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Synthesis of Formate Esters and Formamides Using an Au/TiO₂-Catalyzed Aerobic Oxidative Coupling of Paraformaldehyde.

ABSTRACT: A simple method for the synthesis of formate esters and formamides is presented based on the Au/TiO₂-catalyzed aerobic oxidative coupling between alcohols or amines and formaldehyde. The suitable form of formaldehyde is paraformaldehyde, as cyclic trimeric 1,3,5-trioxane is inactive. The reaction proceeds via the formation of an intermediate hemiacetal or hemiaminal, respectively, followed by the Au nanoparticle-catalyzed aerobic oxidation of the intermediate. Typically, the oxidative coupling between formaldehyde (2 equiv) and amines occurs quantitatively at room temperature within 4 h, and there is no need to add a base as in analogous coupling reactions. The oxidative coupling between formaldehyde (typically 3 equiv) and alcohols is unprecedented and occurs more slowly, yet in good to excellent yields and selectivity. Minor side-products (2-12%) from the acetalization of formaldehyde by the alcohol are also formed. The catalyst is recyclable and can be reused after a simple filtration in five consecutive runs with a small loss of activity.

SUBMITTER: Metaxas I

PROVIDER: S-EPMC5746930 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Cu-Catalyzed Aerobic Oxidative N-N Coupling of Carbazoles and Diarylamines Including Selective Cross-Coupling.

Project description:A Cu-catalyzed method has been identified for aerobic oxidative dimerization of carbazoles and diarylamines to the corresponding N-N coupled bicarbazoles and tetraarylhydrazines. The reactions proceed under mild conditions (1 atm O2, 60-80 °C) with a catalyst composed of CuBr·dimethylsulfide and N, N-dimethylaminopyridine. Reactions between carbazole and diarylamines show unusually selective cross-coupling, even with a 1:1 ratio of the two substrates. This behavior was found to arise from reversible formation of the tetraarylhydrazine. Formation of this species is kinetically favored, but cleavage of the N-N bond under the reaction conditions leads to selective formation of the thermodynamically favored cross-coupling product.

| S-EPMC6794001 | biostudies-literature

Copper-Catalyzed Oxidative Cross-Coupling of Electron-Deficient Polyfluorophenylboronate Esters with Terminal Alkynes.

Project description:We report herein a mild procedure for the copper-catalyzed oxidative cross-coupling of electron-deficient polyfluorophenylboronate esters with terminal alkynes. This method displays good functional group tolerance and broad substrate scope, generating cross-coupled alkynyl(fluoro)arene products in moderate to excellent yields. Thus, it represents a simple alternative to the conventional Sonogashira reaction.

| S-EPMC7821263 | biostudies-literature

Mechanistic insights into copper-catalyzed aerobic oxidative coupling of N-N bonds.

Project description:Catalytic N-N coupling is a valuable transformation for chemical synthesis and energy conversion. Here, mechanistic studies are presented for two related copper-catalyzed oxidative aerobic N-N coupling reactions, one involving the synthesis of a pharmaceutically relevant triazole and the other relevant to the oxidative conversion of ammonia to hydrazine. Analysis of catalytic and stoichiometric N-N coupling reactions support an "oxidase"-type catalytic mechanism with two redox half-reactions: (1) aerobic oxidation of a CuI catalyst and (2) CuII-promoted N-N coupling. Both reactions feature turnover-limiting oxidation of CuI by O2, and this step is inhibited by the N-H substrate(s). The results highlight the unexpected facility of the N-N coupling step and establish a foundation for development of improved catalysts for these transformations.

| S-EPMC8146583 | biostudies-literature

Unlocking a self-catalytic cycle in a copper-catalyzed aerobic oxidative coupling/cyclization reaction.

Project description:Presented here is a copper-catalyzed, aerobic oxidative C-H/C-H cyclization reaction, which occurs by cleaving the C-H and N-H bonds of 3-phenylindoles. A broad range of 3-phenylindoles can be well tolerated to produce the indole-containing polycyclic aromatic hydrocarbons (PAH) in good to excellent yields. An evaluation of the reaction mechanism is enabled by the isolation of the di- and tri-indole intermediates, highlighting the role of the substrate for this catalytic reaction. The results of these controlled experiments and kinetic studies provide solid experimental support for a self-catalysis reaction, which has rarely been observed in oxidative C-H activation reactions. Additional mechanistic studies indicate that the substrate for this reaction accelerates by the following mechanism: The substrate combines with the Cu catalyst to transform the less active di-indole intermediate into a tri-indole intermediate. This intermediate is quickly converted into the desired product along with regeneration of the substrate copper complex.

| S-EPMC8881718 | biostudies-literature

Practical Synthesis of Amides via Copper/ABNO-Catalyzed Aerobic Oxidative Coupling of Alcohols and Amines.

Project description:A modular Cu/ABNO catalyst system has been identified that enables efficient aerobic oxidative coupling of alcohols and amines to amides. All four permutations of benzylic/aliphatic alcohols and primary/secondary amines are viable in this reaction, enabling broad access to secondary and tertiary amides. The reactions exhibit excellent functional group compatibility and are complete within 30 min-3 h at rt. All components of the catalyst system are commercially available.

| S-EPMC5273591 | biostudies-literature

Pd-Catalyzed Aerobic Oxidative Heck Cross-Coupling for the Straightforward Construction of Indole δ-Lactams.

