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We have developed the Rh‐catalyzed enantioselective [2+2+2] cycloaddition of homopropargyl enamides (tosylamide‐tethered 1,6‐enynes) with alkynes to construct tetrahydroindole skeletons found in natural alkaloids and pharmaceuticals. This cycloaddition proceeds at room temperature in high yields and regio‐ and enantioselectivity with a broad substrate scope. The preparative scale reaction followed by substituent conversion on the nitrogen atom and the diastereoselective [4+2] cycloaddition with singlet O2 affords hexahydroindole‐diols bearing three stereogenic centers and variable substituents on the nitrogen. Mechanistic studies have revealed that the substituents of the enynes change the ratio of intramolecular and intermolecular rhodacycle formation when using terminal alkynes, varying the ee values of the cycloadducts. [ABSTRACT FROM AUTHOR]

Dearomative cycloadditions are powerful synthetic transformations utilizing aromatic compounds for cycloaddition reactions. They have been extensively applied to the synthesis of biologically relevant compounds not only because of the complexity generated from simplicity but also the atom‐ and step‐economy. For the most studied yet challenging benzene ring systems, ortho‐ and para‐cycloadditions have been realized both photochemically and thermally, while the meta‐cycloadditions are still limited to the photochemical processes tracing back to the 1960s. Herein, we for the first time realized the thermal cycloadditions of benzene rings with alkenes in a meta fashion via Wheland intermediates. A broad spectrum of readily available C(sp2)‐rich aniline‐tethered enynes were transformed into C(sp3)‐rich 3D complex polycyclic architectures simply by stirring in TFA. Moreover, the reaction could be performed in gram‐scales and the products could be diversely elaborated. [ABSTRACT FROM AUTHOR]

Green chemistry strives for sustainability at the molecular level and is gaining increasing relevance in the development of chemical reactions. The haloalkynylation reaction is a highly atom–economical C−C coupling reaction that was previously only achieved using transition metal catalysts. It enables the introduction of an alkyne unit and a halogen atom into the target molecule. Herein, we present a haloalkynylation reaction catalyzed by indium(III) halides. The use of indium(III) bromide as a catalyst leads exclusively to the cis addition products with yields up to 86 %. In addition, iodoacetylenes can be applied for the first time for the haloalkynylation reaction of internal alkynes which is an important step forward in the development of industrially relevant and sustainable catalysts. In contrast to gold catalysis, which proceeds via a similar mechanism, the use of alkyl‐substituted haloacetylenes as reagents is also possible. Based on 13C labeling experiments and quantum chemical calculations, we postulate two possible mechanisms for the indium(III)‐catalyzed haloalkynylation reactions. [ABSTRACT FROM AUTHOR]

Alkenes constitute an enabling motif in organic synthesis, as they can be functionalized to form highly substituted molecules. Z‐alkenes are generally challenging to access due to the thermodynamic preference for the formation of E‐alkenes compared to Z‐alkenes. Dehydrogenation methodologies to selectively form Z‐alkenes have not yet been reported. Herein, we report a Z‐selective, propargylic dehydrogenation that provides 1,3‐enynes through the invention of a Co‐catalyzed oxidation system. Observation of a kinetic isotope effect (KIE) revealed that deprotonation of the propargylic position is the rate limiting step. Additionally, isomerization experiments were conducted and confirmed that the observed Z‐selectivity is a kinetic effect. A proposed stereomechanistic model for the Z‐selectivity is included. [ABSTRACT FROM AUTHOR]

Herein, we present catalyst‐regulated switchable site‐selective hydrosilylation of enynes, which are suitable for a wide range of alkyl and aryl substituted polar enynes and exhibit excellent functional group compatibility. Under the optimized conditions, silyl groups can be precisely installed at various positions of 1,3‐dienes. While α‐ and γ‐silylation products were obtained under platinum‐catalytic systems, β‐silylation products were delivered with [Cp*RuCl]4 as catalyst. This process lead to the formation of 1,3‐dienoates with diverse substitutions, which would pose challenges with other methodologies. [ABSTRACT FROM AUTHOR]

Trialkyl phosphines PMe3 and PEt3 catalyze the 1,2‐cis‐diboration of 1,3‐butadiynes to give 1,2‐diboryl enynes. The products were utilized to synthesize 1,1,2,4‐tetraaryl enynes using a Suzuki‐Miyaura protocol and can readily undergo proto‐deborylation. [ABSTRACT FROM AUTHOR]

Herein, a palladium-catalyzed regioselective alkynylation, esterification, and amination of allylic gem-difluorides via C--F bond activation/transmetallation/β-C elimination or nucleophilic attack has been achieved. This innovative protocol showcases an extensive substrate range and operates efficiently under mild reaction conditions, resulting in high product yields and Z-selectivity. Particularly noteworthy is its exceptional tolerance towards a wide array of functional groups. This developed methodology provides effective and convenient routes to access a diverse array of essential fluorinated enynes, esters and amines. [ABSTRACT FROM AUTHOR]

