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An Rh(III)-catalyzed C-H activation of pyrazolones with 1,6-enynes was investigated. The regioselectivity of the C-H activation/alkyne insertion is readily solved by using symmetric enyne coupling partners, and a C-H activation-triggered cascade reaction is realized, which involves alkyne insertion, tautomerization, and double cyclization to offer a class of structurally complex polycyclic architectures. This cascade reaction tolerates a broad substrate scope in high regioselectivity and stereospecificity and furnishes three new chemical bonds and four chiral centers in a single operation. Various derivatizations of the polycyclic scaffolds are conducted, providing products with ample space for further functional transformations. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed hydroxycyclization reaction of 1,7-enynes to afford seven-membered silacycles (1H-benzo[b]silepine skeletons) is developed. This is the first example of both seven-membered ring construction from enynes using a palladium catalyst and hydroxycyclization of enynes to give seven-membered silacycles. [ABSTRACT FROM AUTHOR]

A novel procedure for the synthesis of cyclohexanones from alkynol or enyne derivatives through a cationic cyclization has been developed. The key points to obtain the six-membered ring derivatives are the use of starting materials containing a terminal alkyne, the use of tetrafluoroboric acid as a promoter of the cationic cyclization, and the appropriate selection of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as solvent. This strategy can be extended to the biomimetic cationic cyclization of several terpene-derived polyenynes. [ABSTRACT FROM AUTHOR]

A mild, efficient, and novel rhodium catalyzed asymmetric cyclization-addition domino reaction of oxa/azabenzonorbornadienes and 1,6-enynes is documented. Through the use of a [Rh(COD)2]BF4-(R)-An-SDP catalytic system, highly enantioenriched cyclization-addition products were obtained in good yields and with excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

A regioselective 2,4-dibromohydration of conjugated enynes is reported for the synthesis of 2-(2,4-dibromobut-2-enoyl)benzoate. In the presence of tetra-n-butylammonium bromide and H2O the transformation proceeds smoothly with good reaction efficiency and a broad reaction scope. Mechanism studies indicate that the neighboring ester group participates in the 2,4-dibromohydration, and the oxygen atom of ester is transferred into the C–C triple bond to form the keto carbonyl group in the product. 2-(2,4-Dibromobut-2-enoyl)benzoate is recognized as an important synthon toward phthalazin-1(2H)-one and the natural product Shihunine. [ABSTRACT FROM AUTHOR]

Cascade radical cyclization of 1,6-enynes for the synthesis of biologically important γ-lactams containing alkenyl C-X bonds is reported. In these radical cascade processes, three new chemical bonds, including C-S, C-C, and C-X bonds, are formed in one step. The method is attractive and valuable due to its mild reaction conditions, broad substrate scope, and the importance of the corresponding γ-lactam products. [ABSTRACT FROM AUTHOR]

Sulfonated tetrahydropyridine derivatives are accessed through a radical reaction of 1,6-enynes, sulfur dioxide, and aryldiazonium tetrafluoroborates under mild conditions. Sulfonated pyrrolidine can be generated when terminal alkyne is used as the substrate. This reaction proceeds efficiently in dichloroethane without the addition of any catalysts or additives, providing sulfonated tetrahydropyridine derivatives in moderate to good yields. During this transformation, aryldiazonium tetrafluoroborates cooperate with DABCO•(SO2)2 leading to sulfonyl radicals, which initiate the radical cyclization process. Two molecules of aryldiazonium tetrafluoroborates are involved in the reaction. [ABSTRACT FROM AUTHOR]

An efficient gold-catalyzed ring-expansion reaction of enyne-lactones to form 2-oxoninonium intermediates is reported. The 2-oxoninonium generated in this work could undergo further 6p electrocyclization and aromatization reaction to produce different aromatic compounds. [ABSTRACT FROM AUTHOR]

A novel method for the synthesis of trifluoromethyl-containing 1'H-spiro[azirine-2,4'-quinolin]-2'(3'H)-ones by a CF3-radical-triggered tandem reaction of benzene-linked 1,7-enynes is described. This protocol utilizes 1-trifluoromethyl-1,2-benziodoxole as the trifluoromethylating reagent and TMSN3 as the aminating reagent. By this method, various potentially bioactive trifluoromethylated 1'H-spiro[azirine-2,4'-quinolin]-2'(3'H)-ones were facilely synthesized via a radical cascade process. [ABSTRACT FROM AUTHOR]

