Advancements in hydrochlorination of alkenes

The hydrochlorination of alkenes has been extensively studied in research and is commonly featured in organic chemistry textbooks as an exemplification of the Markovnikov rule. However, the application of this reaction is typically limited to specific alkenes, such as highly substituted ones, styrenes, or strained systems. Conversely, monosubstituted or 1,2-disubstituted alkenes do not readily react with HCl gas or solutions of HCl gas at practical rates. The challenges associated with hydrochlorination reactions for these "non-activated" alkenes have spurred considerable research efforts over the past 30 years, which constitute the primary focus of this review. The discussion begins with classical polar hydrochlorinations, followed by metal-promoted radical hydrochlorinations, and concludes with a brief overview of recent anti-Markovnikov hydrochlorinations.

Ligand Relay Catalysis Enables Asymmetric Migratory Hydroarylation for the Concise Synthesis of Chiral α-(Hetero)Aryl-Substituted Amines

Complementary to the design of a single structurally complex chiral ligand to promote each step in transition-metal catalysis, multiligand relay catalysis through dynamic ligand exchange with each step in the catalytic cycle promoted by its best ligand provides an attractive approach to enhance the whole reaction reactivity and selectivity. Herein, a regio- and enantioselective NiH-catalyzed migratory hydroarylation process with a simple combination of a chain-walking ligand and an asymmetric arylation ligand, producing high-value chiral α-(hetero)aryl-substituted amines and their derivatives under mild conditions, is reported. The potential synthetic applications of this transformation are demonstrated by the concise synthesis of (S)-nicotine and a CDK8 inhibitor.

Stereoselective Synthesis of Complex Polyenes through Sequential α-/β-C-H Functionalization of trans-Styrenes

Sequential C-H functionalization of molecules containing multiple C-H bonds can efficiently lead to structural diversity. Herein we present the first chelation-assisted sequential α-/β-C-H functionalization of E-styrenes with simple alkenes and alkynes in excellent regio- and stereo-selectivity. The process involves α C-H functionalization by six-membered exo-cyclopalladation to result in tri- and tetrasubstituted 1,3-dienes and β C-H functionalization through seven-membered endo-cyclopalladation to produce tetra- and pentasubstituted 1,3,5-trienes in up to 97 % yield with up to >99/1 E/Z selectivity, both enabled by the chelation assistance of pyrazinamide. The protocol is demonstrated to be widely applicable, tolerant to a wide range of functional groups and bioactive fragments, and suitable for gram-scale synthesis as well as one-pot and two step preparation of trienes. Mechanistic experiments and density functional theory (DFT) calculations were performed to elucidate the selectivity and reactivity.

Metal-Free Selective Synthesis of α,β-Unsaturated Aldehydes from Alkenes and Formaldehyde Catalyzed by Dimethylamine

α,β-Unsaturated aldehydes are important building blocks for the synthesis of a wide range of chemicals, including polymers. The synthesis of these molecules from cheap feedstocks such as alkenes remains a scientific challenge, mainly due to the low reactivity of alkenes. Here we report a selective and metal-free access to α,β-unsaturated aldehydes from alkenes with formaldehyde. This reaction is catalyzed by dimethylamine and affords α,β-unsaturated aldehydes in yields of up to 80 %. By combining Density Functional Theory (DFT) calculations and experiments, we elucidate the reaction mechanism which is based on a cascade of hydride transfer, hydrolysis and aldolization reactions. The reaction can be performed under very mild conditions (30-50 °C), in a theoretically 100 % carbon-economical fashion, with water as the only by-product. The reaction was successfully applied to non-activated linear 1-alkenes, thus opening an access to industrially relevant α,β-unsaturated aldehydes from cheap and widely abundant chemicals at large scale.

Copper-Catalyzed Enantioselective C(sp3 )-SCF3 Coupling of Carbon-Centered Benzyl Radicals with (Me4 N)SCF3

In contrast with the well-established C(sp2 )-SCF3 cross-coupling to forge the Ar-SCF3 bond, the corresponding enantioselective coupling of readily available alkyl electrophiles to forge chiral C(sp3 )-SCF3 bond has remained largely unexplored. We herein disclose a copper-catalyzed enantioselective radical C(sp3 )-SCF3 coupling of a range of secondary/tertiary benzyl radicals with the easily available (Me4 N)SCF3 reagent. The key to the success lies in the utilization of chiral phosphino-oxazoline-derived anionic N,N,P-ligands through tuning electronic and steric effects for the simultaneous control of the reaction initiation and enantioselectivity. This strategy can successfully realize two types of asymmetric radical reactions, including enantioconvergent C(sp3 )-SCF3 cross-coupling of racemic benzyl halides and three-component 1,2-carbotrifluoromethylthiolation of arylated alkenes under mild reaction conditions. It therefore provides a highly flexible platform for the rapid assembly of an array of enantioenriched SCF3 -containing molecules of interest in organic synthesis and medicinal chemistry.

H2 O ⋅ B(C6 F5 )3 -Catalyzed para-Alkylation of Anilines with Alkenes Applied to Late-Stage Functionalization of Non-Steroidal Anti-Inflammatory Drugs

Anilines are core motifs in a variety of important molecules including medicines, materials and agrochemicals. We report a straightforward procedure that allows access to new chemical space of anilines via their para-C-H alkylation. The method utilizes commercially available catalytic H2 O ⋅ B(C6 F5 )3 and is highly selective for para-C-alkylation (over N-alkylation and ortho-C-alkylation) of anilines, with a wide scope in both the aniline substrates and alkene coupling partners. Readily available alkenes are used, and include new classes of alkene for the first time. The mild reaction conditions have allowed the procedure to be applied to the late-stage-functionalization of non-steroidal anti-inflammatory drugs (NSAIDs), including fenamic acids and diclofenac. The formed novel NSAID derivatives display improved anti-inflammatory properties over the parent NSAID structure.

