via carboxylate exchange, serve as hypervalent iodine precursors. The resulting acyloxyphosphoniums allow convenient one-pot thioester synthesis under mild conditions. Our method demonstrates facile acyloxyphosphonium production from iodobenzene dicarboxylates and Ph3P, enabling diverse thioester preparation. ESI-MS analysis confirms acyloxyphosphonium ion formation, pivotal in acylation. This strategy holds potential for combinatorial thioester synthesis and broader nucleophile modification applications.

Synthesis of Thioesters from Aldehydes via N-Heterocyclic Carbene (NHC) Catalyzed Radical Relay

We have developed an efficient N-heterocyclic carbene (NHC)-catalyzed thioesterification of aldehydes using N-thiosuccinimides as the thiolation reagent. This organocatalyzed transition involves the generation of sulfur radicals by single electron transfer of the Breslow enolate (generated from aldehyde and NHC catalyst) with N-thiosuccinimides. This method offers facile access to various highly functionalized thioesters and exhibits good chemical yields and functional group tolerance.

Photoinduced carbamoylation reactions: unlocking new reactivities towards amide synthesis

The preparation of amide-containing compounds is among the most interesting and challenging topics for the synthetic community. Such relevance is given by their reactive aspects explored in the context of organic synthesis and by the direct application of these compounds as pharmaceuticals and useful materials, and their key roles in biological structures. A simple and straightforward strategy for the amide moiety installation is the use of carbamoyl radicals - this nucleophilic one-electron intermediate is prone to undergo a series of transformations, providing a range of structurally relevant derivatives. In this review, we summarize the latest advances in the field from the perspective of photoinduced protocols. To this end, their synthetic applications are organized accordingly to the nature of the radical precursor (formamides through HAT, 4-substituted-1,4-dihydropyridines, oxamic acids, and N-hydroxyphthalimido esters), the mechanistic aspects also being highlighted. The discussion also includes a recent approach proceeding via photolytic C-S cleavage of dithiocarbamate-carbamoyl intermediates. By exploring fundamental concepts, this material aims to offer an understanding of the topic, which will encourage and facilitate the design of new synthetic strategies applying the carbamoyl radical.

Manganese(III)-promoted thiocarbonylation of alkylborates with disulfides: synthesis of aliphatic thioesters

A Mn(III)-promoted thiocarbonylation procedure toward the synthesis of thioesters has been developed. By employing easily available disulfides and potassium alkyltrifluoroborates as the starting materials, and cheap and non-toxic Mn(OAc)₃·2H₂O as the promotor, a broad range of thioesters were synthesized in good to excellent yields via radical intermediates.

Photocatalytic Activation of Elemental Sulfur Enables a Chemoselective Three-Component Thioesterification

A mild and chemoselective three-component thioesterification using olefins, α-ketoacids, and elemental sulfur has been developed. The photocatalytic activation of elemental sulfur, a cheap and abundant sulfur source, enables the rapid installation of a sulfur atom into molecules, reactions that ordinarily would require the use of reactive and malodorous sulfur-containing compounds such as thiols and thioacids. This novel reaction is characterized by high yields and a broad substrate scope, which enables the introduction of thioester moieties into complex molecules including a steroid, a peptide, and a nonprotected glycoside. Mechanistic studies indicated that the success of this transformation depends on the multiple roles played by the elemental sulfur, including those of a sulfurizing agent, a terminal oxidant, and a HAT mediator.

Nickel-catalyzed carbonylation of thioacetates with aryl iodides via CO insertion and C–S bond cleavage

Aryl thioesters are synthesized via nickel-catalyzed carbonylation of thioacetates with aryl iodides. Alkyl thioacetates undergo coupling with carbon monoxide and aryl iodides to produce the desired aryl thioesters in moderate yields. This catalytic carbonylative coupling process provides a cost-effective and direct approach for the preparation of useful thioesters.

Cu-Catalyzed Oxidative Thioesterification of Aroylhydrazides with Disulfides

An alternative thioesterification reaction via copper-catalyzed oxidative coupling of readily available aroylhydrazides with disulfides is developed, in which oxidative expulsion of N₂ overcomes the activation barrier between the carboxylic acid derivatives and the products. The reaction produces various thioesters in good to excellent yields with good functional group tolerance. In the reaction, stable and easily available aroylhydrazides are used as acyl sources and the relatively odorless disulfides are used as S sources. Mechanistic investigations demonstrate that the reaction of copper salt and oxidant (NH₄)₂S₂O₈ allows for achievement of tandem processes, including deprotonation, free-radical-mediated denitrogenation, and C-S bond formation.

