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Selective functionalisation of synthetically useful vinyl epoxides via carbon-carbon (C-C) bond formation has been a major challenge for many years due to its unique inherent chemical reactivity. Non-stabilised carbanions in the form of organometallic reagents have been shown to be robust and versatile reagents in C-C bond formation; however, they are employed in superstoichiometric quantities, require the protection of active functional groups, and generate copious amounts of metallic waste. Therefore, the development of mild carbanion sources as simple alternatives is highly desired. In this work, we report a highly chemo- and regioselective palladium-catalysed vinyl epoxide cross-coupling utilising hydrazones as organometallic equivalents (HOME). Hydrazones, generated from carbonyl-containing renewable feedstocks, enable a more sustainable reaction, and provide an alternative to highly reactive and sensitive unstabilized organometallic reagents. A broad substrate scope, with high functional group tolerance, is demonstrated along with the late-stage functionalisation of natural product derivatives., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Transition-metal-catalyzed double/triple bond metathesis reactions have been well-established due to the ability of transition-metal catalysts to readily interact with π bonds, facilitating the progression of the entire reaction. However, activating σ-bonds to induce σ-bond metathesis is more challenging due to the absence of π bonds and the high bond energy of σ bonds. In this study, we present a novel photo-induced approach that does not rely on transition metals or photosensitizers to drive C-C and C-N σ-bond metathesis reactions. This method enables the cross-coupling of tertiary amines with α-diketones via C-C and C-N single bonds cleavage and recombination. Notably, our protocol exhibits good compatibility with various functional groups in the absence of transition metals and external photosensitizers, resulting in the formation of aryl alkyl ketones and aromatic amides in good to high yields. To gain insights into the mechanism of this pathway, we conducted controlled experiments, intermediate trapping experiments, and DFT (Density Functional Theory) calculations. This comprehensive approach allowed us to elucidate the detailed mechanism underlying this transformative reaction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In the vast majority of top-selling pharmaceutical and industrial products, phenolic structural motifs are highly prevalent. Non-functionalized simple phenols serve as building blocks in the synthesis of value-added chemicals. It is worth mentioning that lignin, being the largest renewable biomass source of aromatic building blocks in nature, mainly consists of phenolic units, which enable the production of structurally diverse phenols. Given their remarkable applicability in the chemical value chain, many efforts have been devoted to increasing the molecular complexity of the phenolic scaffold. Among the key techniques, direct functionalization of Csp 2 -H is a powerful tool, enabling the construction of new Csp 2 -C bonds in an economical and atomic manner. Herein we present and summarize the large plethora of direct Csp 2 -H functionalization methods that enables scaffold diversification of simple, unprotected phenols, leading to the formation of new Csp 2 -C bonds. In this review article, we intend to summarize the contributions that appeared in the literature mainly in the last 5 years dealing with the functionalization of unprotected phenols, both catalytic and non-catalytic. Our goal is to highlight the key findings and the ongoing challenges in the stimulating and growing research dedicated to the development of new protocols for the valorization of phenols., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