Structure-reactivity analysis of novel hypervalent iodine reagents in S-vinylation of thiols

The transition-metal free S-vinylation of thiophenols by vinylbenziodoxolones (VBX) constituted an important step forward in hypervalent iodine-mediated vinylations, highlighting the difference to vinyliodonium salts and that the reaction outcome was influenced by the substitution pattern of the benziodoxolone core. In this study, we report several new classes of hypervalent iodine vinylation reagents; vinylbenziodazolones, vinylbenziodoxolonimine and vinyliodoxathiole dioxides. Their synthesis, structural and electronic properties are described and correlated to the S-vinylation outcome, shedding light on some interesting facets of these reagents.

Visible Light-Mediated Monofluoromethylation/Acylation of Olefins by Dual Organo-Catalysis

Monofluoromethyl (CH2F) motifs exhibit unique bioactivities and are considered privileged units in drug discovery. The radical monofluoromethylative difunctionalization of alkenes stands out as an appealing approach to access CH2F-containing compounds. However, this strategy remains largely underdeveloped, particularly under metal-free conditions. In this study, we report on visible light-mediated three-component monofluoromethylation/acylation of styrene derivatives employing NHC and organic photocatalyst dual catalysis. A diverse array of α-aryl-β-monofluoromethyl ketones was successfully synthesized with excellent functional group tolerance and selectivity. The mild and metal-free CH2F radical generation strategy from NaSO2CFH2 holds potential for further applications in fluoroalkyl radical chemistry.

Cuticular lipid profiles of selected species of cyclocephaline beetles (Melolonthidae, Cyclocephalini)

Neotropical cyclocephaline beetles, a diverse group of flower-loving insects, significantly impact natural and agricultural ecosystems. In particular, the genus Cyclocephala, with over 350 species, displays polymorphism and cryptic complexes. Lacking a comprehensive DNA barcoding framework, accessible tools for species differentiation are needed for research in taxonomy, ecology, and crop management. Moreover, cuticular hydrocarbons are believed to be involved in sexual recognition mechanisms in these beetles. In the present study we examined the cuticular chemical profiles of six species from the genus Cyclocephala and two populations of Erioscelis emarginata and assessed their efficiency in population, species, and sex differentiation. Overall we identified 74 compounds in cuticular extracts of the selected taxa. Linear alkanes and unsaturated hydrocarbons were prominent, with ten compounds between them explaining 85.6% of species dissimilarity. Although the cuticular chemical profiles efficiently differentiated all investigated taxa, only C. ohausiana showed significant cuticular profile differences between sexes. Our analysis also revealed two E. emarginata clades within a larger group of 'Cyclocephala' species, but they were not aligned with the two studied populations. Our research underscores the significance of cuticular lipid profiles in distinguishing selected cyclocephaline beetle species and contemplates their potential impact as contact pheromones on sexual segregation and speciation.

Aminothiolation of alkenes with azoles and Bunte salts

We have developed an intermolecular aminothiolation of simple olefins using Bunte salt as a thiolating agent. This protocol produces thiyl free radicals under PIDA oxidation conditions, eliminating the need for transition-metal catalysts. The method has a wide range of substrate applicability and is suitable for large-scale preparation and late-stage modification of drug molecules.

Hydrogenation of Terminal Alkenes Catalyzed by Air-Stable Mn(I) Complexes Bearing an N-Heterocyclic Carbene-Based PCP Pincer Ligand

Efficient hydrogenations of terminal alkenes with molecular hydrogen catalyzed by well-defined bench stable Mn(I) complexes containing an N-heterocyclic carbene-based PCP pincer ligand are described. These reactions are environmentally benign and atom economic, implementing an inexpensive, earth abundant non-precious metal catalyst. A range of aromatic and aliphatic alkenes were efficiently converted into alkanes in good to excellent yields. The hydrogenation proceeds at 100 °C with catalyst loadings of 0.25-0.5 mol %, 2.5-5 mol % base (KOt Bu) and a hydrogen pressure of 20 bar. Mechanistic insight into the catalytic reaction is provided by means of DFT calculations.

An Overview of Julia-lythgoe Olefination

Julia-Lythgoe olefination (or simply Julia olefination) is an olefination process between phenyl sulfones and aldehydes (or ketones) to give alkenes after alcohol functionalization and reductive elimination using sodium amalgam or SmI2. It is mainly used to synthesize E-alkenes and is a key step in numerous total syntheses of many natural products. This review exclusively deals with the Julia-Lythgoe olefination and concentrates mainly on the applications of this reaction in natural product synthesis covering literature up to 2021.

