Combustion-Synthesized Porous CuO-CeO2-SiO2 Composites as Solid Catalysts for the Alkenylation of C(sp3)-H Bonds Adjacent to a Heteroatom via Cross-Dehydrogenative Coupling

A series of mixed oxides of CuO, CeO2, and SiO2 were prepared by gel combustion and employed for the first time as efficient solid catalysts in a solvent-less liquid-phase cross-dehydrogenative coupling. The facile one-pot catalyst synthesis resulted in highly porous materials presenting large specific surface areas and strong metal–support interactions. The interaction with highly dispersed CeO2 enhanced the redox properties of the CuO species. The CuO-CeO2-SiO2 composites exhibited excellent catalytic performance for the selective coupling between 1,1-diphenylethylene and tetrahydrofuran with a yield up to 85% of 2-(2,2-diphenylvinyl)-tetrahydrofuran in the presence of di-tert-butyl peroxide (DTPB) and KI. Albeit both CuO and CeO2 species are proved to be responsible for the catalytic conversion, a great synergistic improvement in the catalytic activity was obtained by extended contact between the oxide phases by high porosity in comparison with the reactions using individual Cu or Ce catalysts. The activity of the composite catalyst was shown to be highly stable after five successive reaction cycles. Furthermore, the study scope was extended to the synthesis of different derivatives via composite-catalyzed coupling of C(sp2)-H with C(sp3-H) adjacent to a heteroatom. The good yields recorded proved the general validity of this composite for the cross-dehydrogenative coupling reaction rarely performed on solid catalysts.

Easy access to secondary and tertiary alcohols via metal-free and light mediated radical carbonyl allylation

Here we report a strategy for carbonyl addition with unactivated alkenes using an organic photocatalyst on both aldehyde and ketone substrates. This protocol grants us a good alternative to the traditional Barbier-Grignard allylation that exhibits poor functional group tolerance. With this method the stoichiometric use of metals can be avoided, high atom economy can be achieved and fewer by-products are generated.

Photoredox Generation of N-Centered Hydrazonyl Radicals Enables the Construction of Dihydropyrazole-Fused gem-Difluoroalkenes

An efficient visible-light-promoted N-radical-mediated tandem radical cyclization/defluorinated alkylation of β,γ-unsaturated hydrazones, and α-trifluoromethyl alkenes is described. This protocol provides a general and effective route to synthesize various dihydropyrazole-fused gem-difluoroalkenes at moderate to excellent yields under redox-neutral, metal-free, and mild conditions.

Solvent-free synthesis of propargylamines: an overview

Propargylamines are a class of compounds with many pharmaceutical and biological properties. A green approach to synthesize such compounds is very relevant. This review aims to describe the solvent-free synthetic approaches towards propargylamines via A3 and KA2 coupling reactions covering the literature up to 2021.

Direct functionalization of cyclic ethers with maleimide iodides via free radial-mediated sp3 C-H activation

Cyclic ethers are important scaffolds employed in the synthesis of various natural products and pharmaceutical ingredients. A novel free radical-initiated reaction between cyclic ethers and maleimide iodides through C-H activation is developed, avoiding the use of transition metallic catalysts. This method provides a simple approach to derive cyclic ethers, which were further applied in various cross coupling reactions.

"One-Pot" Synthesis of γ-Pyrones from Aromatic Ketones/Heteroarenes and Carboxylic Acids

Despite the various attractive properties of γ-pyrones, there are still some deficiencies in their synthetic approaches such as lower atom economy, multistep processes, and prefunctionalization of the reagents. In this work, an efficient and simple (CF₃CO)₂O/CF₃SO₃H-mediated "one-pot" approach was realized to produce γ-pyrones by applying aromatic ketones/heteroarenes and carboxylic acids as the starting materials. The target products were isolated in moderate to excellent yields. The reaction mechanism was studied by density functional theory calculational methods. The results of experimental and theoretical investigations not only helped us explain the reason of high selectivity formation of β-diketones but also proved that 1,3,5-ketones might be important intermediates for the cyclization to afford γ-pyrones.