An unprecedented palladium-catalyzed allylic alkylation of pronucleophiles with unactivated skipped enynes has been developed. This method provides a straightforward access to a wide array of 1,3-dienes without the need to preinstall leaving groups or employ extra oxidants. The reaction exhibited high atom economy, good functional group tolerance, excellent regioselectivities, and scalability. With D2O as cosolvent, deuterium could be incorporated in high efficiency. [ABSTRACT FROM AUTHOR]

It has been established that a cationic rhodium(I)/(R)-MeO-BIPHEP complex catalyzes the asymmetric [2 + 2 + 2] cyclization of 1,6-enynes with aliphatic and aromatic alkenes to produce chiral cyclic dienes through β-hydride elimination from rhodacycle intermediates. Thus, obtained chiral cyclic dienes could be converted to chiral spirocompounds without racemization. [ABSTRACT FROM AUTHOR]

A convenient protocol for the synthesis of sulfonylated benzofurans via Ag-catalyzed oxidative cyclization has been established. Chemically stable and easily available sodium sulfinates were used as the sulfonylation reagents and building block for the heterocycle construction. With this novel strategy, various benzofurans bearing dual functional groups could be obtained in good yields with high chemo- and regioselectivities under mild conditions. [ABSTRACT FROM AUTHOR]

An Fe(OTf)3-catalyzed 1,5-enyne cycloisomerization via 5-endo-dig cyclization is described for the synthesis of 3-(1-indenyl)indole derivatives. Since a variety of 1,5-enynes are readily accessible via Heck-Suzuki coupling, this strategy provides a rapid and easy access to a wide range of highly substituted 3-(1-indenyl)indoles in good yields. [ABSTRACT FROM AUTHOR]

Cascade radical cyclization of 1,6-enynes for the construction of biologically important polycyclic γ-lactams and related heterocycles is reported. In these radical cascade processes, three new C-C bonds are formed and transition metals are not required to run these sequences. The mild reaction conditions, broad substrate scope, and the importance of the heterocyclic products render the approach valuable. [ABSTRACT FROM AUTHOR]

A tandem catalytic strategy enabling one-pot, three-component couplings of electron-rich phenols, 2-nitro 1,3-enynes, and vinyl ketones was achieved. This chemistry combined mechanistically distinct [3 + 3]-annulation and nitro-Michael addition using a single squaramide catalyst, leading to the construction of novel chiral quaternary 3-nitrochromane architecture with high chemo-, regio-, and stereoselectivity. [ABSTRACT FROM AUTHOR]

The ruthenium-catalyzed 1,6-enyne cyclization in the presence of bulky substituted terminal alkyne proceeds smoothly at room temperature to afford highly substituted five-membered cyclic compounds featuring a 1,5-enyne motif. Deuterium-labeling experiments showed that the key ruthenacyclopentene intermediate undergoes cleavage of metal-carbon bonds through the metal-assisted σ-bond metathesis reaction, thus leading to the formation of C(sp²)-H and C(sp³)-C(sp) bonds. [ABSTRACT FROM AUTHOR]

An organocatalytic asymmetric formal [3 + 2] cycloaddition of enynones with N-hydroxylamines has been described. A newly designed multifunctional organocatalyst was found to be highly effective, and the method allowed the synthesis of a variety of 2,3-dihydroisoxazoles in good yields with excellent enantioselectivity. [ABSTRACT FROM AUTHOR]

An iron-catalyzed radical [2 + 2 + 2] annulation of benzene-linked 1,7-enynes with aldehydes has been developed. With this method, a variety of fused [6.6.6] pyran molecules are built in an efficient and selective manner. The aldehydic radical-mediated strategy exhibits a particularly attractive dual role, which triggers and terminates the domino cyclization. [ABSTRACT FROM AUTHOR]

A novel strategy to synthesize 1,3-enynes has been successfully developed based on Cu(I)-catalyzed cross-coupling of α-diazo phosphonates and alkynes with a subsequent Horner-Wadsworth-Emmons (HWE) type reaction. This method provides straightforward access to conjugated enynes with high efficiency, good stereoselectivity and excellent functional group compatibility. Copper(I) carbene migratory insertion plays a crucial role in this transformation. [ABSTRACT FROM AUTHOR]