We identify the dominant structures of the intermediates of gold(I)‐catalyzed cyclizations of 1,5‐enynes and 1,5‐allenenes through computational analysis as gold(I) cyclopropylcarbenes, endocyclic vinylgold complexes and previously unreported non‐classical carbocationic minima. In contrast to 1,6‐enynes, the exocyclic carbocations are found to be less stable. Cyclopropylcarbene structures are consistently favoured as the most stable intermediates for all studied substitution patterns. We validate the computational methods used by using DLPNO‐CCSD(T) energies as a benchmark, indicating that the B3LYP‐D3 and M06‐D3 functionals are most accurate for energy determination, while NPA charges are mostly insensitive to functional. The evolution of a 1,6‐enyne in a single‐cleavage or double‐cleavage rearrangement is attributed to the barrierless evolution of a common cyclopropyl–gold(I) carbocation non‐stationary geometry. Our findings provide insights into reaction pathways and substrate dependence of the cycloisomerization processes. [ABSTRACT FROM AUTHOR]

Tandem cycloisomerization reactions of functionalized 1,6‐enynes under indium(III) catalysis are described. This atom‐economic transformation proceeds smoothly with 5‐exo‐dig regioselectivity using commercial In(III) halides and 1,6‐enynes furnished with alcohol, carboxylic acid or amine functional groups to give bicyclic structures in good yields and diastereoselectivities. The reaction with enynals involves a three–step mechanism to give an oxatricycle and a conjugated 1,3‐diene. In the absence of the internal nucleophile the enyne cycloisomerization evolves through a skeletal rearrangement or a cyclopropanation reaction after the regioselective 5‐exo‐dig cyclization. The 1,6‐enyne cycloisomerization is stereospecific and the stereoselectivity appears to be independent of the internal nucleophile. Experimental data support a common reaction mechanism involving an initial alkyne electrophilic π‐coordination of In(III) followed by Markovnikov electrophilic alkene addition and ring‐closure by nucleophilic attack. DFT studies hold up a stepwise mechanism involving the formation of a chiral non‐classical carbocation intermediate that determines the diastereoselectivity of this tandem cycloisomerization reaction. [ABSTRACT FROM AUTHOR]

In this study we present a method for functionalizing C60 through a Rh‐catalyzed cyclization reaction with 1,6‐enynes, resulting in the formation of a fused bicyclic structure. Additionally, fullerene derivatives are further functionalized through regioselective photooxygenation reactions. Our DFT calculations reveal two distinct reaction pathways: one involving rhodium‐catalyzed cycloisomerization of the enyne followed by Diels‐Alder with C60, and the other featuring a rhodium‐catalyzed [2+2+2] cycloaddition of enyne and C60 followed by isomerization. Surprisingly, both pathways exhibit nearly identical energy barriers. However, experimental tests indicate that the predominant pathway varies depending on the substitution motifs of the substrates. [ABSTRACT FROM AUTHOR]

Reaching the formidable C−H corners has been one of the top priorities of organic chemists in the recent past. This prompted us to disclose herein a vicinal annulation of 2‐iodo benzoates, indoles, and carbazoles with N‐embedded 1,6‐enynes through 7‐/8‐membered palladacycles. The relay does not require the assistance of any directing group, leading to multicyclic scaffolds, which are readily diversified to an array of adducts (with new functional tethers and/or three contiguous stereocenters), in which we showcase a rare benzylic mono‐oxygenation. [ABSTRACT FROM AUTHOR]

Propynylidene derivatives of dimethyl malonate and Meldrumʼs acid, as well as cross-conjugated enynones, containing Me3Si, Et3Si, and t-BuMe2Si groups reacted with 4-methyl-, 4-methoxy-, and 4-chloro-benzenethiol under basic conditions to give the corresponding addition products with buta-1,3-diene and penta-1,4-dien-3-one fragments with high stereoselectivity. The thiylation products of enyne derivatives of dimethyl malonate and Meldrumʼs acid retain the trialkylsilyl group, whereas the addition of benzenethiols to 5-(tri-alkylsilyl)-1-phenylpent-1-en-4-yn-3-ones is accompanied by desilylation. Some mechanistic features of the described reactions have been established, and methods for the stereoselective synthesis of sulfur-containing polyunsaturated compounds have been developed. [ABSTRACT FROM AUTHOR]