Dynamic changes to the plant cuticle include the production of volatile cuticular wax-derived compounds

The cuticle is a hydrophobic structure that seals plant aerial surfaces from the surrounding environment. To better understand how cuticular wax composition changes over development, we conducted an untargeted screen of leaf surface lipids from black cottonwood (Populus trichocarpa). We observed major shifts to the lipid profile across development, from a phenolic and terpene-dominated profile in young leaves to an aliphatic wax-dominated profile in mature leaves. Contrary to the general pattern, levels of aliphatic cis-9-alkenes decreased in older leaves following their accumulation. A thorough examination revealed that the decrease in cis-9-alkenes was accompanied by a concomitant increase in aldehydes, one of them being the volatile compound nonanal. By applying exogenous alkenes to P. trichocarpa leaves, we show that unsaturated waxes in the cuticle undergo spontaneous oxidative cleavage to generate aldehydes and that this process occurs similarly in other alkene-accumulating systems such as balsam poplar (Populus balsamifera) leaves and corn (Zea mays) silk. Moreover, we show that the production of cuticular wax-derived compounds can be extended to other wax components. In bread wheat (Triticum aestivum), 9-hydroxy-14,16-hentriacontanedione likely decomposes to generate 2-heptadecanone and 7-octyloxepan-2-one (a caprolactone). These findings highlight an unusual route to the production of plant volatiles that are structurally encoded within cuticular wax precursors. These processes could play a role in modulating ecological interactions and open the possibility for engineering bioactive volatile compounds into plant waxes.

Transition-Metal-Catalyzed Addition of Organosulfur Compounds to Alkynes and Alkenes: Catalysis and Catalyst Poisons

The addition of heteroatom compounds to alkynes and alkenes is an atom-efficient method of carbon-heteroatom bond formation and is widely used as a fundamental synthetic method for the construction of functional molecules. Nevertheless, examples of transition-metal-catalyzed addition reactions of group 16 heteroatom compounds to carbon-carbon unsaturated bonds have been limited due to the widespread belief that organic sulfur and selenium compounds are representative catalyst poisons. In recent decades, however, several seminal catalytic reactions of sulfur compounds have been developed, providing important insights into catalysis and poisons. Therefore, this paper focuses on the transition-metal-catalyzed addition of organosulfur compounds to alkynes and alkenes, gains comprehensive insights into the catalysis and catalyst poisons, and proposes concepts for the development of transition-metal-catalyzed reactions of group 16 heteroatom compounds.

Toxicological Assessment of Higher Olefins in OECD TG 422 Repeated Dose and Reproductive /Developmental Toxicity Screening Tests in Han Wistar Rats

Higher olefins (HO) are used primarily as intermediates in the production of other chemicals, such as polymers, fatty acids, plasticizer alcohols, surfactants, lubricants, amine oxides, and detergent alcohols. The potential toxicity of five HO (i.e., 1-Octene, Nonene, Decene, Hexadecene, and 1-Octadecene) with carbon ranging from C8 to C18 was examined in a combined repeated dose and reproduction/developmental toxicity screening study (OECD TG 422). These five HO were administered to Han Wistar rats by gavage at 0 (controls), 100, 300, and 1000 mg/kg bw/day. As a group of substances, adaptive changes in the liver (liver weight increase without pathological evidence), as well as increased kidney weight in male rats, were observed in HO with carbon numbers from C8 to C10. The overall systemic no observed adverse effect level (NOAEL) for all HO was determined at 1000 mg/kg bw/day. In the reproductive/developmental toxicity assessment, offspring viability, size, and weights were reduced in litters from females treated with Nonene at 1000 mg/kg bw/day. The overall no observed effects level (NOEL) for reproductive toxicity was considered to be 300 mg/kg bw/day for Nonene and 1000 mg/kg bw/day for the other four HO, respectively. These data significantly enrich the database on the toxicity of linear and branched HO, allowing comparison with similar data published on a range of linear and branched HO. Comparisons between structural class and study outcome provide further supportive data in order to validate the read-across hypothesis as part of an overall holistic testing strategy.

The Reactions of Alkenes with Phenyl-N-triflylimino-λ3-iodane: Solvent and Oxidant Impact

The reactions of alkenes with phenyl-N-triflylimino-λ3-iodane PhI=NTf (1) have been studied in different conditions. In methylene chloride, in the presence of N-halosuccinimides, the products of mono and bis-triflamidation were obtained. In MeCN, the product of bromotriflamidation (with NBS) with solvent interception or of bis-triflamidation (with NIS) is formed. The reaction with trans-stilbene in acetonitrile with NBS gave rise to cyclization to 2-methyl-4,5-diphenyl-1-triflyl-4,5-dihydro-1H-imidazole. In contrast, with NIS as an oxidant, both in CH2Cl2 and MeCN, the major product was 2,3-diphenyl-1-triflylaziridine formed in good yield. With NBS, aziridine is also formed but as a minor product, the major one being a mixture of diastereomers of the product of bromotriflamidation. The reaction of compound 1 with vinylcyclohexane in methylene chloride affords the mixtures of regioisomers of the products of halotriflamidation, whereas in acetonitrile, the products of solvent interception and cyclization to the imidazoline are formed. A mechanism explaining the formation of all isolated products is proposed.

One-Pot Synthesis of Polycyclic 4,5-Dihydropyridazine-3(2H)-ones by Inverse Electron-Demand Diels-Alder (IEDDA) Reactions from Alkenes

In the classical Inverse Electron-Demand Diels-Alder (IEDDA) reactions between alkenes and tetrazines, 4,5-dihydropyridazines are formed. 4,5-Dihydropyridazines are rapidly converted to the more energetically stable 1,4-dihydropyridazines by 1,3-prototropic isomerization. In this study, instead of 1,4-dihydropyridazines, 4,5-dihydropyridazine-3(2H)-ones were obtained as a result of IEDDA reactions between tetrazines with leaving groups at the 3,6-positions, and norbornene and barrelene-derived polycyclic alkenes in the presence of moisture in air or solvent. To show that this new method works not only on strained polycyclic alkenes but also on monocyclic and linear alkenes, the corresponding 4,5-dihydropyridazine-3(2H)-ones were obtained in high yields from the reactions performed with styrene and cyclopentene as well. The chemical structures of the polycyclic 4,5-dihydropyridazine-3(2H)-ones were determined by NMR and HRMS analyses. In addition, the exact structures of the polycyclic 4,5-dihydropyridazine-3(2H)-ones were also experimentally proven by converting them to pyridazine-3(2H)-ones known in the literature.