The poor regioselectivity of the [4 + 2] cycloaddition of 3-azetidinones with internal alkynes bearing two alkyl substituents via nickel-catalyzed carbon-carbon activation is addressed using 1,3-enynes as substrates. The judicious choice of substitution on the enyne enables complementary access to each regioisomer of 3-hydroxy-4,5-alkyl-substituted pyridines, which are important building blocks in medicinal chemistry endeavors. [ABSTRACT FROM AUTHOR]

Synergistic rhodium/copper catalysis enables new three-component coupling reactions of terminal alkynes and α-diazoketones and/or arylamines, allowing dediazotized carbene C-H insertion for the synthesis of functionalized 1,3-enynes and N-aryl enaminones with high stereoselectivity. The synthetic utility of these transformations results in subsequent C-C or/and C-N bond-forming reactions to effectively build up functional molecules with potential significance. [ABSTRACT FROM AUTHOR]

It has been established that a cationic rhodium(I)/H8-BINAP complex catalyzes the asymmetric [2 + 2 + 2] cycloaddition of 1,6-enynes with cyclopropylideneacetamides to produce spirocyclohexenes in excellent enantioselectivity with retaining cyclopropane rings. [ABSTRACT FROM AUTHOR]

A new strategy toaccess macrocyclic enynes was developed. To blockundesired ene–yne cyclization pathways, alkynes were protectedvia bromination and the resultant acyclic vic-(E)-dibromotrienes participated in selective ene–enering closing metathesis reactions. Zinc-promoted deprotection of (E)-dibromodienes provided macrocyclic enynes in high yields. [ABSTRACT FROM AUTHOR]

Intramolecular[4 + 4] photoreaction of 2-pyrones with a 1,3-enyneyields an unstable 1,2,5-cyclooctatriene product. Without a C4 pyronesubstituent, 1,3-hydrogen migration converts the allene to a 1,3-diene,with a skeleton related to dactylol. With methoxy substitution, Coperearrangement yields a nine-membered ring fused to a cyclobutane.Both structures were confirmed by X-ray crystallography. The Coperearrangement is apparently reversible, reforming the allene whichundergoes a proton shift to the more stable 1,3-diene product. [ABSTRACT FROM AUTHOR]

A base-catalyzed selective cycloisomerization of 3-aza-1,5-enynes is developed. This transformation provides a facile access to highly functionalized 2-azabicyclo[3.2.0]hept-2-enes and sulfonyl vinyl-substituted pyrroles. The chemoselectivity was controlled by the substituent pattern of the substrates. [ABSTRACT FROM AUTHOR]

A AgSCF3-mediated radical cascade cyclization/trifluoromethylthiolationof 1,6-enynes triggered by a C–C triple bond is developed.This protocol also provides another opportunity to construct a valuabletrifluoromethylthio-substituted polycyclic fluorene system throughthe formations of one C–SCF3bond and two C–Cbonds in a single step. [ABSTRACT FROM AUTHOR]

C-C Bond formation and β-F elimination have been achieved in a Cu(I)-catalyzed cross-coupling reaction of terminal alkynes and trifluoromethyl ketone N-tosylhydrazones. The reaction represents an efficient synthesis of 1,1-difluoro-1,3-enyne derivatives. Mechanistically, the migratory insertion of the copper carbene intermediate leads to the C-C bond formation, which is followed by C-F bond cleavage. [ABSTRACT FROM AUTHOR]

The development of a sequential O-H/C-H bond functionalization of phenols initiated by the cationic gold(I)-catalyzed cyclization of 1-bromo-1,5-enynes to produce (2-bromocyclopent-2-en-1-yl)phenols is reported. This unprecedented domino transformation efficiently proceeds under mild conditions (5 mol % of (t-Bu)3PAuNTf2, CH2Cl2, 0-23 °C) via an intermediate aryl alkyl ether which collapses at ambient temperature to undergo a 1,2-hydride shift followed by C-H insertion of the phenol. [ABSTRACT FROM AUTHOR]

A novel copper-catalyzed cascadecyclization of 1,7-enynes withmetal sulfides is described. This sulfur-incorporation method providesstraightforward access toward the important thiophene-fused quinolin-4(5H)-one scaffold through cyclization and double C–Sbond formation cascade, and the chemoselectivity of this 1,7-enynecyclization toward 1,3,3a,9b-tetrahydrothieno[3,4-c]quinolin-4(5H)-ones and 3,3a-dihydrothieno[3,4-c]quinolin-4(5H)-ones can be controlledby varying the sulfur resources. [ABSTRACT FROM AUTHOR]