One of the most widely utilized methods for the construction of C(sp 2 )-N bonds is the transition-metal-catalyzed cross-coupling of aryl halides/boronic acids with amines, known as Ullmann condensation, Buchwald-Hartwig amination, and Chan-Lam coupling. However, aryl halides/boronic acids often require multi-step preparation while generating a large amount of corrosive and toxic waste, making the reaction less attractive. Herein, we present an unprecedented method for the C(sp 2 )-N formation via Buchwald-Hartwig-type reactions using synthetically upstream nitroarenes as the sole starting materials, thus eliminating the need for arylhalides and pre-formed arylamines. A diverse range of symmetrical di- and triarylamines were obtained in a single step from nitroarenes, and more importantly, various unsymmetrical di- and triarylamines were also highly selectively synthesized in a one-pot/two-step process. Furthermore, the success of the scale-up experiments, the late-stage functionalization of a drug intermediate, and the rapid preparation of hole-transporting material TCTA showcased the utility and practicality of this protocol in synthetic chemistry. Mechanistic studies indicate that this transformation may proceed via an arylamine intermediate generated in situ from the reduction of nitroarenes, which is followed by a denitrative Buchwald-Hartwig-type reaction with another nitroarene to form a C-N bond., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The direct functionalization of inert C-H bonds has long been a "holy grail" for the chemistry world. In this report, the direct C(sp 3 )-N bond formation of unactivated alkanes is reported with a GaN based Mott-Schottky catalyst under photocatalytic reaction conditions. Long term stability and reaction efficiency (up to 92%) were achieved with this photocatalyst. The deposition of a Pd co-catalyst on the surface of GaN significantly enhanced the reaction efficiency. Microscopic investigation suggested a remarkable interaction in the Pd/GaN Schottky junction, giving a significant Pd/GaN depletion layer. In addition, density functional theory (DFT) calculations were performed to show the distinct performance of Pd nanoparticles at the atomic level., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Recently, photochemistry of Electron Donor-Acceptor (EDA) complexes employing catalytic amounts of electron donors have become of interest as a new methodology in the catalysis field, allowing for decoupling of the electron transfer (ET) from the bond-forming event. However, examples of practical EDA systems in the catalytic regime remain scarce, and their mechanism is not yet well-understood. Herein, we report the discovery of an EDA complex between triarylamines and α-perfluorosulfonylpropiophenone reagents, catalyzing C-H perfluoroalkylation of arenes and heteroarenes under visible light irradiation in pH- and redox-neutral conditions. We elucidate the mechanism of this reaction using a detailed photophysical characterization of the EDA complex, the resulting triarylamine radical cation, and its turnover event., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Despite their long-known photochemical properties and their industrial value, the use of nitroarenes as a productive photochemical handle in organic synthesis has remained relatively unexplored. More specifically, the photochemical formation of nitrogen-sulfur bonds from nitroarenes remains to be demonstrated. Herein, we report the design and application of a sulfinate-nitroarene electron donor-acceptor (EDA) complex and its subsequent use in the first light mediated catalyst-free synthesis of N- hydroxy-sulfonamides. The presence of the EDA was assessed spectroscopically and studied via DFT and TD-DFT calculations. A total of 32 examples including both electron withdrawing and electron donating groups were synthesized under our oxygen- and water-tolerant conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

C(sp 3 ) radicals (R˙) are of broad research interest and synthetic utility. This review collects some of the most recent advancements in photocatalytic R˙ generation and highlights representative examples in this field. Based on the key bond cleavages that generate R˙, these contributions are divided into C-H, C-C, and C-X bond cleavages. A general mechanistic scenario and key R˙-forming steps are presented and discussed in each section., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The decarbonylative-coupling reaction is generally promoted by transition metals ( via organometallic complexes) or peroxides ( via radical intermediates), often at high temperatures to facilitate the CO release. Herein, a visible-light-induced, transition metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes at room temperature is reported. Tertiary/secondary alcohols were obtained in moderate to excellent yields promoted by using CsF under mild conditions. The detailed mechanistic investigation showed that the reaction proceeded through photoexcitation-decarbonylation of the aldehyde to generate an aromatic anion, followed by its addition to ketones/aldehydes. The reaction mechanism was verified by the density functional theory (DFT) calculations., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