We established a strategy for the copper‐catalyzed three‐component 1,4‐phosphinoylcyanation of 1,3‐enynes with diarylphosphine oxides and trimethylsilyl cyanide. The reaction produced various tetrasubstituted phosphinoyl‐ and cyano‐containing allenes with high functional group compatibilities in good yields under mild reaction conditions. A preliminary reaction mechanism involving the formation of phosphinoyl radicals and their regioselective addition to 1,3‐enynes was also proposed. [ABSTRACT FROM AUTHOR]

Studies into the ring‐closing enyne metathesis of a series of nine sulfone containing enynes is described. The readily accessible sulfone substrates were shown to undergo cyclisation to form 3‐subsituted 2,5‐dihydrothiophene 1,1‐dioxides (sulfolenes) and one 3,6‐dihydro‐2H‐thiopyran 1,1‐dioxide. The success of this process depended on the substrate's substitution pattern. Moderate to good yields of the products were obtained when the ene component was monosubstituted and it was found that the reactions proceeded most efficiently using the 2nd generation Grubbs catalysts, at elevated temperatures. [ABSTRACT FROM AUTHOR]

Two different classes of stereoselective cyclizations have been developed using a chiral auxiliary approach with commercially available [JohnPhosAu(MeCN)SbF6] as catalyst. First, a stereoselective cascade cyclization of 1,5‐enynes was achieved using the Oppolzer camphorsultam as chiral auxiliary. In this case, a one‐pot cyclization‐hydrolysis sequence was developed to directly afford enantioenriched spirocyclic ketones. Then, the stereoselective alkoxycyclization of 1,6‐enynes was mediated by an Evans‐type oxazolidinone. A reduction‐hydrolysis sequence was selected to remove the auxiliary to give enantioenriched β‐tetralones. DFT studies confirmed that the steric clash between the chiral auxiliary and alkene accounts for the experimentally observed diastereoselective cyclization through the Si face. [ABSTRACT FROM AUTHOR]

Palladium hydrides are traditionally employed in hydrofunctionalization (i.e. monofunctionalization) of conjugated dienes and enynes, owning to its facile protic hydropalladation of electron‐rich (or neutral) unsaturated bonds. Herein, we report a mild PdH‐catalyzed difunctionalization of conjugated dienes and enynes. This protocol is enabled by the chemoselectivity switch of the initial hydropalladation step achieved by visible light enhancement of hydricity of PdH species. This method allows for cascade annulation of dienes and enynes with various easily available and abundant substrates, such as acrylic acids, acrylic amides, and Baylis–Hillman adducts, toward a wide range of alkenyl or alkynyl lactones, lactams, and tetrahydrofurans. This protocol also provides an easy access to complex spiro‐fused tricyclic frameworks. [ABSTRACT FROM AUTHOR]

A novel and efficient palladium‐catalyzed regioselective and stereodivergent ring‐closing reaction of aminoenynes with aldehydes and boronic acids or hydrosilane is developed. This three‐component reaction allows for the modular synthesis of a series of exocyclic 1,3‐dienes bearing 5‐ to 8‐membered saturated N‐heterocycles. The reactions utilize a simple Pd‐catalyst and work with broad range of aminoenynes, aldehydes and organometallic reagents under mild reaction conditions. The products represent useful intermediates for chemical synthesis due to the versatility of the conjugated diene. Preliminary mechanistic details of the method are also revealed. [ABSTRACT FROM AUTHOR]

(E)-1-aryl-2,4-bis(trimethylsilyl)but-1-en-3-ynes readily undergo protodesilylation and subsequent aerobic, copper-free Sonogashira cross-coupling with aryl halides to form (E)-1,4-diaryl-2-(trimethylsilyl)but-1-en-3-ynes. The proposed one-pot, two-step approach allows access to the isomers containing aryl substituents in mutual syn positions. The resulting 2-silyl enynes can be further converted by proto- or halodesilylation.

The influence of the P–M–P bite angle in diphosphine ligands on selectivity has been observed in various catalytic reactions. A better understanding of the ligand bite angle concept is important for the rational design of efficient catalytic systems. In the present work, the mechanism of cobalt-catalyzed C–H functionalization of aldehydes with enynes and how the diphosphine ligands alter regioselectivity were investigated by density functional theory (DFT) calculations. The catalytic cycle is initiated by the oxidative cyclization of enynes rather than the oxidative addition of aldehydes. Regioselectivity arises from competing σ-bond metathesis and migratory insertion steps, in which the steric effects of diphosphine ligands are the dominant factors influencing the activation barriers. The calculations indicate that σ-bond metathesis is more challenging and its feasibility is highly dependent on the ligand bite angle. The improved mechanistic understanding will enable further design of transition-metal-catalyzed selective cyclization reactions. [ABSTRACT FROM AUTHOR]

