Heterogeneous Titania-Photoredox/Nickel Dual Catalysis: Decarboxylative Cross-Coupling of Carboxylic Acids with Aryl Iodides

Cu-Catalyzed decarboxylative annulation of N-substituted glycines with 3-formylchromones: synthesis of functionalized chromeno[2,3-b]pyrrol-4(1H)-ones

A novel protocol was developed for preparing functionalized chromeno[2,3-b]pyrrol-4(1H)-ones 3 (CMPOs) from 3-formylchromones with N-substituted glycine derivatives. The method entailed decarboxylative annulation of the acyl group of 3-formylchromones by simply heating a mixture of substrates 1-2 and toluene oxidized by 2-di-tert-butyl peroxide (DTBP) and catalyzed by CuBr. As a result, a series of CMPOs 3 were produced via a cascade reaction. This protocol can be used to synthesize functionalized CMPOs via combinatorial and parallel syntheses in a one-pot reaction rather than a tedious multi-step reaction.

Visible-light-induced cross-coupling of aryl iodides with hydrazones via an EDA-complex

A visible-light-induced, transition-metal and photosensitizer-free cross-coupling of aryl iodides with hydrazones was developed. In this strategy, hydrazones were used as alternatives to organometallic reagents, in the absence of a transition metal or an external photosensitizer, making this cross-coupling mild and green. The protocol was compatible with a variety of functionalities, including methyl, methoxy, trifluoromethyl, halogen, and heteroaromatic rings. Mechanistic investigations showed that the association of the hydrazone anion with aryl halides formed an electron donor–acceptor complex, which when excited with visible light generated an aryl radical via single-electron transfer.

Visible-light-induced catalyst-free cross-coupling of aryl iodides with hydrazones via single-electron-transfer was reported. The mechanistic investigations showed that the association of hydrazone anion with aryl iodides formed an EDA complex.

Au–Pd@ZnO alloy nanoparticles: a promising heterogeneous photocatalyst toward decarboxylative trifluoromethylation under visible-light irradiation

Au–Pd@ZnO alloy nanoparticles have promising potential as heterogeneous photocatalysts for decarboxylative trifluoromethylation reactions under visible light irradiation.

Development of a Fluorescent Nanofibrous Template by In Situ SNAr Polymerization of Fluorine-Containing Terphenyls with Aliphatic Diols: Self-Assembly and Optical and Liquid Crystal Properties

Stimulus-responsive supramolecular organogels have been broadly studied, but the assembly of a liquid crystalline organogel with a thermoreversible response remains a challenge. This could be attributed to the difficulty of designing organogelators with liquid crystalline properties. Nucleophilic aromatic substitution (S_NAr) has been utilized to produce a diversity of pentafluorobenzene-containing aromatics, which are very regioselective to para positions. Those pentafluorobenzene-functionalized aromatics have been ideal compounds for the preparation of calamitic liquid crystals. In this context, novel fluoroterphenyl-containing main-chain polyether (FTP@PE) was synthesized using in situ S_NAr polymerization as a convenient and effective synthetic strategy toward the development of fluorescent liquid crystals bearing fluoroterphenyl and ether groups. The fluoroterphenyl unit was synthesized by Cu(I)-supported decarboxylation cross-coupling of potassium pentafluorobenzoate and 1,4-diiodobenzene. The chemical structures of FTP@PE were studied with ¹H/¹³C/¹⁹F nuclear magnetic resonance and infrared spectra. The liquid crystal mesophases were determined with differential scanning calorimetry and polarizing optical microscopy. Ultraviolet-visible absorbance and emission spectral profiles showed solvatochromic activity. The nanofibrous morphologies were studied with a scanning electron microscope. The organogels of FTP@PE were developed in a number of solvents via van der Waals attraction forces of aliphatic moieties and π stacking of fluoroterphenyl groups. They demonstrated thermoreversible responsiveness.