Metal-free electrochemical synthesis of α-ketoamides via decarboxylative coupling of α-keto acids with isocyanides and water

A mild and convenient electrochemical protocol has been developed for the preparation of α-ketoamides via a decarboxylative coupling reaction of α-keto acids with isocyanides and water.

A plausible metal-free ancestral analogue of the Krebs cycle composed entirely of α-ketoacids

Efforts to decipher the prebiotic roots of metabolic pathways have focused on recapitulating modern biological transformations, with metals typically serving in place of cofactors and enzymes. Here we show that the reaction of glyoxylate with pyruvate under mild aqueous conditions produces a series of α-ketoacid analogues of the reductive citric acid cycle without the need for metals or enzyme catalysts. The transformations proceed in the same sequence as the reverse Krebs cycle, resembling a protometabolic pathway, with glyoxylate acting as both the carbon source and reducing agent. Furthermore, the α-ketoacid analogues provide a natural route for the synthesis of amino acids by transamination with glycine, paralleling the extant metabolic mechanisms and obviating the need for metal-catalysed abiotic reductive aminations. This emerging sequence of prebiotic reactions could have set the stage for the advent of increasingly sophisticated pathways operating under catalytic control.

A way to thioacetate esters compatible with non-oxidative prebiotic conditions

The centrality of pyruvate oxidative decarboxylation into acetyl-CoA in current biochemistry is a strong argument for proposing that a similar reaction have been necessary for the development of an effective protometabolism on the primitive Earth. However, such a decarboxylation requires the use of an oxidant and a catalyst, today enzymatic. Based on the mechanisms of the pyruvate dehydrogenase complex and pyruvate-ferredoxin oxidoreductase, we propose that the initial mechanism involved disulfides and occurred via radicals. A first disulfide is obtained by reacting glyoxylate with hydrogen sulfide. It is then possible to produce a wide variety of other disulfides by exchange reactions. When reacted with pyruvate under UV light they give thioesters. This process requires no oxidant and is therefore compatible with what is known of the redox conditions of the early Earth. Neither does it require any catalyst. It could be the first way to acetyl thioesters, a way that was later improved by the introduction of catalysts, first minerals, then enzymes.

Metal-free C–S coupling of thiols and disulfides

A literature overview on C–S coupling reactions using thiols or disulfides as sulfur surrogates under metal-free conditions is presented. Reagents for the transformations include polyvalent iodines, peroxides, tert-butyl nitrite (TBN), DDQ, and aerial oxygen, among others.

Palladium-catalyzed carbonylative transformation of aryl iodides and sulfonyl chlorides: convenient access to thioesters

A palladium-catalyzed carbonylative transformation of aryl iodides and sulfonyl chlorides to thioesters has been studied.

Air-Tolerant Direct Thiol Esterification with Carboxylic Acids Using Hydrosilane via Simple Inorganic Base Catalysis

Direct thioesterification of carboxylic acids with thiols using nontoxic activation agents is highly desirable. Herein, an efficient and practical protocol using safe and inexpensive industrial waste polymethylhydrosiloxane as the activation agent and K₃PO₄ with 18-crown-6 as a catalyst is described. Various functional groups on carboxylic acid and thiol substituents can be tolerated by the present system to afford thioesters in yields of 19-100%.

Thioesters as Acyl Donors in Biocatalytic Friedel-Crafts-type Acylation Catalyzed by Acyltransferase from Pseudomonas Protegens

Functionalization of aromatic compounds by acylation has considerable significance in synthetic organic chemistry. As an alternative to chemical Friedel-Crafts acylation, the C-acyltransferase from Pseudomonas protegens has been found to catalyze C-C bond formation with non-natural resorcinol substrates. Extending the scope of acyl donors, it is now shown that the enzyme is also able to catalyze C-S bond cleavage prior to C-C bond formation, thus aliphatic and aromatic thioesters can be used as acyl donors. It is worth to mention that this reaction can be performed in aqueous buffer. Identifying ethyl thioacetate as the most suitable acetyl donor, the products were obtained with up to >99 % conversion and up to 88 % isolated yield without using additional base additives; this represents a significant advancement to prior protocols.

Metal-free thioesterification of amides generating acyl thioesters

A base-initiated thioesterification of amides with various thiols is reported. This reaction can take place efficiently under metal-free and air-atmospheric conditions, and provides a facile and practically useful approach to the synthesis of valuable acyl thioesters.

Ultrasound-enhanced Ag-catalyzed decarboxylative coupling between α-keto acids and disulfides for the synthesis of thioesters

Herein, we described the ultrasound-assisted synthesis of thioesters via the Ag-catalyzed radical oxidative decarboxylation of α-keto acids, in the presence of disulfides. This protocol takes advantage of the sonication to prepare the title compounds in moderate to very good yields, in only 20 min of reaction. The positive effect of ultrasonic irradiation is attributed to both, the high mass transfer efficiency and to the induced radical formation in the reaction medium.