The enantioselective catalytic cascade involving Tsuji–Trost allylation has provided a viable strategy for the construction of multiple asymmetric C–C and C–X centres and numerous methods have been developed around it for the synthesis of various vital scaffolds. The synthetic utility of this strategy was enhanced by replacing the customary allyl acetates with ethylene diacetates/dicarbonates, vinyl epoxides, vinyl oxetanes, vinyl ethylene carbonates, vinyl cyclopropanes, enynes, and dienes using transition-metal catalysis. One more milestone was achieved when metallaphotocatalysis provided the necessary platform for these cascades by using a cheaper metal. This review will provide a summary of these enantioselective catalytic cascades from 2015. [ABSTRACT FROM AUTHOR]

Described herein is a visible‐light photoredox‐catalyzed regioselective 1,4‐hydroalkylation of 1,3‐enynes. Various of di‐ and tri‐substituent allenes were really accessible under the present reaction conditions. The visible‐light photoredox activation of the carbon nucleophile to generate its radical species, allowing the addition with un‐activated enynes. The synthetic utility for the present protocol was demonstrated by a large‐scale reaction, as well as the derivatization of the allene product. [ABSTRACT FROM AUTHOR]

The difunctionalization of unsaturated bonds plays a vital role in the enrichment of molecular complexity. While various catalytic methods for alkene and alkyne difunctionalization have been developed in recent years, hetero‐functionalization the introduction of two different atoms has been less explored. This is mainly due to the challenges associated with achieving high chemo‐, regio‐, and stereoselectivity, especially when adding two similar atoms from the same group across unsaturated bonds. In this study, we describe a nickel‐catalyzed, three‐component reductive protocol for group 14 element hetero‐difunctionalization of 1,3‐enynes using electrochemistry. This new method is mild, selective, and general, allowing for the silyl‐, germanyl‐, and stannyl‐alkylation of enynes. Various chlorosilanes as well as chlorogermans, and chlorostannanes can be successfully used in combination with aryl/alkyl‐substituted 1,3‐enynes and primary, secondary, and tertiary alkyl bromides in the electroreductive coupling. [ABSTRACT FROM AUTHOR]

An efficient and facile one-pot protocol to access enynylboronates via a Pt-catalyzed diboration/protodeboration strategy has been developed. The reaction is suitable for various silylsubstituted symmetrical and unsymmetrical 1,3-diynes, leading to π-conjugated organoboron compounds with excellent regio- and stereoselectivity. [ABSTRACT FROM AUTHOR]

(E)-1-aryl-2,4-bis(trimethylsilyl)but-1-en-3-ynes readily undergo protodesilylation and subsequent aerobic, copper-free Sonogashira cross-coupling with aryl halides to form (E)-1,4-diaryl-2-(trimethylsilyl)but-1-en-3-ynes. The proposed one-pot, two-step approach allows access to the isomers containing aryl substituents in mutual syn positions. The resulting 2-silyl enynes can be further converted by proto- or halodesilylation. [ABSTRACT FROM AUTHOR]

In recent years, the concept of transition metal-catalyzed functionalization of unsaturated hydrocarbons has emerged as a promising strategy for developing new and valuable reactions, and has attracted considerable attention because it is efficient and atomic economical. In this critical review, we describe recent advances that have been made in the development of transition metal-catalyzed functionalization of 1,3-enynes via alkylene-π-allylpalladium intermediates. [ABSTRACT FROM AUTHOR]

A novel Lewis- and Brønsted-acid mediated electrophilic addition cyclization/amidation reaction of 1,6-enynes with nitriles to synthesize 3-enamide-substituted dihydrobenzofurans has been developed. The transformation involves the addition of a Brønsted acid as the electrophilic reagent to enynes, followed by intramolecular cyclization to form cationic intermediates, and the termination of the reaction by a nitrile as a nucleophile. The main features of the reaction include high atom economy and chemoselectivity, as well as the construction of C–C/C–N bonds in one step. [ABSTRACT FROM AUTHOR]

Alkynes as unsaturated hydrocarbons have long been used for cyclization reactions. Various transition metal-catalyzed cyclizations of alkynes have been reported in the past decades. In this minireview, we mainly summarize the recent asymmetric cyclization of alkynes with other functional groups such as carbonyl-alkynes, cyano-alkynes, and enynes under the catalytic system of nickel and chiral ligands. [ABSTRACT FROM AUTHOR]

Asymmetric sequential hydrogenations of conjugated enynes have been developed using a Ph‐BPE‐CoI catalyst for the precise synthesis of chiral Z‐allylamides in high activity (up to 1000 substrate/catalyst (S/C)) and with excellent enantioselectivity (up to >99 % enantiomeric excess (ee)). Mechanism experiments and theoretical calculations support a cationic CoI/CoIII redox catalytic cycle. The catalytic activity difference between cobalt complexes of Ph‐BPE and QuinoxP* was explained by the process decomposition of rate‐determining step in the second hydrogenation. [ABSTRACT FROM AUTHOR]

