Photoredox/Bismuth Relay Catalysis Enabling Reductive Alkylation of Nitroarenes with Aldehydes.

The effective transition metal-free photoredox/bismuth dual catalytic reductive dialkylation of nitroarenes with benzaldehydes has been reported. The nitroarene reduction through visible light-driven photoredox catalysis was integrated with subsequent reductive dialkylation of anilines under bismuth catalysis to enable the cascade reductive alkylation of nitroarenes with carbonyls. Salient features of this relay catalysis system include mild reaction conditions, no requirement for transition metal catalysts, easy handling, step-economy, and high selectivity.

General Defluoroalkylation of Trifluoromethylarenes with Both Electron-Donating and -Withdrawing Alkenes.

The incorporation of gem-difluoromethylene units into organic molecules remains a formidable challenge. Conventional methodologies for constructing aryldifluoromethyl derivatives relied on the use of high-functional fluorinating regents under harsh conditions. Herein, we report general and efficient photoredox catalytic systems for defluoroalkylation of readily available trifluoromethylarenes through selective C-F cleavage to deliver gem-difluoromethyl radicals which proceed through reductive addition to both electron-donating and withdrawing alkenes under transition-metal free conditions. Mechanistic studies reveal that thiol serves as both photocatalyst and HAT reagent under visible light irradiation. This synergistic photocatalysis and HAT catalysis protocol exhibits ample and salient features such as high chemo- and regioselectivity, broad substrate scope, amenable gram-scale synthesis and late-stage modification of bioactive molecules.

Formation of cyclopenta[c]quinolines through visible-light-induced photoredox cascade bis-annulations of 1,7-enynes with sulfoxonium ylides.

A novel visible-light-driven photoredox-catalyzed cascade bicyclization of 1,7-enynes with aqueous sulfoxonium ylides is reported. The reaction is highly chemoselective with three new C-C bonds, two new rings, and an all-carbon quaternary stereocenter constructed in a one-pot fashion. This mild protocol features a remarkably broad substrate scope with good functional group tolerance, providing a general and practical approach to access various cyclopenta[c]quinolines.

TBHP-mediated photochemical coupling/cyclization of N-arylacrylamides with thiols.

The effective photoredox-mediated oxidative thiolation and cyclization of N-arylacrylamides with thiols leads to biologically interesting 3-thionated oxindoles through C-S and C-C bond formation. This process represents a straightforward reaction that starts from non-prefunctionalized thiolating reagents. Mechanistic studies demonstrated that the TBHP serves as a key radical initiator with visible-light catalysis.

Recent Advances in Molecule Synthesis Involving C-C Bond Cleavage of Ketoxime Esters.

The synthetic strategies of oxime derivatives participating in radical-type reactions have been rapidly developed in the last few decades. Among them, the N-O bond cleavage of oxime esters leading to formation of nitrogen-centered radicals triggers adjacent C-C bond cleavage to produce carbon-centered free radicals, which has been virtually used in organic synthesis in recent years. Herein, we summarized the radical reactions involving oxime N-O bond and C-C bond cleavage through this special reaction form, including those from acyl oxime ester derivatives and cyclic ketoxime ester derivatives. These contents were systematically classified according to different reaction types. In this review, the free radical reactions involving acyl oxime esters and cyclic ketoxime esters after 2021 were included, with emphasis on the substrate scope and reaction mechanism.

Site-Selective Synthesis of Aryl Sulfides via Oxidative Aromatization of Cyclohexanones with Thiophenols.

We have introduced a metal-free facile access for the thiolation/aromatization of cyclohexanones with thiophenols to the corresponding aryl sulfides. The dehydroaromatic reaction of non-aromatic cyclohexanones proceeded smoothly using oxygen as a green oxidant.

Photoredox Neutral Decarboxylative Hydroxyalkylations of Heteroarenes with α-Keto Acids.

Photoredox neutral decarboxylative hydroxyalkylations of heteroarenes with α-keto acids under mild conditions are described. Stable and readily available α-keto acids were employed as hydroxyalkylating reagents with only CO2 released as the byproduct. A range of aromatic and aliphatic α-keto acids were successfully converted into hydroxyalkylated products with various heteroarenes. This transformation proceeded through a decarboxylation/Minisci addition/SCS sequence, generating a variety of valuable hydroxyalkylated heteroarenes.