Eosin Y-Catalyzed Synthesis of 3-Aminoimidazo[1,2-a]Pyridines via the HAT Process under Visible Light through Formation of the C-N Bond

A comfortable, environment-friendly, and metal-free approach for synthesizing the biologically important moiety aminoimidazopyridine through the multicomponent reaction of benzylamine, 2-aminopyridine, and t-butyl isocyanide under visible light using eosin Y as a photocatalyst has been developed. Inexpensive, nontoxic, the effortless accessibility of starting materials, and nonparticipation of particular glassware and a photoreactor system are important qualities of the current approach. Strangely, the mild conditions, environment-friendly, and enumerating tolerance of an extensive range of both electron-donating and electron-withdrawing groups are additional features of the approach.

Optimization of a Decatungstate-Catalyzed C(sp3)-H Alkylation Using a Continuous Oscillatory Millistructured Photoreactor

Tetrabutylammonium decatungstate (TBADT) has emerged as an efficient and versatile photocatalyst for hydrogen atom transfer (HAT) processes that enables the cleavage of both activated and unactivated aliphatic C-H bonds. Using a recently developed oscillatory millistructured continuous-flow photoreactor, investigations of a decatungstate-catalyzed C(sp³)-H alkylation protocol were carried out, and the results are presented here. The performance of the reactor was evaluated in correlation to several chemical and process parameters, including residence time, light intensity, catalyst loading, and substrate/reagent concentration. In comparison with previously reported batch and flow protocols, conditions were found that led to considerably higher productivity, achieving a throughput up to 36.7 mmol/h with a residence time of only 7.5 min.

Visible-light-induced [4 + 2] cycloaddition of pentafulvenes by organic photoredox catalysis

We have developed thioxanthylium photoredox catalyzed [4 + 2] cycloaddition of pentafulvenes at room temperature under green light irradiation, which affords tetrahydrocyclopenta[b]chromenes with high regioselectivities. The present reaction provides a sustainable approach to carry out the cycloaddition of pentafulvenes without the use of transition metal catalysts or high-temperature conditions. This procedure enables a mild and straightforward access to 1,3a,9,9a-tetrahydrocyclopenta[b]chromenes. The quantum yield of the reaction (Φ = 0.15) indicates that the reaction would mainly proceed via photocatalytic pathways.

A visible-light-induced “on–off” one-pot synthesis of 3-arylacetylene coumarins with AIE properties

A mild one-pot approach to 3-arylacetylene coumarins with potential AIE activities was developed via photosensitizer-free photocatalysis and thermocatalysis.

IrIII-Catalyzed direct syntheses of amides and esters using nitriles as acid equivalents: a photochemical pathway

An unprecedented Ir^III[df(CF₃)ppy]₂(dtbbpy)PF₆-catalyzed simple photochemical process for direct addition of amines and alcohols to the relatively less reactive nitrile triple bond is described herein.

Direct photochemical cross-coupling between aliphatic acids and BF3K salts

We describe a novel photoredox hetero-coupling reaction of two C (sp³) radicals from aliphatic acids or BF₃K salts.

Rhodium(iii)-catalyzed unreactive C(sp3)-H alkenylation of N-alkyl-1H-pyrazoles with alkynes

The first example of pyrazole-directed rhodium(iii)-catalyzed unreactive C(sp³)-H alkenylation with alkynes has been described, which showed a relatively broad substrate scope with good functional group compatibility. Moreover, we demonstrated that the transitive coordinating center pyrazole could be easily removed under mild conditions.

Copper(i)-catalyzed benzylation of triazolopyridine through direct C-H functionalization

A general and efficient copper-catalyzed benzylation reaction of triazolopyridine with N-tosylhydrazones was developed. This reaction forms a C(sp²)-C(sp³) bond through cross-coupling, and represents an exceedingly practical method to afford 3-benzylated triazolopyridines in moderate to good yields. A proposed mechanistic pathway underlying this reaction was outlined. This catalytic transformation should enable broad synthetic applications in functionalization chemistry, allowing the synthesis of new pharmaceutically relevant triazolopyridine derivatives.