The Co2 (CO)8-mediated intramolecular Pauson–Khand reaction (PKR) is an effective method for constructing polycyclic structures. Recently, our group reported a series of this type of reaction involving fluorinated enynes that proceed with reasonable reaction rates and yields. However, mechanistic studies involving these fluorinated derivatives in intramolecular PKR are scarce. In this study, density functional theory calculations are used to clarify the mechanism and reactivity of enynes containing a vinyl fluoride moiety for this reaction. In agreement with previous studies, alkene insertion is considered to be the rate-determining step for the overall Pauson–Khand reaction of enynes containing a vinyl fluoride moiety. The effect of the substituent on the Co2 (CO)8-mediated intramolecular Pauson–Khand reaction has also been investigated. When introducing heteroatoms as tethering units, the fluorinated enynes exhibited lower reactivity than the malonate homologues, whereas the use of a sulfur-based tether was unsuccessful. This computational study provides detailed information about the PKR mechanism and transition-state structures, and the results are validated with previous experimental results. [ABSTRACT FROM AUTHOR]

Transition-metal catalyzed asymmetric cyclization of 1,6-enynes has emerged as a powerful method for the construction of carbocycles and heterocycles. However, very rare examples worked under electrochemical conditions. We report herein a Co-catalyzed enantioselective intramolecular reductive coupling of enynes via electrochemistry using H2O as hydride source. The products were obtained in good yields with high regio- and enantioselectivities. It represents the rare progress on the cobalt-catalyzed enantioselective transformation via electrochemistry with a general substrate scope. DFT studies explored the possible reaction pathways and revealed that the oxidative cyclization of enynes by LCo(I) is more favorable than oxidative addition of H2O or other pathways. 1,6 enynes are a useful synthetic building block, but their use asymmetric intramolecular reductive couplings with cobalt catalysts have not been well-explored. Here, the authors describe an enantioselective intramolecular reductive coupling of enynes via the combination of electrochemistry and cobalt catalysis. [ABSTRACT FROM AUTHOR]

We report a rhodium(I)‐catalyzed asymmetric cyclohydroformylation reaction of 1,6‐enynes with formaldehyde. The reaction of 1,6‐enynes with formaldehyde in the presence of a cationic Rh(I) catalyst, such as [Rh(cod)2]+OTf−, and a chiral biaryl diphosphine led to asymmetric cyclohydroformylation to produce aldehydes with higher‐order structures highly enantioselectively. This transformation procedure is applicable to a variety of enynes, with wide compatibility in various atoms liking between the alkyne and alkene parts, substituents at the alkyne terminus, and substituents at the alkene part, being converted to newly formed aldehydes in 14% to 90% yields with 50% to 98% ee. The products were further transformed with various nucleophiles to alcohols, an amine, and a diene without loss of chirality at their γ‐position. [ABSTRACT FROM AUTHOR]

Radical reactions are powerful in creating carbon–carbon and carbon–heteroatom bonds. Designing one-pot radical reactions with cascade transformations to assemble the cyclic skeletons with two new functional groups is both synthetically and operationally efficient. Summarized in this paper is the recent development of reactions involving radical addition and cyclization of dienes, diynes, enynes, as well as arene-bridged and arene-terminated compounds for the preparation of difunctionalization cyclic compounds. Reactions carried out with radical initiators, transition metal-catalysis, photoredox, and electrochemical conditions are included. [ABSTRACT FROM AUTHOR]

An efficient strategy for preventing the β‐hydride elimination of alkylpalladium species by ligation of the palladium with adjacent amino‐group was developed, which enabled a novel palladium‐catalyzed ring‐closing aminoalkylative amination of unactivated aminoenynes. The reaction is amenable to aminals, as well as aliphatic aldehydes with secondary amines, which provides straightforward access to structurally diverse exocyclic allenic amines bearing 5 to 12‐membered N‐heterocycles. With chiral phosphoramidite‐ligated palladium complex as the catalyst, an enantioselective variant was achieved with up to 93 % ee. Simultaneously, synthetic transformations of the chiral products were also conducted to afford structurally unique spirodiamines including one pharmaceutically active molecule via axial‐to‐central chirality transfer. [ABSTRACT FROM AUTHOR]

Aiming to study the interaction of gold with the highly Lewis acidic fluorenyl cation, we synthesised (o-[Ph2P(C6H4)Flu)AuCl(tht)][BF4] ([2][BF4]) and (o-Ph2P(C6H4)Flu)AuCl2 (3) (Flu = 9-fluorenyl) and found that the latter could be converted into [(o-Ph2P(C6H4)Flu)AuCl]+ ([4]+) upon treatment with NaBArF24 (BArF24 = B(3,5-C6H3(CF3)2)4). [4]+, which has been isolated as a chloride-bridged dimer, readily catalyses the cycloisomerisation of 2-allyl-2-(2-propynyl)malonate. Computational results show that [4]+ possesses a strong Au → C+ bond and readily activates enynes. [ABSTRACT FROM AUTHOR]