We report here anenantioselective formal synthesis of vinigrolinvolving a 1–2–3 strategy: one pot and two reactionswith the formation of three rings leading to the core structure ofvinigrol from its stereochemically well-defined acyclic precursor. [ABSTRACT FROM AUTHOR]

The cycloisomerizationof vinyl silicon-tethered 1,7-enynes hasbeen accomplished using catalytic Cp*Ru(COD)Cl. The products possessa new silane moiety and trisubstituted alkenes as part of the dienesystem. The reaction scope includes aryl, alkyl, vinyl, and cyclopropylalkyne functionalities. Silicon was found not to be a mandatory componentof the tether. The utility of the products was demonstrated throughmanipulation of the vinyl silane and Diels–Alder chemistry. [ABSTRACT FROM AUTHOR]

Regiocontrolled synthesis of polysubstitutedbenzenes from silylated1,3-dien-5-ynes has been achieved by using diisobutylaluminum hydride(DIBAL-H). Hydroalumination of the alkyne moiety with DIBAL-H triggersthe aromatic cyclization, which usually proceeds without rearrangementand loss of the existing substituents. The related unusual cyclizationsto different types of polysubstituted benzenes are also described. [ABSTRACT FROM AUTHOR]

A highlychemo- and stereoselective cobalt-catalyzed hydroarylativecyclization of 1,6-enynes with aromatic ketones and esters to synthesizefunctionalized pyrrolidines and dihydrofurans is described. A mechanisminvolving cobaltacycle triggered C–H activation of aromaticketones and esters was proposed. [ABSTRACT FROM AUTHOR]

Reactive1,2,5-cyclooctatrienes, formed by photocycloaddition of2-pyridones with enynes, are stabilized by steric shielding, slowingor preventing an otherwise facile [2 + 2]-dimerization reaction. Diisopropylsilylether-tethered reactants paired with an alkene substituent (R) produceallenes that are stable (R = TMS) or that isomerize to 1,3-dienesby hydrogen migration (R = alkyl). Under acidic conditions, hydrolysisof the photoproduct’s silyl ether can lead to a [3,3]-sigmatropicrearrangement. [ABSTRACT FROM AUTHOR]

A novel three-componentstrategy for the cyanotrifluoromethylation/azidotrifluoromethylationand carbocyclization of 1,6-enynes is developed. The reaction proceedssmoothly under a moderate temperature by using a copper catalyst,which provides a rapid and concise access to addition–carbocyclizationproducts. Furthermore, the products obtained can be useful buildingblocks in discoveries of lead compounds and other biologically activeCF3-containing heterocycles. [ABSTRACT FROM AUTHOR]

An I2O5-promotedfree-radical cascade trifluoromethylation/cyclizationof a broad range of N-arylmethacrylamides and enyneswith sodium trifluoromethanesulfinate in aqueous medium has been achieved.This strategy allows highly selective access to a variety of CF3-containing oxindoles and pyrrolidines. Electron spin resonance(ESR) studies indicate that atom-transfer processes are involved inthis system. [ABSTRACT FROM AUTHOR]

Enynes are versatilebuilding blocks in organic synthesis. A copper-catalyzedHiyama-type cross-coupling of vinylsiloxanes with bromoalkynes ispresented. This mild and efficient method led to the formation ofvarious sensitive enynes. The use of cis, trans, and 1,1′-disubstituted vinylsiloxanes wasallowed, and full retention of stereochemistry was observed. Sensitivegroups such as halides, unsaturated ketones, and aldehydes were fullytolerated. [ABSTRACT FROM AUTHOR]

Thecatalytic enantioselective conjugate addition of acetaldehydeto polyconjugated substrates, nitrodienynes and nitroenynes, has beenaccomplished using organocatalysis. Various functionalized 1,3-enynesand propargylic compounds were obtained in moderate to good yieldswith high enantioselectivity. The synthetic utilities of the conjugateaddition reactions have been highlighted in the concise total synthesisof (+)-α-lycorane and the metal-free synthesis of chiral β-alkynylacids. [ABSTRACT FROM AUTHOR]