Visible-light-mediated semi-heterogeneous black TiO2/nickel dual catalytic C (sp2)-P bond formation toward aryl phosphonates

The combination of black TiO₂ nanoparticles (NPs) with a nickel catalyst provides a low-cost, sustainable, and reusable alternative dual catalytic system to a homogeneous counterpart (noble metals). This black TiO₂-photoredox/nickel dual catalytic system has efficiently driven C-P bond formation between aryl iodides and diarylphosphine oxides under visible light, providing good to excellent yields as well as tolerating a variety of functional groups. The practical application of this semi-heterogeneous protocol has been highlighted by a sunlight experiment, a gram-scale reaction, and a reusability test.

Nickel-Catalyzed Decarboxylative Alkenylation of Anhydrides with Vinyl Triflates or Halides

Decarboxylative cross-coupling of aliphatic acid anhydrides with vinyl triflates or halides was accomplished via nickel catalysis. This methodology works well with a broad array of substrates and features abundant functional group tolerance. Notably, our approach addresses the issue of safe and environmental installation of methyl or ethyl group into molecular scaffolds. The method possesses high chemoselectivity toward alkyl groups when aliphatic/aromatic mixed anhydrides are involved. Furthermore, diverse ketones could be modified with our strategy.

A Low-Cost, Well-Designed Catalytic System Derived from Household Waste "Egg Shell": Applications in Organic Transformations

A waste feedstock-derived economical basic alternative catalyst is described in this review. Eggshell is one of the household wastes created in tons of weight daily. Therefore, in order to reduce the environmental pollution-related problems, its use in heterogeneous catalysis can be attributed as a great contribution for the chemical and material science society to carry out several known reactions and for the much-needed energy alternative biodiesel production as low-cost catalytic system. Keeping green chemistry in mind, industrial use of these catalysts may also reduce the use of other traditionally used high-cost chemical catalytic systems.

sp3 C-H Arylation and Alkylation Enabled by the Synergy of Triplet Excited Ketones and Nickel Catalysts

Triplet ketone sensitizers are of central importance within the realm of photochemical transformations. Although the radical-type character of triplet excited states of diaryl ketones suggests the viability for triggering hydrogen-atom transfer (HAT) and single-electron transfer (SET) processes, among others, their use as multifaceted catalysts in C-C bond-formation via sp³ C-H functionalization of alkane feedstocks still remains rather unexplored. Herein, we unlock a modular photochemical platform for forging C( sp³)-C( sp²) and C( sp³)-C( sp³) linkages from abundant alkane sp³ C-H bonds as functional handles using the synergy between nickel catalysts and simple, cheap and modular diaryl ketones. This method is distinguished by its wide scope that is obtained from cheap catalysts and starting precursors, thus complementing existing inner-sphere C-H functionalization protocols or recent photoredox scenarios based on iridium polypyridyl complexes. Additionally, such a platform provides a new strategy for streamlining the synthesis of complex molecules with high levels of predictable site-selectivity and preparative utility. Mechanistic experiments suggest that sp³ C-H abstraction occurs via HAT from the ketone triplet excited state. We believe this study will contribute to a more systematic utilization of triplet excited ketones as catalysts in metallaphotoredox scenarios.

Visible-Light-Driven Decarboxylative Alkylation of C-H Bond Catalyzed by Dye-Sensitized Semiconductor

A decarboxylative alkylation of benzylic C(sp³)-H bonds of N-aryl tetrahydroisoquinolines under the irradiation of blue light is reported, featuring a broad substrate scope, low cost, heavy-metal-free, and mild conditions. A preliminary mechanistic study indicated that radical intermediates are involved during the course of the reaction.