One of the most efficient and reliable approaches to construct C-C bonds involves the conjugate addition of carbon nucleophiles to electron-deficient ketones. Yet, 1,6-conjugate additions of extended conjugated systems largely remain underexplored due to difficulties in controlling the regioselectivity. Herein, we report umpolung aldehydes as carbanion equivalents for highly regioselective 1,6-conjugate addition reactions to unsaturated ketones, with preliminary studies of the enantioselective variant. The synergy of ruthenium(ii) catalyst and electron-rich, bidentate phosphine ligand is essential for the reactivity and selectivity under mild reaction conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Umpolung (polarity reversal) tactics of aldehydes/ketones have greatly broadened carbonyl chemistry by enabling transformations with electrophilic reagents and deoxygenative functionalizations. Herein, we report the first ruthenium-catalyzed β-selective alkylation of vinylpyridines with both naturally abundant aromatic and aliphatic aldehyde/ketones via N 2 H 4 mediated deoxygenative couplings. Compared with one-electron umpolung of carbonyls to alcohols, this two-electron umpolung strategy realized reductive deoxygenation targets, which were not only applicable to the regioselective alkylation of a broad range of 2/4-alkene substituted pyridines, but also amenable to challenging 3-vinyl and steric-embedded internal pyridines as well as their analogous heterocyclic structures., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Employing photo-energy to drive the desired chemical transformation has been a long pursued subject. The development of homogeneous photoredox catalysts in radical coupling reactions has been truly phenomenal, however, with apparent disadvantages such as the difficulty in separating the catalyst and the frequent requirement of scarce noble metals. We therefore envisioned the use of a hyper-stable III-V photosensitizing semiconductor with a tunable Fermi level and energy band as a readily isolable and recyclable heterogeneous photoredox catalyst for radical coupling reactions. Using the carbonyl coupling reaction as a proof-of-concept, herein, we report a photo-pinacol coupling reaction catalyzed by GaN nanowires under ambient light at room temperature with methanol as a solvent and sacrificial reagent. By simply tuning the dopant, the GaN nanowire shows significantly enhanced electronic properties. The catalyst showed excellent stability, reusability and functional tolerance. All reactions could be accomplished with a single piece of nanowire on Si-wafer., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The use of photochemical reactions that do not require expensive photocatalysts or transition metals is an environmentally friendly strategy for accomplishing a variety of structural transformations. Herein, we report a protocol for photoinduced transition-metal- and external-photocatalyst-free intramolecular heteroaryl/aryl rearrangement reactions of 2-heteroaryl/aryloxybenzaldehydes. The protocol was compatible with a variety of functionalities, including methyl, methoxy, cyano, ester, trifluoromethyl, halogen, and heteroaromatic rings. Control experiments suggested that the reaction proceeded via a photoinduced intramolecular heteroaryl/aryl rearrangement process involving photoexcitation of the aldehyde carbonyl group, radical addition, C-C bond formation and C(Ar)-O bond cleavage., (This journal is © The Royal Society of Chemistry 2020.)

A palladium-catalyzed hydroalkylation reaction of methylenecyclopropanes via highly selective C-C σ-bond scission was achieved under mild conditions, in which simple hydrazones served as carbanion equivalents. This method featured good functional group compatibility, affording high yields of C-alkylated terminal alkenes., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Efficient carbon-carbon bond formation is of great importance in modern organic synthetic chemistry. The pinacol coupling discovered over a century ago is still one of the most efficient coupling reactions to build the C-C bond in one step. However, traditional pinacol coupling often requires over-stoichiometric amounts of active metals as reductants, causing long-lasting metal waste issues and sustainability concerns. A great scientific challenge is to design a metal-free approach to the pinacol coupling reaction. Herein, we describe a light-driven pinacol coupling protocol without use of any metals, but with N 2 H 4 , used as a clean non-metallic hydrogen-atom-transfer (HAT) reductant. In this transformation, only traceless non-toxic N 2 and H 2 gases were produced as by-products with a relatively broad aromatic ketone scope and good functional group tolerance. A combined experimental and computational investigation of the mechanism suggests that this novel pinacol coupling reaction proceeds via a HAT process between photo-excited ketone and N 2 H 4 , instead of the common single-electron-transfer (SET) process for metal reductants., (This journal is © The Royal Society of Chemistry 2019.)

Minisci alkylation is of prime importance for its applicability in functionalizing diverse heteroarenes, which are core structures in many bioactive compounds. In alkyl radical generation processes, precious metal catalysts, high temperatures and excessive oxidants are generally involved, which lead to sustainability and safety concerns. Herein we report a new strategy using diacetyl (2,3-butanedione) as an abundant, visible light-sensitive and "traceless" hydrogen atom abstractor to achieve metal-free cross-dehydrogenative Minisci alkylation under mild conditions. Mechanistic studies supported hydrogen atom transfer (HAT) between an activated C(sp 3 )-H substrate and diacetyl. Moreover, with the assistance of di- tert -butyl peroxide (DTBP), the scope of the reaction could be extended to strong aliphatic C-H bonds via diacetyl-mediated energy transfer. The robustness of this strategy was demonstrated by functionalizing complex molecules such as quinine, fasudil, nicotine, menthol and alanine derivatives.