Efficient synthesis of organic thioacetates in water

Thioacetates as precursors of thiols are interesting starting points for synthesizing other organosulfur compounds. Herein, we propose a simple, efficient and fast method to obtain organic thioacetates using water as a solvent. Taking into account the great attention that has been paid toward environmentally friendly synthetic procedures in the past decades, we prove the role and the strength of the thioacetate anion as a nucleophile for nucleophilic displacement reactions in an aqueous medium. The reactions were carried out under pH control, to prevent the decomposition of the mesylate starting materials, using potassium carbonate as a safe and mild base. A simple work up allows products to be obtained with excellent yield and acceptable purity.

Oxidative Decarboxylation Enables Chemoselective, Racemization-Free Esterification: Coupling of α-Ketoacids and Alcohols Mediated by Hypervalent Iodine(III)

An α-ketoacid could be converted into a reactive acylating agent by treatment with hypervalent iodine(III) species, and in so doing, we discovered a novel decarboxylative acylation of alcohols that affords a variety of esters in excellent yields. The esterification has been applied to a sterol bearing a free carboxylic acid and shows unique chemoselectivity. The procedure is racemization-free and operates under mild conditions.

One-pot synthesis of thioesters with sodium thiosulfate as a sulfur surrogate under transition metal-free conditions

In this paper, we report an efficient synthetic method for thioester formation from sodium thiosulfate pentahydrate, organic halides, and aryl anhydrides. In the one-pot two-step reactions developed in this study, sodium thiosulfate was used as the sulfur surrogate for acylation with anhydrides, followed by substitution with organic halides through the in situ generation of thioaroylate. Furthermore, two important organic compounds could be successfully synthesized using our developed method. The advantages of the one-pot two-step reactions are operational simplicity, structurally diverse products with 42%-90% yields, use of relatively low toxic and odourless reagents, and easy applicability to large-scale operation.

Transition-metal-free KI-catalyzed regioselective sulfenylation of 4-anilinocoumarins using Bunte salts

An efficient and eco-friendly protocol for the KI-catalyzed regioselective sulfenylation of 4-anilinocoumarins with Bunte salts was established under metal-free conditions.

KI-catalyzed oxidative cyclization of α-keto acids and 2-hydrazinopyridines: efficient one-pot synthesis of 1,2,4-triazolo[4,3-a]pyridines

A one-pot approach to 1,2,4-triazolo[4,3-a]pyridines via KI-catalyzed oxidative cyclization was developed with good economical and environmental advantages.

Palladium-catalyzed carbonylation of thioacetates and aryl iodides for the synthesis of S-aryl thioesters

Palladium-catalyzed carbonylation of thioacetates and aryl iodides provided thioesters in good yields.

Silver-catalyzed decarboxylative cascade radical cyclization of tert-carboxylic acids and o-(allyloxy)arylaldehydes towards chroman-4-one derivatives

A convenient silver-catalyzed decarboxylative cascade radical cyclization of tertiary carboxylic acids and o-(allyloxy)arylaldehydes was developed to synthesize 3-alkyl-substituted chroman-4-one derivatives.

Microwave-Assisted Direct Thioesterification of Carboxylic Acids

A one-pot synthesis of thioesters directly from carboxylic acids, N,N'-diphenylthiourea, triethylamine, and primary alkyl halides is described. Microwave-assisted heating and a catalytic amount of 4-(dimethylamino)pyridine (DMAP) further improved the yields. Both aromatic and aliphatic carboxylic acids were converted to the corresponding thioesters, and many functional groups were compatible with this reaction. Several possible reaction intermediates were investigated, and the quaternary ammonium salts, derived from alkyl halides and tertiary amines, were the intermediates to yield thioesters. A new reaction mechanism for this thioesterification is proposed.

Copper-catalyzed oxidative decarboxylative coupling of α-keto acids and sulfoximines

The formation of N-aroylsulfoximines via a copper-catalyzed oxidative decarboxylative coupling of α-keto acids with NH-sulfoximines is reported.

DMSO-promoted regioselective synthesis of sulfenylated pyrazoles via a radical pathway

Highly efficient DMSO-promoted direct sulfenylation of pyrazolones with thiols leading to C-4 sulfenylated pyrazoles has been realized under metal- and solvent-free conditions.

Copper-catalyzed decarboxylative methylthiolation of aromatic carboxylate salts with DMSO

A novel copper-catalyzed decarboxylative methylthiolation of arenecarboxylate salts has been realized using DMSO as the methylthiolation source.