S-Acetylation of Thiols Mediated by Triflic Acid: A Novel Route to Thioesters

Access to thioethers from thiols and alcohols via homogeneous and heterogeneous catalysis

A metal-free dehydrative thioetherification method has been reported, enabling the conversion of various alcohols and thiols into thioethers. By employing triflic acid as a catalyst or utilizing a recyclable NAFION® superacid catalyst, these methods significantly improve the efficiency and practicality of sulfide preparation.

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.

BF3-Mediated Acetylation of Pyrazolo[1,5-a]pyrimidines and Other π-Excedent (N-Hetero)arenes

An operably simple microwave-assisted BF₃-mediated acetylation reaction of pyrazolo[1,5-a]pyrimidines and a plausible mechanism based on density functional theory (DFT) theoretical calculations for this transformation are reported. Remarkably, and to the best of our knowledge, this is the first example of the direct acetylation for the functional pyrazolo[1,5-a]pyrimidine (PP) core. The synthesis of this essential building block is reported in high yields using mild reaction conditions, inexpensive reagents, and even substrates with electron-deficient or highly hindered groups. In addition, one of the new methyl ketones was successfully used as a substrate for producing novel and valuable bis-electrophilic compounds with yields of up to 90%. Notably, the discovered acetylation method was successfully applied in other π-excedent (N-hetero)aromatic substrates.

A Stoichiometric Solvent-Free Protocol for Acetylation Reactions

Considering the remarkable relevance of acetylated derivatives of phenols, alcohols, and aryl and alkyl thiols in different areas of biology, as well as in synthetic organic chemistry, a sustainable solvent-free approach to perform acetylation reactions is proposed here. Acetylation reactions are classically performed using excess of acetic anhydride (Ac₂O) in solvent-free conditions or by eventually working with stoichiometric amounts of Ac₂O in organic solvents; both methods require the addition of basic or acid catalysts to promote the esterification. Therefore, they usually lead to the generation of high amounts of wastes, which sensibly raise the E-factor of the process. With the aim to develop a more sustainable system, a solvent-free, stoichiometric acetylation protocol is, thus, proposed. The naturally occurring phenol, thymol, can be converted to the corresponding—biologically active—ester with good yields, in the presence of 1% of VOSO₄. Interestingly, the process can be efficiently adopted to synthesize other thymyl esters, as well as to perform acetylation of alcohols and aryl and alkyl thiols. Remarkably, a further improvement has been achieved replacing Ac₂O with its greener alternative, isopropenyl acetate (IPA).

Magnetically recyclable silica-coated ferrite magnetite-K10 montmorillonite nanocatalyst and its applications in O, N, and S-acylation reaction under solvent-free conditions

Novel silica-coated ferrite nanoparticles supported with montmorillonite (K₁₀) have been prepared successfully by using a simple impregnation method. Further, these nanoparticles were characterized by using different analytical methods like FT-IR, PXRD, EDS, and FE-SEM techniques. In addition, these nanoparticles have been explored for their catalytic activity for the O, N, and S-acylation reactions under solvent-free conditions which gave moderate to excellent yields in a much shorter reaction time. Moreover, these nanoparticles could easily be separated out from the reaction medium after the reaction completion by using an external magnetic field and have been re-used for 10 cycles without any significant loss of the catalytic activity.

Novel silica-coated ferrite nanoparticles supported with montmorillonite (K₁₀) have been prepared and explored for their catalytic activity for the O, N, and S-acylation reactions under solvent-free conditions.

Visible-Light-Mediated Organocatalyzed Thiol-Ene Reaction Initiated by a Proton-Coupled Electron Transfer

A convenient method for performing a thiol-ene reaction is described. The reaction is performed under blue-light irradiation and catalyzed by photoactive Lewis basic molecules such as acridine orange or naphthalene-fused N-acylbenzimidazole. It is believed that the process is initiated by a proton-coupled electron transfer process within the complex between the thiol and the Lewis basic catalyst.

Copper(ii) triflate-mediated synthesis of functionalized silsesquioxanes via dehydrogenative coupling of POSS silanols with hydrosilanes

In light of the fact that the design of new catalytic routes leading to functionalized silsesquioxanes is currently of high relevance; herein we report a novel, highly effective and convenient catalytic approach for the modification of silsesquioxanes. We present a dehydrogenative coupling reaction of completely as well as incompletely condensed POSS silanols with a wide range of commercially available hydrosilanes mediated by inexpensive copper(ii) trifluoromethanesulfonate. This research also includes mechanistic studies for this process.

In(III) and Hf(IV) Triflate-Catalyzed Hydration and Catalyst-free Hydrohalogenation of Aryl Acetylenes in Liquid Sulfur Dioxide

The use of liquid sulfur dioxide as a reaction solvent to promote chemical transformations of alkynes has been explored. First, a combination of liquid SO₂ and In(OTf)₃ or Hf(OTf)₄ as a catalyst allows to perform hydration of aryl alkynes under mild conditions without a direct addition of Brønsted acid. Second, novel catalyst-free conditions for the synthesis of α-vinyl iodides, bromides, and chlorides from aryl alkynes have been developed in liquid SO₂ using group I and II metal halides and ammonium iodide as the halide ion sources.

Thioester functional polymers

Inspired by the uniqueness and ubiquity of thioesters in nature, much attention has been paid to thioester functionalized materials, yielding applications ranging from responsive polymers to bioconjugates and (bio)degradable polymers.