Fluoropolymers with unique structures, high chemical stability, heat resistance, hydrophobicity, and insulation to electricity, have attracted much attention, owing to their applications in low surface energy coatings, dielectric materials, solid electrolytes, ion exchange membranes, and so on. However, the synthetic approaches for fluoropolymers are quite limited, and it is crucial to develop new synthetic approaches for the pursuing of new fluoropolymer structures. Herein, a series of soluble conjugated fluoropolymers with unique 1,3‐enyne structures embedded in the polymer chain and perfluoroalkyl group as sidechains are synthesized in high yields of up to 96% from a palladium‐catalyzed polymerization of aromatic terminal diynes and perfluorobutyl iodide in 1,4‐dioxane at 80 °C using K2CO3 as the base. The chemical structures of the fluoropolymers are fully characterized by gas permeation chromatography (GPC), 1H, 13C, 19F NMR, and IR spectra, together with the comparison with the spectra of the small molecular model compound, confirming their expected polymer structures with high selectivity, high molecular weights of up to 60 500 g mol−1, good solubility, high thermal resistance, and hydrophobicity. This efficient polymerization provides a convenient tool for the preparation of fluoropolymers, promoting the development of polymer synthetic methodology and the exploration of new fluoropolymer structures and materials. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Aryl sulfonyl radical triggered cascade cyclization of phenyl‐linked 1,6‐enynes for the synthesis of biologically important indenes containing alkenyl C—X bonds and 10a,11‐dihydro‐10H‐benzo[b]fluorines is presented. In these radical cascade processes, three new chemical bonds, including C—S, C—C, and C—X bonds, and three C—C bonds are formed in one step. The method is attractive and valuable due to its metal‐free, mild reaction conditions, broad substrate scope and good functional group tolerance. [ABSTRACT FROM AUTHOR]

Visible‐light mediated hydrophosphorylation and hydrophosphorylative cyclization reactions using heterogeneous graphitic carbon nitride as the photocatalyst were described. The phosphorus atom radical was generated and allows the radical addition and addition/cyclization sequence, efficiently resulting in the final phosphorylated alkenes and cycles formation. Recyclable, nontoxic and low‐cost heterogeneous graphitic carbon nitride as visible light photocatalyst provides a new opportunity for the hydrophosphorylation and hydrophosphorylative cyclization reactions under the present redox‐neutral conditions. [ABSTRACT FROM AUTHOR]

Palladium‐catalyzed enantioselective cyclization of enynes has contributed significantly to the construction of chiral cyclic molecules. In contrast, the catalytic asymmetric cyclization involving halopalladation remains an unresolved challenge with the inevitable disturbance of the halide ions. Herein, an intramolecular chlorine transfer strategy is used to accomplish the enantioselective chloropalladation cyclization of 1,6‐enynes. This reaction provides a redox‐neutral approach to a variety of chiral α‐chloromethylene‐γ‐butyrolactones with excellent E selectivity and enantioselectivity. The precisely controlled coordination of palladium with both the in situ generated nucleophilic species and the monodentate phosphoramidite ligand is crucial for enantioselectivity. [ABSTRACT FROM AUTHOR]

Oxidation of C−B bonds is extensively used in organic synthesis, materials science, and chemically biology. However, these oxidations are usually limited to the oxidation of C(sp3)−B and C(sp2)−B bonds. The C(sp)−B bond oxidation is rarely developed. Herein we present a novel strategy for the preparation of γ‐lactones via the oxidation of enynyl boronates. This process successively involves the C(sp)−B bond oxidation, the epoxidation of C−C double bond and the lactonization. This protocol provided various γ‐lactones and unsaturated butenolides efficiently that are prevalent in numerous nature products and bioactive molecules. Most importantly, asymmetric oxidative lactonization of enynyl boronates was also achieved, providing chiral γ‐lactones in high enantioselectivities and diastereoselectivities. The versatile transformations and ubiquity of γ‐lactones shed light on the importance of this strategy in the construction and late‐stage functionalization of complex molecules. [ABSTRACT FROM AUTHOR]

