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A novel visible-light-promoted copper-catalysed process for the Csp–Csp cross-coupling reaction of terminal alkynes at room temperature is described. The current photochemical method is simple, highly functional group compatible, and more viable towards the construction of bio-active 1,3-unsymmetrical conjugated diynes without the need of bases/ligands, additives and expensive palladium/gold catalysts.

A novel domino palladium-catalyzed nitration of Meyer–Schuster intermediates which were generated in situ from propargylic alcohols was developed, by the use of t-BuONO, leading to α-nitro enones in good to excellent yields at room temperature with a broad functional group tolerance.

ConspectusDifunctionalization of alkenes to incorporate two functional groups across a double bond has emerged as a powerful transformation to greatly increase molecular complexity in organic synthesis with improved efficiency. Historically, palladium-catalyzed difunctionalization of alkenes has suffered from difficulties with introducing a second functional group through reductive elimination of a Pd(II) intermediate and competing β-hydride elimination reactions. To overcome these challenges, one strategy involves utilizing a steric bulky ligand to promote the reductive elimination steps from the Pd(II) center and impeding the β-hydride elimination reactions, which are beyond the scope of this Account. Alternatively, strong oxidants have been utilized to generate high-valent palladium species, which are prone to undergo reductive elimination to form a second C–X bond. This new strategy has been extensively applied to explore the difunctionalization of alkenes with enriched functional group diversity over...

Described herein is the GaCl3-catalyzed lactonization of γ-keto carboxylic acids in the presence of PhSiH3 leading to the direct preparation of γ-lactone derivatives. This reducing system showed a relatively wide functional group tolerance.

In this Focus Review, recently reported cascade reactions that are initiated from hydrazones are described. These cascades are grouped based on the mechanistic characteristics of the reactions paired with the hydrazone-based transformations. Reactions in which the hydrazone simply acts as a surrogate for a diazo group are not discussed, but rather the focus is maintained on reactions with multiple mechanistically distinct steps. Sigmatropic, ene–yne metathesis, C−H bond insertion, ylide, and cross-coupling examples are given. The versatility of the hydrazone functional group allows for many transformations, and yet is also compatible with many other transformations. Finally, a discussion of potential future directions for hydrazone-initiated cascades is presented.

A simple and efficient procedure for the one-pot hydrodebromination-hydrogenation of substituted 1-bromo-1-alkenes to give the related ethanes by the pair NiCl2⋅6H2O and NaBH4 (nickel boride) in THF-methanol at room temperature is reported. This unexplored functional group conversion allows completing advantageously the process leading aldehydes into different types 1,2-disubstituted ethanes.

A novel protocol for CuO-catalyzed decarboxylation/elimination of N-arylsulfonyl amino acids was developed. It is the first example of using an accessible amino acid as an ammonia synthetic equivalent for the synthesis of primary aryl sulfonamides via oxidative decarboxylation/elimination reactions. The present protocol shows excellent functional group tolerance and provides an efficient method for the synthesis of primary aryl sulfonamides in excellent yields.

A palladium-catalyzed dearomative allylic alkylation of indoles with alkynes to construct indolenines with C3-quarternary centers was reported. The in situ formed arylallene intermediate omitted the need to install leaving groups on the allylic compounds and employ extra oxidants to oxidize the allylic C–H bonds. The reaction exhibited good functional group tolerance and high atom economy. Moreover, the reaction was further expanded to synthesize pyrroloindolines and furanoindolines.

An efficient catalytic method for α-trifluoromethylthiolation of aldehydes has been developed. The reaction occurred by using an easily accessible reagent and commercially available starting materials. The convenient manipulation and broad functional group tolerance allow the potential of this new methodology to be widely applied in organic synthesis as well as in the industrial, pharmaceutical and agrochemical fields.

A facile and efficient protocol for palladium-catalyzed C8-selective acylation of quinoline N-oxides with α-oxocarboxylic acids has been developed. In this approach, N-oxide was utilized as a stepping stone for the remote C–H functionalization. The reactions proceeded efficiently under mild reaction conditions with excellent regioselectivity and broad functional group tolerance.

The hypervalent-iodine-mediated oxidative metal-free cross-coupling reaction of thiophenes with various pyrroles was developed. The corresponding thiophene–pyrrole derivatives were obtained in moderate to high yields (up to 85 %). This method features high efficiency and regioselectivity and broad functional group tolerance. We further determined the highly planar characteristics of the 3,4-ethylenedioxythiophene–pyrrole biaryls caused by intramolecular hydrogen bonding.