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| S-EPMC6637253 | biostudies-literature

Mechanistic Insights into the Aerobic Cu(I)-Catalyzed Cross-Coupling of S-Acyl Thiosalicylamide Thiol Esters and Boronic Acids.

Project description:The Density Functional Theory (DFT) method is used to elucidate the nature of the active species and the mechanism of the aerobic CuI-catalyzed cross-coupling of S-acyl thiosalicylamide thiol esters and boronic acids reported previously (J. Am. Chem. Soc.2007, 129, 15734-15735; Angew. Chem., Int. Ed.2009,48, 1417-1421). The energetically lowest isomer of the proposed active species [LC(O)R1]Cu-(O2)-Cu[LC(O)R1]2+, 2a, (where L = thiolatosalicylamide) is found to be I1(OO,OO) with a ?-?2:?2-peroxo Cu2O2-core, while its isomers I2(OO,OO) with a bis-(?-O) Cu2O2-core and I3(OO,OO) with a (?-?1:?1) Cu2O2-core lie only a few kcal/mol higher and separated by 4-7kcal/mol energy barriers. In all these isomers, the thiol ester is coordinated to the Cu-centers via its two O-ends. Isomers with (SO,OO) and (SO,SO) coordination modes of the thiol esters lie slightly higher and are separated with moderate energy barriers. We found the latter isomers to be vital for the reported CuI-templated cross-coupling of S-acyl thiosalicylamide thiol esters and boronic acids under aerobic conditions. The presence of an anion (halide, carboxylate modeled as formate) in the reaction medium is found to be necessary. Its coordination to the active catalyst I1(SO,SO) is the first step of the proposed anion-assisted transmetalation by boronic acid. Overall the transmetalation reaction requires 34.0 kcal/mol and is 24.0 kcal/mol exergonic. This conclusion is in reasonable agreement with available experiments. The C-C bond formation in the transmetalation product requires a 6.3 kcal/mol lower energy barrier and is highly exergonic.

| S-EPMC3615568 | biostudies-literature

Ruthenium catalyzed reductive coupling of paraformaldehyde to trifluoromethyl allenes: CF3-bearing all-carbon quaternary centers.

Project description:Trifluoromethyl substituted allenes engage in ruthenium catalyzed reductive couplings with paraformaldehyde to form products of hydrohydroxymethylation as single regioisomers. This method enables generation of CF3-bearing all-carbon quaternary stereocenters.

| S-EPMC3779475 | biostudies-literature

Pd-catalyzed aerobic oxidative coupling of arenes: evidence for transmetalation between two Pd(II)-aryl intermediates.

Project description:Pd-catalyzed aerobic oxidative coupling of arenes provides efficient access to biaryl compounds. The biaryl product forms via C-H activation of two arenes to afford a Pd(II)ArAr' intermediate, which then undergoes C-C reductive elimination. The key Pd(II)ArAr' intermediate could form via a "monometallic" pathway involving sequential C-H activation at a single Pd(II) center, or via a "bimetallic" pathway involving parallel C-H activation at separate Pd(II) centers, followed by a transmetalation step between two Pd(II)-aryl intermediates. Here, we investigate the oxidative coupling of o-xylene catalyzed by a PdX2/2-fluoropyridine catalyst (X = trifluoroacetate, acetate). Kinetic studies, H/D exchange experiments, and kinetic isotope effects provide clear support for a bimetallic/transmetalation mechanism.

| S-EPMC4161672 | biostudies-literature

A Multifunctional Au/CeO2-Mg(OH)2 Catalyst for One-Pot Aerobic Oxidative Esterification of Aldehydes with Alcohols to Alkyl Esters.

Project description:Au nanoparticles bound to crystalline CeO2 nanograins that were dispersed on the nanoplate-like Mg(OH)2, denoted as Au/CeO2-Mg(OH)2, were developed as the highly active and selective multifunctional heterogeneous catalyst for direct oxidative esterification of aldehydes with alcohols to produce alkyl esters under base-free aerobic conditions using oxygen or air as the green oxidants. Au/CeO2-Mg(OH)2 converted 93.3% of methacrylaldehyde (MACR) to methyl methacrylate (MMA, monomer of poly(methyl methacrylate)) with 98.2% selectivity within 1 h, and was repeatedly used over eight recycle runs without regeneration. The catalyst was extensively applied to other aldehydes and alcohols to produce desirable alkyl esters. Comprehensive characterization analyses revealed that the strong metal-support interaction (SMSI) among the three catalytic components (Au, CeO2, and Mg(OH)2), and the proximity and strong contact between Au/CeO2 and the Mg(OH)2 surface were prominent factors that accelerated the reaction toward a desirable oxidative esterification pathway. During the reaction, MACR was adsorbed on the surface of CeO2-Mg(OH)2, upon which methanol was simultaneously activated for esterifying the adsorbed MACR. Hemiacetal-form intermediate species were subsequently produced and oxidized to MMA on the surface of the electron-rich Au nanoparticles bound to partially reduced CeO2-x with electron-donating properties. The present study provides new insights into the design of SMSI-induced supported-metal-nanoparticles for the development of novel, multifunctional, and heterogeneous catalysts.

| S-EPMC8230364 | biostudies-literature

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