Disclosed here is the first geminal (gem‐) hydroborative cyclization of enynes. Different from known hydroborative cyclizations, this process adds hydrogen and boron to the same position, leading to a new reaction mode. With [Cp*RuCl]4 as catalyst, a range of gem‐hydroborated bicyclic products bearing a cyclopropane unit could be rapidly assembled from simple enyne substrates. Control experiments and density functional theory (DFT) calculations provided important insights into the reaction mechanism. Notably, two major competing pathways may operate with substrate‐dependence. 1,6‐Enynes favor initial oxidative cyclometalation to form a ruthenacyclopentene intermediate prior to engaging hydroborane, while other enynes (e.g. 1,7‐enynes) that lack strong propensity toward cyclization prefer initial alkyne gem‐(H,B)‐addition to form an α‐boryl ruthenium carbene followed by intramolecular olefin cyclopropanation. This process also represents the first ruthenium‐catalyzed enyne hydroborative cyclization. [ABSTRACT FROM AUTHOR]

Metal‐free borylative cyclization of biphenyl‐embedded 1,3,5‐trien‐7‐ynes in the presence of simple and inexpensive BCl3 provided synthetically useful borylated building blocks. The outcome of the process depends on the reaction temperature, with borylated phenanthrenes obtained at 60 °C and phenanthrene‐fused borylated cyclobutanes formed at 0 °C. Based on DFT calculations, a mechanism for these novel transformations has been proposed, which involves an uncommon skeletal rearrangement, including migration of a methyl group and alkyne fragmentation, unprecedented in BCl3‐promoted cyclization reactions. [ABSTRACT FROM AUTHOR]

With increasing demand for customized commodities and the greater insight and understanding of olfaction, the synthesis of fragrances with diverse structures and odor characters has become a core task. Recent progress in organic synthesis and catalysis enables the rapid construction of carbocycles and heterocycles from readily available unsaturated molecular building blocks, with increased selectivity, atom economy, sustainability and product diversity. In this review, synthetic methods for creating cyclic fragrances, including both natural and synthetic ones, will be discussed, with a focus on the key transformations of alkenes, alkynes, dienes and enynes. Several strategies will be discussed, including cycloaddition, catalytic cyclization, ring-closing metathesis, intramolecular addition, and rearrangement reactions. Representative examples and the featured olfactory investigations will be highlighted, along with some perspectives on future developments in this area. [ABSTRACT FROM AUTHOR]

Asymmetric construction of C(sp3)–C(sp3) bond with good stereocontrol of the two connecting carbon centres retaining all carbon or hydrogen substituents is a challenging target in transition metal catalysis. Transition metal-catalysed reductive coupling of unsaturated π-substrates is considered as a potent tool to expediently develop the molecular complexity with high atom efficiency. However, such an asymmetric and intermolecular process has yet to be developed fully. Herein, we report an efficient strategy to reductively couple two prochiral conjugate alkenes using a copper-catalysed tandem protocol in the presence of diboron. Notably, this transformation incorporates a wide range of terminal and internal enynes as coupling partners and facilitates highly diastereo- and enantioselective synthesis of organoboron derivatives with multiple adjacent stereocentres in a single operation. Asymmetric construction of alkyl C–C bonds with good stereocontrol of the two connecting carbons, particularly when using alkenes as feedstocks, is challenging. Here, the authors show a catalytic method to form multiple adjacent carbon stereocentres in a single operation. [ABSTRACT FROM AUTHOR]

A simple, regioselective and high yielding gold‐catalyzed synthesis of benzofulvenes, from progargylsilanes and benzophenones, is described. Initially, the carbonyl compound is synergistically activated by the silyl moiety and, for the cyclization step, the gold catalytic activity is clearly increased by the participation of aluminum trichloride, acting as a cocatalyst. Several mechanistic intermediates, such as enynes and silylbenzofulvenes, have been isolated. Different control experiments have been performed, indicating the participation of [LAu][NTf2AlCl3] complex as the true catalyst, and revealing a dramatic enhancement of the gold activity by coordination of the Lewis acid to the gold counterion. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations have been performed to gain insight into the reaction mechanism of the Co(I)‐catalyzed asymmetric [2 + 2] cycloaddition reaction of enyne 1a with ethylene 2 to give the functionalized cyclobutene E‐4a possessing a chiral, all‐carbon quaternary center in the ring framework (Science, 361, 68–72). This study reveals that the whole catalysis can be characterized via three stages: (i) oxidative dimerization followed by reductive elimination gives the intermediate IM3, (ii) the alkenyl‐Co(III) metallacycloheptene IM6 formation with the addition of another equivalent ethylene via an oxidative dimerization process, (iii) β‐Hydrogen elimination and reductive elimination from IM6 to result in the final product E‐4a and regenerate the active speices IM1 for the next catalytic cycle. Each stage is kinetically and thermodynamically feasible for experimental realization under mild conditions, and the formation of the alkenyl‐Co(III) metallacycloheptene IM6, with a barrier of 27.2 kcal mol−1 (i.e., IM2 → TS4), should be the rate‐determining step (RDS) during the whole catalysis. In addition, the origins of enantioselectivity and regioselectivity of the product are discussed. [ABSTRACT FROM AUTHOR]