A phosphine-mediated regio- and stereoselectiveaddition reactionof diverse nucleophiles to yne-enones leading to polysubstituted 1,3-dienescaffolds in moderate to good yields has been reported. [ABSTRACT FROM AUTHOR]

Despite the possibility of intermolecular attack at four different locations, the Bu3Sn-mediated radical cyclization of aromatic enynes is surprisingly selective. The observed reaction path originates from the leaststable of the equilibrating pool of isomeric radicals produced by intermolecular Bu3Sn attack at the π-bonds of substrates. The radical pool components are kinetically self-sorted via 5-exo-trig closure, the fastest of the four possible cyclizations. The resulting Sn-substituted indenes are capable of further transformations in reactions with electrophiles. [ABSTRACT FROM AUTHOR]

A facile synthetic route to access polyfluoroalkyl functionalized cyclobutenes bearing an exo cyclic double bond from 3-aza-1,5-enynes is reported. The reaction proceeds via a thermal aza-Claisen rearrangement to give an allene-imine intermediate; subsequent cyclization affords the cyclobutene core. The kinetics of the transformation of starting material and the intermediate was studied by 1H NMR spectroscopy, where a consecutive reaction was revealed. [ABSTRACT FROM AUTHOR]

An atom-economic route to thiophenes and bithiophenes has been developed starting from the readily available gem-dialkylthio enynes. A range of functionalized thiophenes and bithiophenes, bearing a pendent vinylthio group, were obtained in good to high yields under mild conditions. [ABSTRACT FROM AUTHOR]

A tandem process provides high-value 1,6-enynes that are otherwise difficult to prepare. Two base-mediated reactionsfragmentation and olefinationare executed in a coordinated manner that is overall more efficient than either reaction on its own. The 1,6-enynes can be strategically employed in conjunction with carbocyclization to deliver important targets, as noted for reported syntheses of hirsutene and illudol. [ABSTRACT FROM AUTHOR]

An effective reflexive-Michael (r-M) reaction has been disclosed to access drug-like six-membered spirooxindoles in good yields and excellent enantioselectivities by using an aminoenyne-catalysis. [ABSTRACT FROM AUTHOR]

A rhodium and Brønsted acid catalyzed one-pot cycloisomerization/hetero-Diels–Alder reaction of 1,6-enynes with unactivated aldehydes was established under mild conditions. This one-pot catalytic protocol produced a wide variety of annulated dihydropyrans from readily available starting materials in a highly atom economical manner. [ABSTRACT FROM AUTHOR]

The gold(I)-catalyzed [2 + 2] cycloaddition of large 1,n-enynes (n= 10–16) provides access to 9- to 15-membered ring macrocycles incorporating a cyclobutene moiety. The reaction requires the use of a gold(I) catalyst bearing a sterically hindered biphenylphosphine ligand. [ABSTRACT FROM AUTHOR]

In the presence of Pd(0) and a phosphine, hydrosilylation of 1,3-enynes with Me2SiHCl proceeds to yield dienylsilanes with the silicon function added to the internal alkyne carbon atom and with (E)-configuration of newly formed olefinic bond. The silanols isolated after hydrolysis of the primarily obtained products serve as precursors to conjugated dienes with different substitution patterns. [ABSTRACT FROM AUTHOR]

An efficient synthetic method of functionalized naphthalenes having hydrogen, alkyl, alkenyl, aryl, or heteroaryl groups on the 4-position and ethoxycarbonyl group on the 2-position was developed through selective Pt-catalyzed 6-endointramolecular hydroarylation of ethyl (E)-2-ethynyl/alkynyl cinnamates. [ABSTRACT FROM AUTHOR]

This work demonstrates a green and efficient method to prepare 1,3-enynes via Pd(II)-catalyzed direct dehydrogenative olefination of terminal arylalkynes with unactived allylic ethers. Various terminal arylalkynes can participate in the reaction, stereoselectively affording the desired conjugated (Z)-1,3-enynes in moderate to good yields. [ABSTRACT FROM AUTHOR]

The first cross-reaction between a terminal silylacetylene and two ketene molecules leading to 1,3-enynes bearing a carboxylic ester group via double insertion of ketenes is achieved using a cationic rhodium complex catalyst. This reaction is applicable for various symmetrical and unsymmetrical ketenes with good stereoselectivities. [ABSTRACT FROM AUTHOR]