Analysis of Oleogel Volatile Profile Formation under Ultrasonic Treatment

Under certain conditions, ultrasonic treatment of certain foods and ingredients can contribute to the appearance of an extraneous odor, which is not usual for them, especially in fat-containing products. Since the food sector uses high-intensity ultrasound to control the crystallization of fats, the development of foreign smells and secondary fat oxidation products may impact the quality and safety of such items. In this work, we studied the volatile compounds' profiles of oleogels structured with individual fractions of beeswax using ultrasonic treatment. For this work, six samples of oleogels were obtained. Sunflower oil was used as a fatty base, and three fractions of beeswax were used as gelators: hydrocarbon fraction (>99%), monoester fraction (>95%), and a mixture fraction of wax di- and triesters (10.1%), free fatty acids (40.1%), and free fatty alcohols (49.8%). The influence of ultrasonic treatment on the properties of oleogels was assessed using light microscopy in polarized light, texture analysis, gas chromatography with flame ionization, and mass spectrometric detection. Ultrasonic treatment affected the crystallization of oleogels and led to the formation of smaller crystals. At the same time, sonication led to both an increase and a decrease in the firmness of oleogels, depending on the composition of the gelator. As regards volatile compounds, a total of 121 fragrant substances were identified in all samples, including such groups as alkanes, alkenes, alkadienes, alkynes, alkadiynes, alcohols, ketones, aldehydes, terpenes, alkyl alkane, and alkyl benzene derivatives. Ultrasonic treatment caused formation of new volatile unsaturated compounds. Some of them are known to have an unpleasant odor and thus might be responsible for the extraneous odor formation in studied fatty systems. Those were mainly (E)-2-octene, 1-heptene, 1,3-butadiene, and 1,3-octadiene in all oleogel samples. Sonicated samples B and C additionally had but-1-en-3-yne, pentenyne, and 1,3-butadiyne, whose odor can also be characterized as extraneous and distasteful. Several volatile compounds, supposed to be products of lipid oxidation, were also identified. Here we assume a reasonable approach is needed when selecting sonication conditions to prevent undesirable taste and flavor in oleogels and oleogel-based food products.

Visible-Light-Induced Three-Component Tetrafluoroethyl-heteroarylation of Alkenes with 1,1,2,2-Tetrafluoroethanesulfonyl Chloride and Quinoxalin-2(1H)-ones

1,1,2,2-Tetrafluoroethyl-containing compounds are valuable structures due to their unique physicochemical properties, which have increasing potential application in drug discovery. However, synthetic methods for preparing such compounds are rare. Herein, we report the first use of 1,1,2,2-tetrafluoroethanesulfonyl chloride to introduce the HCF2 CF2 group into organic molecules via a three-component, radical tetrafluoroethyl-heteroarylation of alkenes with readily available quinoxalin-2(1H)-ones. This method provides a new and facile approach for late-stage functionalization of potential biologically active molecules.

Axis-Unfixed Biphenylphosphine-Oxazoline Ligands: Design and Applications in Asymmetric Catalytic Reactions

The design and synthesis of chiral ligands plays an important role in asymmetric catalytic reactions. Over the past decades, various types of chiral phosphine-oxazolines (PHOX ligands) have been developed and have greatly advanced the field of asymmetric catalysis. Novel chiral PHOX ligand with an axis-unfixed biphenyl backbone, developed by our group, have shown interesting coordination behavior and excellent chiral inducing ability in various transition-metal-catalyzed asymmetric reactions. This personal account focuses on our developed axis-unfixed biphenylphosphine-oxazoline ligand (BiphPHOX), including an overview of its design and applications, which will provide inspiration for the exploration of novel ligands and related reactions.

Selective Synthesis of Monofluorinated Compounds Applying Amine/HF Reagents

For nucleophilic monofluorination, amine/HF reagents such as Et3 N⋅3HF, Pyr⋅9HF (Olah's reagent) and similar combinations belong to the most frequently used fluoride sources, whereupon the selectivity of these reagents can be very different depending of its acidity, the nucleophilicity of the fluoride equivalent, and the structure of the particular substrate. These reagents can be used safely in ordinary chemistry laboratories for nucleophilic substitution reactions by fluoride at sp3 -hybridized carbon centers. For ring opening reactions of epoxides, the regio- and stereoselectivity is very much depending of the nature of the epoxide and the acidity of the HF reagent favoring either SN 1 or SN 2 type reactions. Similarly, the outcome of halofluorination and similar reactions with sulfur or seleno electrophiles can be controlled by the particular combination of the electrophile and the fluoride source. Examples for the application of these reaction types for the synthesis of fluorine-containing analogues of natural products or biologically relevant compounds are in the focus of this personal account.