Primary anilines are essential building blocks to synthesize various pharmaceuticals, agrochemicals, pigments, electronic materials, and others. To date, the syntheses of primary anilines mostly rely on the reduction of nitroarenes or the transition-metal-catalyzed Ullmann, Buchwald-Hartwig and Chan-Lam cross-coupling reactions with ammonia, in which non-renewable petroleum-based chemicals are typically used as feedstocks via multiple step syntheses. A long-standing scientific challenge is to synthesize various primary anilines directly from renewable sources. Herein, we report a general method to directly convert a broad range of phenols into the corresponding primary anilines with the cheap and widely available hydrazine as both amine and hydride sources with simple Pd/C as the catalyst.

This perspective report presents the key approaches for the development of various organometallic reactions in aqueous media. In view of future sustainability, the efficient use of natural resources, such as renewable biomass-based feedstocks, constitutes an important aspect for sustainable chemical industry. The exploration and discovery of efficient organometallic reactions or equivalents in water enrich the toolbox of organic chemists for the direct conversion of biomass-derived feedstocks into high-valued chemicals and the direct modification of biomolecules in their native aqueous environment, which contributes to future sustainability.

Direct introduction of a difluoromethylthio group (-SCF 2 H) to arenes represents an efficient route to access a valuable catalogue of organofluorines; however, to realize this transformation under metal-free and mild conditions still remains challenging and rarely reported. Herein, a metal-catalyst-free and redox-neutral innate difluoromethylthiolation method with a shelf-stable and readily available reagent, PhSO 2 SCF 2 H, under visible light irradiation is described. This light-mediated protocol successfully converts a broad spectrum of arenes and heteroarenes to difluoromethylthioethers in the absence of noble metals and stoichiometric amounts of additives.

The first ruthenium-catalyzed umpolung carboxylation of hydrazones with CO 2 to generate important aryl acetic acids is reported. Besides aldehyde hydrazones, a variety of ketone hydrazones, which have not been successfully applied in previous umpolung reactions with other reactive electrophiles, also show high reactivity and selectivity under mild conditions. Moreover, this operationally simple protocol features good functional group tolerance, is readily scalable, and offers easy derivation of important structures, including bioactive felbinac and adiphenine. Computational studies reveal that this umpolung reaction proceeds through the generation of a Ru-nitrenoid followed by concerted [4 + 2] cycloaddition with CO 2 .

Natural availability of carbonyl groups offers reductive carbonyl coupling tremendous synthetic potential for efficient olefin synthesis, yet the catalytic carbonyl cross-coupling remains largely elusive. We report herein such a reaction, mediated by hydrazine under ruthenium(ii) catalysis. This method enables facile and selective cross-couplings of two unsymmetrical carbonyl compounds in either an intermolecular or intramolecular fashion. Moreover, this chemistry accommodates a variety of substrates, proceeds under mild reaction conditions with good functional group tolerance, and generates stoichiometric benign byproducts. Importantly, the coexistence of KO t Bu and bidentate phosphine dmpe is vital to this transformation.

We herein describe a palladium-catalyzed formal aromaticity transfer coupling reaction between phenols and pyrrolidines or indolines to generate the corresponding N -cyclohexyl pyrroles or indoles. In this transformation, the aromaticity of phenols is formally passed on to the pyrrolidine or indoline units. Substituted phenols thus can serve as latent cyclohexyl equivalents for the fast construction of various N -cyclohexyl pyrroles and indoles.

We report the first cationic gold(i)-catalyzed one-pot reaction of amide, alkyne and aldehyde followed by cyclization, to successfully access highly substituted oxazoles derivatives in good yields. A single catalyst allows the occurring of this multi-step reaction atom- and step-economically, with water as the only theoretical side product.

Phenols, being readily available from naturally abundant lignins, are important future feedstocks for the renewable production of fuels, chemicals, and energy. Herein, a highly efficient Pd-catalyzed direct coupling of phenolic lignin model monomers and analogues with anilines to give cyclohexylamines using cheap and safe sodium formate as hydrogen donor is described. A variety of secondary and tertiary substituted cyclohexylamines can be synthesized under convenient conditions in moderate to excellent yields.