A rhodium(III)-catalyzed C–H/N–H bond functionalization for the synthesis of 1-aminoisoquinolines from aryl amidines and α-MsO/TsO/Cl ketones was achieved under mild reaction conditions. Thus, this approach provides a practical method for the site-selective synthesis of various synthetically valuable isoquinolines with wide functional group tolerance.

Versatile ruthenium(II) complexes derived from amino acids enabled the first general C–H arylations of aryltetrazoles with inexpensive aryl chlorides. The user-friendly Piv-Val-OH-based ruthenium(II) catalyst was characterized by a broad substrate scope, excellent functional group tolerance, and high catalytic activity. Thereby, the ruthenium(II) catalysis set the stage for the step-economical preparation of the blockbuster antihypertension drug Valsartan, while displaying unique robustness in the C–H arylation regime.

A visible-light-induced C-3 selective trifluoroethylation of imidazoheterocycles using 1,1,1-trifluoro-2-iodoethane as trifluoroethyl radical sources was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with excellent regioselectivities and high functional group tolerance.

ConspectusRadical chemistry has witnessed over the last decades important advances that have positioned it as a methodology of choice in synthetic chemistry. A number of great attributes such as specific reactivities, the knowledge of the kinetics of most elementary processes, the functional group tolerance, and the possibility to operate cascade sequences are clearly responsible for this craze. Nevertheless, at the end of the last century, radical chemistry appeared plagued by several hurdles to overcome such as the use of environmentally problematic mediators or the impossibility of scale up. While the concept of photocatalysis was firmly established in the coordination chemistry community, its diffusion in organic synthetic chemistry remained sporadic for decades until the end of the 2000s with the breakthrough merging of organocatalysis and photocatalysis by the MacMillan group and contemporary reports by the groups of Yoon and Stephenson. Since then, photoredox catalysis has enjoyed particularly acti...

A novel [3 + 2] annulation between para-quinone methides and vinylcyclopropanes for the synthesis of spiro[4.5]deca-6,9-diene-8-ones has been described. The palladium and phosphine–thiourea cooperative catalysis system played an important role in high yields and diastereoselectivities. The reaction exhibited good functional group tolerance and scalability.

The recent years have witnessed the development of metal-catalyzed reductive carboxylation of organic (pseudo)halides with CO2 as C1 source, representing potential powerful alternatives to existing methodologies for preparing carboxylic acids, privileged motifs in a myriad of pharmaceuticals and molecules displaying significant biological properties. While originally visualized as exotic cross-coupling reactions, a close look into the literature data indicates that these processes have become a fertile ground, allowing for the utilization of a variety of coupling partners, even with particularly challenging substrate combinations. As for other related cross-electrophile scenarios, the vast majority of reductive carboxylation of organic (pseudo)halides are characterized by their simplicity, mild conditions, and a broad functional group compatibility, suggesting that these processes could be implemented in late-stage diversification. This perspective describes the evolution of metal-catalyzed reductive carb...

A strategy for synthesis of γ-alkylated enones through oxidative coupling of siloxydienes and 1,3-dicarbonyl compounds is reported. This method is an interrupted form of our formal [3 + 2] cycloaddition method reported previously. The present work excels in generating all-carbon quaternary centers via C–C bond formation at the remote γ-site which is traditionally challenging to functionalize. Stereoselectivity and functional group tolerance are examined in complex systems. Double alkylation reactions are also described.

A two-step synthetic strategy toward difluoromethyl ethers via a CuI-catalyzed reaction of the alcohols, bearing additional protected functionalities, with FSO2CF2CO2H has been developed. The high potential of the developed protocol has been shown by preparing novel OCF2H-analogues of GABA and l-proline. The described transformation has good functional group compatibility and can serve as a powerful synthetic tool for late-stage preparation of complex OCF2H-containing organic compounds as well as building blocks for drug discovery.

A photoinduced radical cyclization of benzene-tethered 1,7-enynes with Togni reagent in the presence of sodium iodide is developed. Under ultraviolet irradiation, (Z)-4-(iodomethylene)-3-(2,2,2-trifluoroethyl)-3,4-dihydroquinolin-2(1H)-ones are generated in moderate to good yields. The transformation works well without any metals or photo-redox catalysts at room temperature. During the reaction process, the reaction proceeds through a trifluoromethyl radical-triggered α,β-conjugated addition/intramolecular 6-exo cyclization/iodination, with the formation of multiple bonds. Good functional group tolerance is observed under the reaction conditions.

An efficient transition-metal-free photochemical method featuring excellent functional group tolerance, mild reaction conditions and short reaction times has been discovered and developed for the synthesis of (hetero)aryl trimethylstannanes from (hetero)aryl halides. A photo-initiated radical chain mechanism was proposed based on preliminary mechanistic studies.