Copper-catalyzed three-component N-alkylation of quinazolinones and azoles.

A Cu-catalyzed three-component N-alkylation coupling reaction of N-heteroarenes with methyl ketones and DMPA as a carbon source has been developed. Using methyl ketones as alkylation reagents and DMPA (N,N'-dimethylpropionamide) as a carbon source, the reaction proceeded smoothly under the Cu-based oxidative system and led to a series of functionalized N-heterocycles including 4-quinazolinones, triazoles and pyrazoles.

Progress in C-C and C-Heteroatom Bonds Construction Using Alcohols as Acyl Precursors.

Acyl moiety is a common structural unit in organic molecules, thus acylation methods have been widely explored to construct various functional compounds. While the traditional Friedel-Crafts acylation processes work to allow viable construction of arylketones under harsh acid conditions, recent progress on developing acylation methods focused on the new reactivity discovery by exploiting versatile and easily accessible acylating reagents. Of them, alcohols are cheap, have low toxicity, and are naturally abundant feedstocks; thus, they were recently used as ideal acyl precursors in molecule synthesis for ketones, esters, amides, etc. In this review, we display and discuss recent advances in employing alcohols as unusual acyl sources to form C-C and C-heteroatom bonds, with emphasis on the substrate scope, limitations, and mechanism.

Metal-Free Synthesis and Photophysical Properties of 1,2,4-Triarylpyrroles.

A three-component reaction has been developed for the construction of multiaryl-substituted pyrrole derivatives from arylketones, amines, and nitrovinylarenes under metal-free conditions. Hence, homologous 1,2,4-triaryl-substituted pyrrole products were obtained in good to high yields. Furthermore, 2,3,5-triaryl-substituted pyrroles were selectively formed in the absence of nitrovinylarenes. The photophysical properties of some pyrrole products have been investigated to show good aggregation-induced emission (AIE) activity.

Recent advances in the transition metal-free oxidative dehydrogenative aromatization of cyclohexanones.

Cyclohexanone is a simple and widely available raw material that can be obtained from lignin biomass, highlighting its renewable and sustainable features. Cyclohexanone, as an important synthon in organic chemistry, has been demonstrated to be viable for constructing functionalized arenes and benzoheteroarenes, with recent extensive development on transition metal-free oxidative dehydrogenative aromatization. This review focuses on recent research progress on the transition metal-free derivation of cyclohexanones via oxidative dehydrogenative aromatization.

Copper-catalyzed three-component formal [3 + 1 + 2] annulations for the synthesis of 2-aminopyrimidines from O-acyl ketoximes.

A copper-based catalytic system has been developed to enable formal [3 + 1 + 2] annulations of ketoxime acetates, aldehydes, and cyanamides. This protocol offers a new strategy for the synthesis of highly substituted 2-aminopyrimidine compounds, and more importantly, pyrimidines have now been included in the N-heterocycle family constructed using O-acyl ketoximes as N-C-C synthons.

NH4I-promoted oxidative formation of benzothiazoles and thiazoles from arylacetic acids and phenylalanines with elemental sulfur.

A NH4I/K3PO4-based catalytic system has been established to enable oxidative formation of thiazole compounds from arylacetic acids and phenylalanines with elemental sulfur. While the three-component reaction of anilines or ß-naphthylamines with arylacetic acids and elemental sulfur affords benzo[2,1-d]thiazoles and naphtho[2,1-d]thiazoles, the annulation of phenylalanines with elemental sulfur produces 2-benzyl and 2-benzoylthiazoles. This work well complements previous three-component annulations of benzothiazoles from other coupling partners.

Visible-light- and bromide-mediated photoredox Minisci alkylation of N-heteroarenes with ester acetates.

A visible-light-induced photoredox Minisci alkylation reaction of N-heteroarenes with ethyl acetate has been reported. The low-toxic ethyl acetate was used for the first time as an alkylation reagent. Hence, 4-quinazolinones, quinolines and pyridines reacted smoothly in the current reaction system. Mechanistic studies indicate that LiBr plays a key role to dramatically improve the efficiency of the reaction by the mediation of hydrogen atom transfer.

Elemental Sulfur-Promoted Aerobic Dehydrogenative Aromatization of Cyclohexanones with Amines.