Photochemical Aminochlorination of Alkenes without the Use of an External Catalyst

The niche field of photochemistry offers opportunities that are not found in "traditional" ground state chemical pathways. Aminochlorinated derivatives are an interesting family of 1,2-difunctionalised compounds that provide access to a variety of natural products and pharmaceutical active substances. A practical, catalyst-free chloroamination protocol is described herein, providing access to intermediates of great importance, utilising mild and photochemical reaction conditions (370 nm), where N-chlorosulfonamides are used as both nitrogen and chlorine sources. A wide variety of olefins, decorated with a plethora of functional groups, was tested providing excellent results (28 examples, 18-88 % yield). Mechanistic studies (UV-Vis, control experiments and quantum yield measurement) were also performed.

Uncatalyzed Carbometallation Involving Group 13 Elements: Carboboration and Carboalumination of Alkenes and Alkynes

Carbometallation of alkenes and alkynes are powerful carbon-carbon bond-forming reactions. The use of compounds containing bonds between carbon and group 13 elements, particularly boron and aluminum, are particularly attractive because of the versatility of subsequent transformations. Uncatalyzed carboboration and carboalumination represent less common classes of reactions. This Short Review discusses uncatalyzed carboboration and carboalumination reactions of alkenes and alkynes, including the reaction design and mechanism.

Palladium-Catalyzed N-Alkenylation of N-Aryl Phosphoramidates with Alkenes

Versatile and concise Pd-catalyzed oxidative N-alkenylation of N-aryl phosphoramidates with alkenes is described in this study, a reaction that is of great significance but surprisingly unexploited. The transformation proceeds under mild reaction conditions, using O₂ as a green oxidant and TBAB as an effective additive. An efficient catalytic system allows a variety of drug-related substrates to participate in these transformations, which is of great interest in the drug discovery and development of phosphoramidates.

Dear Editor, Please find enclosed a manuscript entitled:PtII-N-Heterocyclic Carbene Complexes in Solvent-Free Alkene Hydrosilylation

The structural characterization and catalytic activity of a series of platinum(II) complexes, bearing N-heterocyclic carbenes (NHC) as supporting ligands, are reported. The study presents a structure-activity relationship within a group of pre-catalysts, and mechanistic insights into the catalyst activation step. An exceptional catalytic performance of one of the complexes is presented and an attractive solvent-free and open-to-air alkene hydrosilylation protocol, featuring efficient platinum removal, are disclosed.

Functionalization of Olefinic C-H Bonds by an Aryl-to-Vinyl 1,4-Nickel Migration/Reductive Coupling Sequence

An attractive approach to selective functionalization of remote C-H bonds is a metal/hydride shift/cross-coupling reaction sequence. Complimentary to the heavily exploited 1,2-nickel/hydride shift along an sp3 chain, a chain-walking process, the 1,4-nickel/hydride shift along an sp2 chain is more complex. Here we report an unprecedented aryl-to-vinyl 1,4-nickel/hydride shift reaction, in which the migratory alkenylnickel species generated in situ is selectively trapped by one of various coupling partners, such as isocyanates, alkyl bromides, aryl chlorides or alkynyl bromides, allowing regio- and stereoselective access to trisubstituted alkenes. In contrast to the well-reported ipso-aryl coupling reactions, this strategy provides remote alkenyl C-H functionalized products with good yield and with excellent chemo-, regio- and E/Z-selectivity.

Advances in Selective Electrocatalytic Hydrogenation of Alkynes to Alkenes

Selective electrochemical hydrogenation of alkynes to alkenes under ambient conditions is a promising alternative to the traditional energy-intensive and high-cost thermocatalytic hydrogenation. However, the systematic summary on the electrocatalysts and electrolyzers remains lacked. Herein, we demonstrate a comprehensive review about recent achievements in the electrocatalysts including noble metal and non-noble-metal materials. Several effective strategies of catalyst design were developed to improve alkyne conversion, and alkene selectivity, for example, accelerating the formation of active hydrogen species, enhancing alkyne adsorption and suppressing the side reactions. Furthermore, the advantages and disadvantages of various electrolyzers are systematically discussed. Accordingly, major challenges and future trends in this field are proposed.

Three-Component Perfluoroalkylvinylation of Alkenes Enabled by Dual DBU/Fe Catalysis

Herein, a simple and efficient strategy that involves dual 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/iron-catalyzed alkene perfluoroalkylvinylation by using perfluoroalkyl iodides and 2-aminonaphthalene-1,4-diones as coupling partners is demonstrated. In terms of the developed catalytic system, various styrenes and aliphatic alkenes are well-tolerated, leading to the accurate preparation of perfluoroalkyl-containing 2-aminonaphthalene-1,4-diones in excellent regioselectivity. Moreover, the protocol can be readily applied in late-stage modifications of natural products and pharmaceuticals. The title reactions are featured by easily accessible and inexpensive catalysts and substrates, broad substrate applicability, and mild reaction conditions. Mechanistic investigations reveal a tandem C-I cleavable alkylation and C-C vinylation enabled by cooperative DBU/iron catalysis.

A Supported Palladium Phosphide Catalyst for the Wacker-Tsuji-Oxidation of Styrene

The substitution of pure metal particles by metal phosphides in catalysis represents a promising opportunity to lower the required metal quantity in the context of a sustainable use of metal resources. Herein we show the synthesis of palladium phosphide, Pd₃ P, supported on silica, which is tested as catalyst for the Wacker-Tsuji-oxidation of styrene to acetophenone. The synthesized catalyst is characterized by PXRD, SEM-EDX, FTIR, ICP-AES and XPS measurements. Four different reaction systems are investigated in this study including different co-catalysts and reaction media. Conversions of styrene up to 95 % with a selectivity of 73 % towards acetophenone are observed using Pd₃ P/SiO₂ as catalyst, CuCl₂ as co-catalyst and O₂ as oxidant. An enhanced selectivity up to 100 % towards acetophenone is obtained in other reaction systems. The use of Pd₃ P/SiO₂ leads to an optimized selectivity and conversion in the oxidation reaction in comparison with the purely Pd-based system Pd/SiO₂ . These results give an insight on how the incorporation of phosphorus has a great effect on the performance of heterogeneous catalysts.