The base-free palladium-catalyzed borylation of aryl chlorides with diborons was achieved. The base-free conditions offered acceptable functional group compatibility. Based on experimental and computational studies, it was shown that smooth boryl transfer from the diborons to the arylpalladium chloride was promoted by strong interaction between the Lewis acidic boron and the chlorine atom on palladium.

Various polysubstituted pyrimidines are smoothly formed via a base-promoted intermolecular oxidation C–N bond formation of allylic C(sp3)–H and vinylic C(sp2)–H of allyllic compounds with amidines using O2 as the sole oxidant. This protocol features protecting group free nitrogen sources, good functional group tolerance, high atom economy, and environmental advantages.

A convenient and efficient DABCO-catalyzed formal [4 + 2] cycloaddition of 3-acyl(or alkoxycarbonyl)-1,4-enediones with 2,3-butadienoates is presented. This transformation takes advantage of mild conditions, wide substrate scope and significant functional group tolerance as well as excellent regioselectivity, which makes this method powerful for one-pot synthesis of highly functionalized pyrans in moderate to excellent yields.

A one-pot cascade reaction for the synthesis of 2-BMIDA 6,5-bicyclic heterocycles has been developed using Cu(I)/Pd(0)/Cu(II) catalysis. 2-Iodoanilines and phenols undergo a Cu(I)/Pd(0)-catalyzed Sonogashira reaction with ethynyl BMIDA followed by in situ Cu(II)-catalyzed 5-endo-dig cyclization to generate heterocyclic scaffolds with a BMIDA functional group in the 2-position. The method provides efficient access to borylated indoles, benzofurans, and aza-derivatives, which can be difficult to access through alternative methods.

Copper-promoted direct carbonylation of unactivated sp3 C–H and aromatic sp2 C–H bonds of amides was developed using nitromethane as a novel carbonyl source. The sp3 C–H functionalization showed high site-selectivity by favoring the C–H bonds of α-methyl groups. The sp2 C–H carbonylation featured high regioselectivity and good functional group compatibility. Kinetic isotope effect studies indicated that the sp3 C–H bond breaking step is reversible, whereas the sp2 C–H bond cleavage is an irreversible but not the rate-determining step. Control experiments showed that a nitromethyl intermediate should be involved in the present reaction.

C–H arylations were accomplished with a user-friendly heterogeneous palladium catalyst in the biomass-derived γ-valerolactone (GVL) as an environmentally-benign reaction medium. The user-friendly protocol was characterized by ample substrate scope and high functional group tolerance in the C–H arylation of 1,2,3-triazoles, and the palladium catalyst could be recycled and reused in the C–H activation process.

Carbamoyl fluorides are formed in reactions of hydroxylamines with difluorocarbene generated from sodium bromodifluoroacetate as readily available and non-toxic carbene precursor. The process shows a high functional group tolerance, and the reaction path has been rationalized by computational calculations.

A chemoselective functional group installation through catalytic hydroxy group selective conjugate addition of amino alcohols to a variety of functionalized α,β-unsaturated sulfonyl derivatives was developed. Azide group installation for click chemistry and facile fluorescent labeling onto the less reactive hydroxy group demonstrated the synthetic utility of the present chemoselective catalysis. Moreover, chemo- and regioselective reaction of an unprotected amino diol was achieved for the first time.

ConspectusAromatic fluorides are prevalent in both agrochemical and pharmaceutical agents. However, methods for their rapid and general preparation from widely available starting materials are limited. Traditional approaches such as the Balz–Schiemann and Halex reactions require harsh conditions that limit functional group tolerance and substrate scope. The use of transition metals to affect C–F bond formation has provided some useful alternatives, but a broadly applicable method remains elusive. In contrast to the widespread use of Pd0/PdII catalysis for aryl–Z bond formation (Z = C, N, O), the analogous C–F cross-coupling process was unknown until fairly recently. In large part, this is due to the challenging Ar–F reductive elimination from Pd(II) intermediates. We have discovered that certain biaryl monophosphine ligands are uniquely capable of promoting this transformation. In this Account, we describe the discovery and development of a Pd-catalyzed C–F cross-coupling process and the systematic develo...

A direct C–H thiocyanation of imidazo[1,2-a]pyridines, and a practical sequential one-pot condensation/C–H thiocyanation process, using a combination of N-chlorosuccinimide/NaSCN for the synthesis of 3-thiocyanatoimidazo[1,2-a]pyridines have been developed. The reactions are environmentally friendly, and easy to carry out. They use readily available starting materials and mild reaction conditions, show a wide functional group tolerance, and give good to excellent yields.