An elemental sulfur-promoted aerobic dehydrogenation system for the access to N,N'-dialkyl-o-phenylenediamines and N-substituted 2-naphthylamines is reported herein. Readily available cyclohexanones and amines (especially alkylamines) are transformed smoothly to target products. Aromatic amines can be achieved from all aliphatic reagents under aerobic metal-free reaction conditions. Control reactions show that the combinational use of elemental sulfur and molecular oxygen is exceptionally essential for this dehydrogenative aromatizaiton.

Three-component synthesis of 1,4-benzothiazines via iodide-catalyzed aerobic C-H sulfuration with elemental sulfur.

Herein, iodide-catalyzed aerobic synthesis of 1,4-benzothiazines via functionalization of multiple C-H bonds with elemental sulfur is described. Beyond the well-established thiazole formation from elemental sulfur, this method provides the first access to the corresponding six-membered N,S-heterocyclic products via direct functionalization of multiple C-H bonds. Hence, 1,4-benzothiazine products were generated in satisfactory yields with a range of compatible functionalities.

Base-controlled divergent synthesis of vinyl sulfones from (benzylsulfonyl)benzenes and paraformaldehyde.

A tuneable metal-free protocol for the selective preparation of α-substituted vinyl sulfone and (E)-vinyl sulfone derivatives has been described. In this process, stable paraformaldehyde was used as the carbon source. The base played an important role in the selectivity control of transformations. More than 50 products were synthesized with excellent chemoselectivity and broad functional group tolerance.

Unveiling the Advances of Nanostructure Design for Alloy-Type Potassium-Ion Battery Anodes via In†Situ TEM.

Nanostructure design and in situ transmission electron microscopy (TEM) are combined to demonstrate Sb-based nanofibers composed of bunched yolk-shell building units as a significantly improved anode for potassium-ion batteries (PIBs). Particularly, a metal-organic frameworks (MOFs)-engaged electrospinning strategy coupled to a confined ion-exchange followed by a subsequent thermal reduction is proposed to fabricate yolk-shell Sb@C nanoboxes embedded in carbon nanofibers (Sb@CNFs). In situ TEM analysis reveals that the inner Sb nanoparticles undergo a significant volume expansion/contraction during the alloying/dealloying processes, while the void space can effectively relieve the overall volume change, and the plastic carbon shell maintains the structural integrity of electrode material. This work provides an important reference for the application of advanced characterization techniques to guide the optimization of electrode material design.

Ordered Macro-Microporous Metal-Organic Framework Single Crystals and Their Derivatives for Rechargeable Aluminum-Ion Batteries.

Constructing ordered hierarchical porous structures while maintaining their overall crystalline order is highly desirable but remains an arduous challenge. Herein, we successfully achieve the growth of single-crystalline metal-organic frameworks (MOFs) in three-dimensional (3D) ordered macroporous template voids by a saturated solution-based double-solvent-assisted strategy with precise control over the nucleation process. The as-prepared single-crystalline ordered macro-microporous Co-based MOFs (SOM ZIF-67) exhibit an ordered macro-microporous structure with robust single-crystalline nature. Moreover, SOM ZIF-67 can serve as a precursor to derive 3D-ordered macroporous cobalt diselenide@carbon (3DOM CoSe2@C) through a facile carbonization-selenization treatment. The as-derived 3DOM CoSe2@C can well preserve the 3D-ordered macroporous structure of the precursor. More importantly, CoSe2 nanoparticles could be uniformly confined in the conductive ordered macroporous carbon framework, affording regularly interconnected macroporous channels and large surface area. As a result, when evaluated as a cathode material for aluminum-ion batteries, the ordered macroporous structure could not only effectively facilitate the diffusion of large-sized chloroaluminate anions but also increase the contact area with electrolyte and provide more exposed active sites, thereby exhibiting superior reversible rate capacity (86 mA h g-1 at 5.0 A g-1) and remarkable cycling performance (125 mA h g-1 after 1000 cycles at 2.0 A g-1).

Three-Component Cascade Synthesis of Carbazoles through [1s,6s] Sigmatropic Shift under Metal-Free Conditions.

A novel method was developed for the synthesis of substituted carbazoles from commercially available starting materials under metal-free conditions. This strategy involves a [1s,6s] sigmatropic shift step and introduces an electron-withdrawing ester substituent at the C2 position of the carbazole ring. The present protocol afforded the desired carbazole derivatives with good regioselectivity and well functional group tolerance. DFT calculations were carried out to support the reaction pathway.