Visible-Light-Promoted Catalyst-Free Oxyarylation and Hydroarylation of Alkenes with Carbon Dioxide Radical Anion

Visible-light-mediated oxyarylation and hydroarylation of alkenes with aryl halides using formate salts as the reductant and hydrogen source under ambient conditions were developed. These protocols represent rare catalyst-free examples of the realization of such transformations. Using styrenes as substrates, oxyarylation could occur smoothly. Whereas, hydroarylation proceeds employing electron deficient alkenes. Moreover, dehalogenation proceeds successfully in the absence of alkenes. We expected that this method could provide a valuable strategy for the functionalization of aryl halides.

Polyfunctional catalysis in conversion of light alkenes

Light alkenes are among the main petrochemical intermediate products, the consumption of which is steadily growing. Using ethylene as an example, the possibilities of using polyfunctional heterogeneous catalysts for carrying out practically important reactions of its oligomerization, alkylation, and metathesis were considered. Particular attention was paid to catalysts for the conversion of ethylene to propylene.

Access to cyclopropanes with geminal trifluoromethyl and difluoromethylphosphonate groups

A synthetic route to the bench-stable fluorinated masked carbene reagent diethyl 2-diazo-1,1,3,3,3-pentafluoropropylphosphonate, bearing a trifluoromethyl and a difluoromethyl group is reported for the first time. Its application in CuI-catalyzed cyclopropanation reactions with aromatic and aliphatic terminal alkenes under mild reaction conditions is demonstrated. In total, sixteen new cyclopropanes were synthesized in good to very good yields.

B(C6 F5 )3 -Catalyzed E-Selective Isomerization of Alkenes

Herein, we report the B(C₆ F₅ )₃ -catalyzed E-selective isomerization of alkenes. The transition-metal-free method is applicable across a diverse array of readily accessible substrates, giving access to a broad range of synthetically useful products containing versatile stereodefined internal alkenes. The reaction mechanism was investigated by using synthetic and computational methods.

Stereoselective Semi-Hydrogenations of Alkynes by First-Row (3d) Transition Metal Catalysts

The chemo- and stereoselective semi-hydrogenation of alkynes to alkenes is a fundamental transformation in synthetic chemistry, for which the use of precious 4d or 5d metal catalysts is well-established. In mankind's unwavering quest for sustainability, research focus has considerably veered towards the 3d metals. Given their high abundancy and availability as well as lower toxicity and noxiousness, they are undoubtedly attractive from both an economic and an environmental perspective. Herein, we wish to present noteworthy and groundbreaking examples for the use of 3d metal catalysts for diastereoselective alkyne semi-hydrogenation as we embark on a journey through the first-row transition metals.

Highly Z-Selective Horner-Wadsworth-Emmons Olefination Using Modified Still-Gennari-Type Reagents

In this report, new, easily accessible reagents for highly Z-selective HWE reactions are presented. Alkyl di-(1,1,1,3,3,3-hexafluoroisopropyl)phosphonoacetates, structurally similar to Still–Gennari type reagents, were tested in HWE reactions with a series of various aldehydes. Very good Z-selectivity (up to a 98:2 Z:E ratio) was achieved in most cases along with high yields. Application of the new reagents may be a valuable, practical alternative to the well-established Still–Gennari or Ando Z-selective carbonyl group olefination protocols.

Palladium-Catalyzed Cascade Cyclization/Alkylation of Oxime Ethers: Assembly of 4-Alkylisoxazoles by "Chain-Walking" Strategy

A reliable and efficient palladium-catalyzed cascade cyclization/alkylation of oxime ethers with unactivated alkenes is described, affording a whole variety of structurally diverse isoxazole derivatives in moderate to good yields with excellent functional group compatibility. Ionic liquid [Aeim]Br not only acts as an environmentally friendly solvent but also acts as an accelerating agent to provide excess bromine source to eliminate bromomethane from oxime ethers. More importantly, the use of "chain-walking" strategy provides a novel methodology in organic synthesis to rapid generation of molecular complexity from readily available starting materials.

Azole-Directed Cobalt-Catalyzed Asymmetric Hydrogenation of Alkenes

The azole-directed cobalt-catalyzed asymmetric hydrogenation of alkenes has been developed with high efficiency. With this approach, chiral pyrazole compounds were obtained in quantitative yields and excellent enantioselectivities (up to 99 % ee) under mild conditions, and the hydrogenation was conducted on a gram scale with up to 2000 TON. Several useful applications were demonstrated including the convenient introduction of β-chirality to a drug intermediate containing an azole ring.

Ni-Catalyzed Regio- and Stereoselective Alkylarylation of Unactivated Alkenes in γ,δ-Alkenylketimines

We disclose a Ni-catalyzed vicinal alkylarylation of unactivated alkenes in γ,δ-alkenylketimines with aryl halides and alkylzinc reagents. The reaction produces γ-C(sp3)-branched δ-arylketones with the construction of two new C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds. Electron-deficient alkenes play crucial dual roles as ligands to stabilize reaction intermediates and to increase catalytic rates for the formation of C(sp3)-C(sp3) bonds. This alkene alkylarylation reaction is also effective for secondary alkylzinc reagents and internal alkenes, and proceeds with a complete regio- and stereocontrol, affording products with up to three contiguous all-carbon all-cis secondary stereocenters.