N-Alkylation of functionalized amines with alcohols using a copper-gold mixed photocatalytic system

Direct functionalization of amino groups in complex organic molecules is one of the most important key technologies in modern organic synthesis, especially in the synthesis of bio-active chemicals and pharmaceuticals. Whereas numerous chemical reactions of amines have been developed to date, a selective, practical method for functionalizing complex amines is still highly demanded. Here we report the first late-stage N-alkylation of pharmaceutically relevant amines with alcohols at ambient temperature. This reaction was achieved by devising a mixed heterogeneous photocatalyst in situ prepared from Cu/TiO₂ and Au/TiO₂. The mixed photocatalytic system enabled the rapid N-alkylation of pharmaceutically relevant molecules, the selective mono- and di-alkylation of primary amines, and the non-symmetrical dialkylation of primary amines to hetero-substituted tertiary amines.

Photo-induced thiol coupling and C–H activation using nanocrystalline lead-halide perovskite catalysts

Cesium lead halide perovskite nanocrystals have been the first time utilized as photocatalysts for organic bond formations.

TiO2 photocatalysis for C–C bond formation

Synergistic utilization of TiO₂-photo-generated holes and electrons is a potential protocol for catalytic C–C bond formation reactions.

Decarboxylative formylation of aryl halides with glyoxylic acid by merging organophotoredox with palladium catalysis

Decarboxylative formylation of aryl halides with glyoxylic acid enabled by combining organophotoredox with palladium catalysis.

Atom-Transfer Radical Addition to Unactivated Alkenes by using Heterogeneous Visible-Light Photocatalysis

Heterogeneous visible-light photocatalysis represents an important route toward the development of sustainable organic synthesis. In this study visible light-induced, heavy metal-free atom-transfer radical addition to unactivated terminal olefins is carried out by using the combination of heterogeneous titanium dioxide as photocatalyst and a hypervalent iodine(III) reagent as co-initiator. The reaction can be applied to a range of substrates with good functional-group tolerance under very mild conditions. In addition to a number of commonly used atom-transfer reagents, the relatively challenging chloroform is also suitable.

Photocatalytic Dehydrogenation of Primary Alcohols: Selectivity Goes against Adsorptivity

Solid/liquid heterogeneous photocatalysis was often considered to occur on the active sites of a solid catalyst surface. Herein, we report that the selectivity of photocatalytic dehydrogenative oxidations of aliphatic primary alcohols in acetonitrile solution into corresponding aldehydes exhibits an anomalous relationship with adsorption behavior of the alcohols. By using Pt-loaded TiO₂ photocatalyst in an inert atmosphere under UV light illumination, primary short-chain alcohols (SCAs) with strong adsorption were dehydrogenated into aldehydes in very poor selectivity, whereas weak-adsorbable long-chain alcohols (LCAs) were transformed into corresponding aldehydes with much higher selectivity. More than 20 examples of primary LCAs (C₄-C₁₀) were successfully transformed into their corresponding aldehydes with satisfactory selectivity and yield. Both solid-state magic-angle-spinning ¹³C NMR and attenuated total reflectance-Fourier transform infrared spectroscopy studies provided concrete differences in adsorption behaviors on the Pt-TiO₂ photocatalyst surface between SCA ethanol and LCA n-octanol. To further uncover the mechanism for different selectivities of SCAs and LCAs in photodehydrogenation, in situ electron paramagnetic resonance (EPR) experiments (at 8 K temperature) were employed to observe the oxidation features of photogenerated hole in the valance band of Pt-TiO₂ (h_vb ⁺). The EPR experimental studies exhibited that unlike ethanol, either n-octanol or solvent acetonitrile alone all could not scavenge photogenerated h_vb ⁺ on Pt-P25 photocatalyst and only n-octanol dissolved in acetonitrile solvent could smoothly react with photoinduced hole. This indicated that selective oxidations of LCAs were achieved by solvent-delivered oxidation rather than directly destructive oxidation of photogenerated h_vb ⁺. Our results may open an alternative way in selective dehydrogenative oxidation of various substrates sensitive to both dioxygen and high-temperature treatments.