ConspectusStereoselective indium-mediated organic reactions have enjoyed tremendous growth in the last 25 years. This is in part due to the insensitivity of allylindium to moisture, affording facile and practical reaction conditions coupled with outstanding functional group tolerance and minimal side reactions. Despite the plethora of articles about allylindium, there is much yet to be discovered and exploited for efficient and sustainable synthesis.In this Account, we describe indium-mediated synthetic methods for the preparation of chiral amines with the aim to present a balance of practical method development, novel asymmetric chemistry, and mechanistic understanding that impact multiple chemical and materials science disciplines. In 2005, we demonstrated the indium-mediated allylation of chiral hydrazones with complete diastereoselectivity (>99:1) and quantitative yields. Further, we revealed the first example of enantioselective indium-mediated allylation of hydrazones using catalytic (R)-3,3′-bis(tr...

A photo-induced substitutive introduction of an aldoxime functional group to carbon chains was achieved using photo-excited 4-benzoylpyridine as a C(sp(3) )-H bond cleaving agent and arylsulfonyl oxime as an aldoxime precursor. The non-acidic C-H bonds in various substances, including cycloalkanes, ethers, azacycles, and cyclic sulfides, were chemoselectively converted at ambient temperature under neutral conditions. The present transformation is a formal formylation of non-acidic C(sp(3) )-H bonds in a single step.

A facile and simple ligand-free copper-catalyzed reaction to synthesize substituted phenols is reported. The reaction presumably proceeds via an O-arylsulfonate intermediate that is hydrolyzed to afford good to excellent yields of up to 88%. This protocol provides an alternative to existing reports which use strong hydroxide salts as the direct hydroxylation partner. Demonstrating a wide substrate scope and functional group tolerance, this protocol can also be applied to inexpensive and commercially available carboxylic acids to yield phenols.

A [Cp*Rh(III)]-catalyzed electrophilic amination of arylboronic acids with diethyl azodicarboxylate (DEAD) was developed, and arylhydrazides were produced in excellent yields and selectivity. The analogous amination with the arylazocarboxylates afforded the corresponding N,N-diarylhydrazides. The electrophilic amination of arylboronic acids with azocarboxylates proceeds readily under mild conditions with excellent functional group tolerance. Up to 99% yields were obtained. Preliminary mechanistic studies revealed that prior formation of an arylrhodium(III) intermediate for the azo coupling reaction can be ruled out.

A copper-catalyzed C–N bond forming reaction of arylboronic acids and N -acylpyrazoles was developed. This procedure used N -acetyl protected pyrazoles as starting material instead of free pyrazoles (NH). The reaction worked under neutral conditions and did not require any base or ligand. The reaction showed good functional group tolerance.

A method for the synthesis of a large number of 1,2-benzothiazines bearing pyridyl as well as carbonyl groups is developed from rhodium-catalyzed carbene insertions into aromatic C–H bonds of S-aryl sulfoximines using pyridotriazoles by denitrogenative cyclization followed by the elimination of alcohols. The present method involves the N–H/C–H activation of simple alkyl aryl sulfoximines and has the advantages of a broad substrate scope, high functional group tolerance, and good regioselectivity.

Herein, we report a simple and metal-free method for the synthesis of N-azine sulfoximines by the nucleophilic substitution of azine N-oxides with NH-sulfoximines. The present method works at room temperature with wide functional group compatibility and gives several unprecedented N-azine sulfoximines. The reaction conditions were also found suitable with enantiopure substrates and furnished products without any racemization. It also finds an application in the sulfoximination of azine-based functional molecules such as 2,2′-bipyridine, 1,10-phenanthroline, and quinine.

A transformation analogous in simplicity and functional group tolerance to the venerable Suzuki cross-coupling between alkyl-carboxylic acids and boronic acids is described. This Ni-catalyzed reaction relies upon the activation of alkyl carboxylic acids as their redox-active ester derivatives, specifically N-hydroxy-tetrachlorophthalimide (TCNHPI), and proceeds in a practical and scalable fashion. The inexpensive nature of the reaction components (NiCl2 ⋅6 H2 O-$9.5 mol(-1) , Et3 N) coupled to the virtually unlimited commercial catalog of available starting materials bodes well for its rapid adoption.

A general regio- and stereoselective γ-C–C bond formation is achieved using α-halocarbonyl compounds and dienol ethers via Cu(II) catalysis. This method constitutes a novel approach to the challenging 1,6-dioxygenation motif. A range of γ-substituted enones, including many bearing all-carbon quaternary centers, are available through a simple protocol under mild reaction conditions with superb functional group compatibility. Excellent stereoinduction is observed providing controlled access to challenging stereochemical arrays.