Chiral Hemilabile P,N-Ligand-Assisted Gold Redox Catalysis for Enantioselective Alkene Aminoarylation

Enantioselective, intermolecular alkene arylamination was achieved through gold redox catalysis. Screening of ligands revealed chiral P,N ligands as the optimal choice, giving alkene aminoarylation with good yields (up to 80 %) and excellent stereoselectivity (up to 99 : 1 er). As the first example of enantioselective gold redox catalysis, this work confirmed the feasibility of applying a chiral ligand at the gold(I) stage, with the stereodetermining step (SDS) at the gold(III) intermediate, thus opening up a new way to conduct gold redox catalysis with stereochemistry control.

Recent Advances in 1,2-Amino(hetero)arylation of Alkenes

Alkene amino(hetero)arylation presents a highly efficient and straightforward strategy for direct installation of amino groups and heteroaryl rings across a double bond simultaneously. An extensive array of practical transformations has been developed via alkene difunctionalization approach to access a broad range of medicinally valuable (hetero)arylethylamine motifs. This review presents recent progress in 1,2-amino(hetero)arylation of alkenes organized in three different modes. First, intramolecular transformations employing C, N-tethered alkenes will be introduced. Next, two-component reactions will be discussed with different combination of precursors, N-tethered alkenes and external aryl precursor, C-tethered alkenes and external amine precursor, or C, N-tethered reagents, and alkenes. Last, three-component intermolecular amino(hetero)arylation reactions will be covered.

Visible Light-Induced Hydrosilylation of Electron-Deficient Alkenes by Iron Catalysis

Herein, we reported a method for iron-catalyzed, visible-light-induced hydrosilylation reactions of electron-deficient alkenes to produce value-added silicon compounds. Alkenes bearing functional groups with different steric properties were suitable substrates, as were derivatives of structurally complex natural products. Mechanistic studies showed that chlorine radicals generated by iron-catalyzed ligand-to-metal charge transfer in the presence of lithium chloride promoted the formation of silyl radicals.

Recent progress in aryltrifluoromethylation reactions of carbon-carbon multiple bonds

Due to the increasing relevance of fluorine-containing organic molecules in drug design, the synthesis of organofluorine compounds has gained high significance in synthetic organic chemistry. Trifluoromethylative difunctionalizations of carbon-carbon multiple bonds, with the simultaneous incorporation of a CF 3 group and another functional element, have considerable potential. Because of the high importance of carbon-carbon bond-forming reactions in organic synthesis, carbotrifluoromethylations and, in particular, aryltrifluoromethylations or heteroaryltrifluoromethylations are considered to be increasing fields of synthetic organic chemistry. The aim of the current review is to summarize recent developments of aryltrifluoromethylation or heteroaryltrifluoromethylation reactions.

Chemical Composition of Essential Oil from Four Sympatric Orchids in NW-Italy

Orchidaceae is a flowering plant family worldwide distributed known for producing volatile organic compounds (VOCs) which can act as olfactory signals for pollinators. Despite the importance of VOCs in the different reproductive strategies, in the literature there are only a few publications on the characterization of orchids' volatile profiles. In this study, the essential oils from fresh inflorescences of sympatric orchids Anacamptis morio, Himantoglossum robertianum, Ophrys sphegodes and Orchis purpurea, naturally growing in Piedmont (Italy) were isolated by steam distillation and characterized by GC/FID and GC/MS. A number of compounds were identified, with a peculiar distribution in the species: alcohols (range 16.93-50.60%), from which p-cresol (range 12.75-38.10%) was the most representative compound; saturated hydrocarbons (range 5.81-59.29%), represented by pentacosane (range 2.22-40.17%) and tricosane (range 0.78-27.48%); long-chain monounsaturated hydrocarbons (range 0.29-5.20%) represented by 9-pentacosene, 11-tricosene, and 1-heneicosene. The structure of positional isomers in linear alkenes was elucidated by derivatization with dimethyl disulfide and MS fragmentation patterns. Coumarin (68.84%) was the dominant compound in O. purpurea and was detected in lower concentrations (range 0.21-0.26%) in the other taxa. These volatile compounds may represent a particular feature of these plant species and play an essential role in pollinator interaction.

anti-Markovnikov Iodofluorination of Alkenes

The fluorination of alkenes with electrophilic N-F type reagents usually occurs through a Markovnikov-type addition, and the anti-Markovnikov-type addition may require the use of a transition metal catalyst or an expensive catalyst. Herein we describe a convenient anti-Markovnikov iodofluorination of alkenes with Selectfluor/ nBu4NI. A wide substrate scope and good functional group tolerance were observed. The process allows for the construction of various C-F bonds, especially tertiary C-F bonds. The remarkable features make this protocol attractive, including convenient operations, simple reaction conditions, and the installation of an iodine atom which provides possibilities for further transformations.