A general palladium‐catalyzed method for the direct alkynylation of unactivated alkenes via C−H activation, was successfully developed, with the assistance of 8‐aminoquinoline. It is applicable to both internal and terminal unactivated alkenes with a broad functionality tolerance. This method shows good regio‐ and diastereoselectivity and provides an alternative approach for directing construct of conjugated 1,3‐enynes. [ABSTRACT FROM AUTHOR]

An efficient protocol for the synthesis of 3‐ethynyl‐2‐aryl‐bicyclo[3.1.0]hexenes through a gold‐catalyzed enyne cyclization was established in this work. Depending on the specific substitution pattern, unusual cationic rearrangements of the corresponding gold carbene were revealed, leading to either cyclohexadienes or 5,9‐methanobenzo[8]annulene derivatives, respectively. [ABSTRACT FROM AUTHOR]

A novel and efficient radical-modulated difunctionalization of vinyl enynes has been disclosed using TEMPO as a radical regulator. Facile access to structurally diverse 3-bromo-naphthalen-1(2H)-ones and 4-bromo-allenic alcohols was realized via 1,2-addition/1,2-migration or 1,4-addition, respectively. This protocol represents the first example of radical-modulated metal-free difunctionalization of 1,3-enynes with high regioselectivity. [ABSTRACT FROM AUTHOR]

This review highlights the hydroelementation reactions of conjugated and separated diynes, which depending on the process conditions, catalytic system, as well as the type of reagents, leads to the formation of various products: enynes, dienes, allenes, polymers, or cyclic compounds. The presence of two triple bonds in the diyne structure makes these compounds important reagents but selective product formation is often difficult owing to problems associated with maintaining appropriate reaction regio- and stereoselectivity. Herein we review this topic to gain knowledge on the reactivity of diynes and to systematise the range of information relating to their use in hydroelementation reactions. The review is divided according to the addition of the E–H (E = Mg, B, Al, Si, Ge, Sn, N, P, O, S, Se, Te) bond to the triple bond(s) in the diyne, as well as to the type of the reagent used, and the product formed. Not only are the hydroelementation reactions comprehensively discussed, but the synthetic potential of the obtained products is also presented. The majority of published research is included within this review, illustrating the potential as well as limitations of these processes, with the intent to showcase the power of these transformations and the obtained products in synthesis and materials chemistry. [ABSTRACT FROM AUTHOR]

Metal-catalyzed [2+2+2] cycloaddition is a powerful tool that allows rapid construction of functionalized 6-membered carbo- and heterocycles in a single step through an atom-economical process with high functional group tolerance. The reaction is usually regio- and chemoselective although selectivity issues can still be challenging for intermolecular reactions involving the cross-[2+2+2] cycloaddition of two or three different alkynes and various strategies have been developed to attain high selectivities. Furthermore, enantioselective [2+2+2] cycloaddition is an efficient means to create central, axial, and planar chirality and a variety of chiral organometallic complexes can be used for asymmetric transition-metal-catalyzed inter- and intramolecular reactions. This review summarizes the recent advances in the field of [2+2+2] cycloaddition. 1 Introduction 2 Formation of Carbocycles 2.1 Intermolecular Reactions 2.1.1 Cyclotrimerization of Alkynes 2.1.2 [2+2+2] Cycloaddition of Two Different Alkynes 2.1.3 [2+2+2] Cycloaddition of Alkynes/Alkenes with Alkenes/Enamides 2.2 Partially Intramolecular [2+2+2] Cycloaddition Reactions 2.2.1 Rhodium-Catalyzed [2+2+2] Cycloaddition 2.2.2 Molybdenum-Catalyzed [2+2+2] Cycloaddition 2.2.3 Cobalt-Catalyzed [2+2+2] Cycloaddition 2.2.4 Ruthenium-Catalyzed [2+2+2] Cycloaddition 2.2.5 Other Metal-Catalyzed [2+2+2] Cycloaddition 2.3 Totally Intramolecular [2+2+2] Cycloaddition Reactions 3 Formation of Heterocycles 3.1 Cycloaddition of Alkynes with Nitriles 3.2 Cycloaddition of 1,6-Diynes with Cyanamides 3.3 Cycloaddition of 1,6-Diynes with Selenocyanates 3.4 Cycloaddition of Imines with Allenes or Alkenes 3.5 Cycloaddition of (Thio)Cyanates and Isocyanates 3.6 Cycloaddition of 1,3,5-Triazines with Allenes 3.7 Cycloaddition of Aldehydes with Enynes or Allenes/Alkenes 3.8 Totally Intramolecular [2+2+2] Cycloaddition Reactions 4 Conclusion [ABSTRACT FROM AUTHOR]