A 1,6-addition arylation reaction of para-quinone methides with α-isocyanoacetamides and electron-rich aromatic compounds under metal-free conditions has been developed. BF3·Et2O plays two roles in the reaction: catalyzing the cyclization of α-isocyanoacetamides to give oxazoles, and activating the para-quinone methides to achieve the 1,6-addition arylation process. The reaction shows good functional group tolerance, scalability, and regioselectivity. It is a consice protocol for the synthesis of diverse unsymmetrical triarylmethanes. Further transformation of the resulting triarylmethanes provides an efficient route to some functionalized molecules.

A novel and efficient Cu(I)-catalyzed ligand- and base-free multipathway domino strategy has been developed for the synthesis of 2-substituted quinazolinones. The reaction utilizes 2-bromobenzamide and multiform substrates such as aldehydes, alcohols, and methyl arenes for a one-pot protocol, whereas TMSN3 is used as a nitrogen source. A wide range of substrate scope, functional group tolerance, and operational simplicity are synthetically useful features.

Recent developments in the photochemical carbon–carbon and carbon–heteroatom bond formation via photoinduced Ar–X bond dissociation are summarized. The transformations through the Ar–X bond dissociation enabled by photoenergy include nucleophilic substitution, arylation, alkylation, aminocarbonylation, aminosulfonylation and decarboxylative coupling reactions. Usually, the reactions undergo one-electron-transfer couplings and aryl radicals or cations are involved as the key intermediates. Under ultraviolet irradiation or visible light, the reactions of aryl halides with reactive partners proceed smoothly under mild conditions. In some cases, the transformations can proceed without any metals or photo-redox catalysts. Moreover, the broad reaction scope is demonstrated with good functional group tolerance.

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.

A new metal-free catalysis protocol for the oxidative coupling of nonactivated alkenes with simple carboxylic acids has been established. This method is predicated on the cooperative interaction of a diselane and a photoredox catalyst, which allows for the use of ambient air or pure O2 as the terminal oxidant. Under the title conditions, a range of both functionalized and nonfunctionalized alkenes can be readily converted into the corresponding allylic ester products with good yields (up to 89%) and excellent regioselectivity as well as good functional group tolerance.

A new method for the synthesis of secondary thiocarbamates from readily available isocyanides and thiosulfonates with broad functional group tolerance is reported. The reaction proceeds under mild reaction conditions in isopropanol and is catalyzed by inexpensive sodium iodide.

Recent advances in photoinduced trifluoromethylation and difluoroalkylation under photocatalysis are summarized. Most of the photoredox reactions proceed efficiently under mild conditions with simple operation. Various fluorinated reagents are developed and applied in different transformations. Usually, the photocatalyst in a photocatalytic cycle is initially stimulated to the excited state in the presence of visible light, which then provides an electron to the fluorinated reagent to release a CF3 radical or CF2 radical. The subsequent radical addition to an unsaturated bond with further transformations would produce the corresponding fluorinated products. Alkenes, alkynes, isocyanides, and arenes are frequently employed as substrates for access to fluorochemicals. The advantages of trifluoromethylation and difluoroalkylation under photocatalysis including mild reaction conditions, good functional group tolerance, and experimental ease will make the approaches attractive for further applications.

Because of the unique properties of the trifluoromethoxy group, molecules bearing this moiety will find applications in various fields, particularly in the life sciences. However, despite the great interest in this functional group, only a small number of trifluoromethoxylated molecules are currently synthetically accessible. Over the last few years, several innovative and promising strategies for the synthesis of trifluoromethoxylated compounds have been described. This Minireview discusses these existing methods with a particular focus on more recent advances.

Base mediated deacylation of α-diazo-β-ketoester generates diazoester anion, a reactive 1,3-dipole, which undergoes [3+2] annulation with chalcones to afford pyrazole ketoesters. Under similar conditions, the 1,3-dipole takes part in a [3+3] annulation with chalcone epoxides to provide pyridazine esters. Despite moderate yields, high regioselectivity, mild conditions, and functional group diversity are the salient features of this novel methodology.

A BF3-etherate-promoted cascade reaction of nitriles with 2-alkynylanilines is described. This method achieves the formation of two new C–N bonds through a reaction sequence of diazotization with t-BuONO, nucleophilic addition of the alkyne to the BF3-coordinated diazonium ion, followed by nitrile addition to the intermediary vinyl cation and hydrolysis. The method provides efficient and general access to a variety of 4-amido-cinnolines. Notable features of the method include its broad functional group tolerance and avoidance of transition metals.