Direct 1,2-Dicarbonylation of Alkenes towards 1,4-Diketones via Photocatalysis

1,4-Dicarbonyl compounds are intriguing motifs and versatile precursors in numerous pharmaceutical molecules and bioactive natural compounds. Direct incorporation of two carbonyl groups into a double bond at both ends is straightforward, but also challenging. Represented herein is the first example of 1,2-dicarbonylation of alkenes by photocatalysis. Key to success is that N(n-Bu)₄ ⁺ not only associates with the alkyl anion to avoid protonation, but also activates the α-keto acid to undergo electrophilic addition. The α-keto acid is employed both for acyl generation and electrophilic addition. By tuning the reductive and electrophilic ability of the acyl precursor, unsymmetric 1,4-dicarbonylation is achieved for the first time. This metal-free, redox-neutral and regioselective 1,2-dicarbonylation of alkenes is executed by a photocatalyst for versatile substrates under extremely mild conditions and shows great potential in biomolecular and drug molecular derivatization.

The Electrochemical cis-Chlorination of Alkenes

The first example for the electrochemical cis‐dichlorination of alkenes is presented. The reaction can be performed with little experimental effort by using phenylselenyl chloride as catalyst and tetrabutylammoniumchloride as supporting electrolyte, which also acts as nucleophilic reagent for the S_N2‐type replacement of selenium versus chloride. Cyclic voltammetric measurements and control experiments revealed a dual role of phenylselenyl chloride in the reaction. Based on these results a reaction mechanism was postulated, where the key step of the process is the activation of a phenylselenyl chloride‐alkene adduct by electrochemically generated phenylselenyl trichloride. Like this, different aliphatic and aromatic cyclic and acyclic alkenes were converted to the dichlorinated products. Thereby, throughout high diastereoselectivities were achieved for the cis‐chlorinated compounds of >95 : 5 or higher.

Green Process Design for Reductive Hydroformylation of Renewable Olefin Cuts for Drop-In Diesel Fuels

CO₂ -neutral fuels are a way to cleaner and more sustainable mobility. Utilization of bio-syngas via Fischer-Tropsch (FT) synthesis represents an interesting route for the production of tailormade biofuels. Recent developments in FT catalyst research led to olefin-enriched products, enabling the synthesis of alcohol-enriched fuels by reductive hydroformylation of the C=C bond. Several alcohols have already proven to be suitable fuel additives with favorable combustion behavior. Here, a hydroformylation-hydrogenation sequence of FT-olefin-paraffin mixtures was investigated as a potential route to alcohols. A liquid-liquid biphasic system with a rhodium/3,3',3''-phosphanetriyltris(benzenesulfonic acid) trisodium salt (TPPTS) catalyst system was chosen for effective catalyst recycling. After optimizing reaction conditions with a model substrate consisting of 1-octene and n-heptane the conversion of an actual olefin-containing C₅ -C₁₀  FT product fraction to alcohols in continuously operated processes for 37 h was achieved with a total turnover number of 23679.

Recent Advances on the Halo- and Cyano-Trifluoromethylation of Alkenes and Alkynes

Incorporation of fluorine into organic molecules is a well-established strategy in the design of advanced materials, agrochemicals, and pharmaceuticals. Among numerous modern synthetic approaches, functionalization of unsaturated bonds with simultaneous addition of trifluoromethyl group along with other substituents is currently one of the most attractive methods undergoing wide-ranging development. In this review article, we discuss the most significant contributions made in this area during the last decade (2012−2021). The reactions reviewed in this work include chloro-, bromo-, iodo-, fluoro- and cyano-trifluoromethylation of alkenes and alkynes.

Carboboration-Driven Generation of a Silylium Ion for Vinylic C-F Bond Functionalization by B(C6 F5 )3 Catalysis

Strong main-group Lewis acids such as silylium ions are known to effectively promote heterolytic C(sp³ )-F bond cleavage. However, carrying out the C(sp² )-F bond transformation of vinylic C-F bonds has remained an unmet challenge. Herein, we describe our development of a new and simple strategy for vinylic C-F bond transformation of α-fluorostyrenes with silyl ketene acetals catalyzed by B(C₆ F₅ )₃ under mild conditions. Our theoretical calculations revealed that a stabilized silylium ion, which is generated from silyl ketene acetals by carboboration, cleaves the C-F bond of α-fluorostyrenes. A comparative study of α-chloro or bromostyrenes demonstrated that our reaction can be applied only to α-fluorostyrenes because the strong silicon-fluorine affinity facilitates an intramolecular interaction of silylium ions with fluorine atom to cleave the C-F bond. A broad range of α-fluorostyrenes as well as a range of silyl ketene acetals underwent this C-F bond transformation.

Hydroboration of Terminal Alkenes and trans-1,2-Diboration of Terminal Alkynes Catalyzed by a Manganese(I) Alkyl Complex

A Mn^I‐catalyzed hydroboration of terminal alkenes and a 1,2‐diboration of terminal alkynes with pinacolborane (HBPin) is described. For alkenes, anti‐Markovnikov hydroboration takes place; for alkynes the reaction proceeds with excellent trans‐1,2‐selectivity. The most active pre‐catalyst is bench‐stable alkyl bisphosphine Mn^I complex fac‐[Mn(dippe)(CO)₃(CH₂CH₂CH₃)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn–alkyl bond to yield an acyl intermediate, which undergoes B−H bond cleavage of HBPin (for alkenes) and rapid C−H bond cleavage (for alkynes), forming the active Mn^I boryl and acetylide catalysts [Mn(dippe)(CO)₂(BPin)] and [Mn(dippe)(CO)₂(C≡CR)], respectively. A broad variety of aromatic and aliphatic alkenes and alkynes was efficiently and selectively borylated. Mechanistic insights are provided based on experimental data and DFT calculations revealing that an acceptorless reaction is operating involving dihydrogen release.