One‐Shot Double Elimination Process: A Practical and Concise Protocol for Diaryl Acetylenes

A variety of diaryl acetylenes were obtained in good yields when lithium hexamethyldisilazide was added to a solution of arylmethyl sulfone, aryl aldehyde, and chlorodiethylphosphate in THF. In this one‐shot process, a number of transformations such as aldol reaction, phosphorylation of aldolate, and double elimination of the resulting β‐substituted sulfone proceeded successively to afford the desired acetylenes. The one‐shot process was accelerated by the substitution of halogen atoms on the phenyl groups, and unsymmetrically substituted diaryl acetylenes were obtained without contamination of the dehalogenated products. Diaryl acetylenes with other substituents such as CF₃, ethoxycarbonyl, dimethylamino, TMS‐acetylene groups, as well as pyridinyl and thienyl moieties were also accessible with this method. However, methoxy‐substituted compounds were obtained in moderate yields under the same conditions, but the yields were increased when lithium diisopropylamide was used instead.     

A highly regio- and stereo-selective hydrostannation reaction of various fluorine-containing internal acetylene derivatives

The hydrostannation reaction of various fluoroalkylated acetylene derivatives with tributyltin hydride was investigated using a variety of catalysts in toluene. Among them, the Et₃B-induced hydrostannation reaction gave the highest regio- and stereo-selectivity. Their selectivity was mostly influenced upon the difference of the substituent X at the aromatic ring of the aryl-substituted internal acetylenes. Thus, the acetylenes having a halogen atom or an electron-donating group as X reacted smoothly with tributyltin hydride, affording the vinylstannane 4Z exclusively, while the acetylenes having an electron-withdrawing group (X=CO₂Et, NO₂) resulted in the preferential formation of 5E. The plausible mechanism of the formation of these products was discussed.     

Synthesis and properties of polyfluoro(silyl)acetylene nanoparticles by reaction of fluoro(silyl)acetylenes with triethylamine

Fluoro(silyl)acetylenes, which were prepared by reaction of 1,1-difluoroethylene with silyl chlorides, reacted with triethylamine to give dark-brown colored polyfluoro(silyl)acetylene powders in excellent to moderate isolated yields. In contrast, the corresponding nonfluorinated acetylene was unable to react with triethylamine at all to afford poly(silyl)acetylene under similar conditions. Polyfluoro(silyl)acetylenes thus obtained were nanometer size-controlled cubic fine particles with a good dispersibility and stability in a variety of solvents. These polyfluoro(silyl)acetylene nanoparticles exhibited clear absorption and emission spectra related to the conjugated units in polymer main chain. Furthermore, these polyfluoro(silyl)acetylene nanoparticles were applied to the surface modification of poly(methyl methacrylate) [PMMA] film to exhibit a higher oleophobicity imparted by fluorine on their surface, compared to that on the reverse side.

New reactions of alkynes with ketones in superbasic media

The present work reviews new reactions of alkynes with ketones in the superbasic media MOH—DMSO (M = Na, K, Cs) and KOBu^t—DMSO: the stereoselective nucleophilic addition of deprotonated ketones to the triple bond to form the E-isomers of β,γ-enones; vinylation of tertiary acetylenic alcohols that formed in situ from acetylene and ketones; the direct synthesis of vinyl ethers of tertiary acetylenic alcohols from acetylene and ketones; the stereoselective synthesis of dispirocyclic ketals containing the Z-ethylene fragment from arylalkynes and two molecules of a cyclic ketone; the stereoselective cascade synthesis of hexahydroazulenones from two arylalkyne molecules and 2-alkylcyclohexanones; the stereoselective cascade assembly of 7-methylidene-6,8-dioxabicyclo[3.2.1]octanes from two acetylene molecules and two ketone molecules; the stereoselective cascade synthesis of 7-methylidene-6,8-dioxabicyclo[3.2.1]octanes from acetylenes and 1,5-diketones; and the three-component cascade reaction of acetylene, ketones, and oximes to afford 4-methylidene-3-oxa-1-azabicyclo-[3.1.0]hexanes.     

Alkynyl- and Alkenyl(phenyl)iodonium Compounds. New Synthetic Methods (86)

Compounds with highly coordinated, polyvalent main-group elements represent an interesting alternative to the many well-known transition-metal complexes. Among the oldest and best known stable examples of such organic molecules are the iodine(III) compounds. Diaryliodonium species, Ar₂IX, for example, have been known for over a hundred years and play an important role in lithography. Likewise, acetylenes and olefins are among the oldest, most important, and most valuable compounds in chemistry. Besides simple hydrocarbon alkenes and alkynes, numerous functionalized derivatives are also known and widely employed in organic chemistry. Despite the ubiquity and prominance of both I^III species and olefins and acetylenes, the combination of these two types of functional groups in a single molecular unit, namely compounds with polyvalent iodine and at least one alkyne or olefin residue, was unknown until recently. The successful preparations of simple alkynyl- and alkenyl-(phenyl)iodonium species during the 1980s has resulted in a renaissance in both acetylene and I^III chemistry. These alkynyliodonium compounds readily undergo nucleophilic substitution on the alkyne moiety (S_N-A reactions) which are difficult with other substrates. The application of a wide variety of nucleophiles in this reaction resulted in diverse functionalized alkynes including previously unknown acetylenic carboxylates, sulfonates, and phosphates. These are excellent substrates for cycloaddition reactions as well as numerous other interesting chemical transformations.     

A convenient and efficient ring-opening reaction of aziridines with acetylenes and synthesis of dihydropyrroles

In the presence of ^tBuOK, reaction of acetylenes with N-Ts substituted aziridines derived from both cyclic and acyclic alkenes at room temperature gave rise to homopropargylamines in good to high yields and in high regioselectivity. Not only Ph- and Me₃Si-substituted acetylenes but also acetylene itself was suitable reagents. Treatment of ring-opening products with I₂ and AgOAc in the presence of K₂CO₃ provided dihydropyrroles in high yields. One-pot synthesis of dihydropyrroles was also realized by the reaction of aziridines and phenylacetylene in the presence of NaH followed by the treatment with I₂ and AgOAc.     

One-pot synthesis of metalated pyridines from two acetylenes, a nitrile, and a titanium(II) alkoxide

Four-component coupling process involving two acetylenes, a nitrile, and a divalent titanium alkoxide reagent, Ti(O-i-Pr)(4)/2i-PrMgCl, directly yielded titanated pyridines in a highly selective manner. The reaction can be classified into four categories: (i) a combination of an internal acetylene, a terminal acetylene, sulfonylnitrile, and the titanium reagent to yield alpha-titanated pyridines, (ii) a combination of an internal acetylene, a (sulfonylamino)acetylene, a nitrile, and the titanium reagent to yield alternative alpha-titanated pyridines, (iii) a combination of an internal acetylene, a (sulfonylamino)acetylene, a nitrile, and the titanium reagent to yield titanated aminopyridines, and (iv) a combination of an acetylenic amide, a terminal acetylene, a nitrile, and the titanium reagent to yield pyridineamides with their side chain titanated. Some of these reactions enabled virtually completely regioselective coupling of two different, unsymmetrical acetylenes and a nitrile to form a single pyridine. Synthetic applications of these reactions have been illustrated in the preparation of optically active pyridines and medicinally useful compounds.     

Triplet acetylenes as synthetic equivalents of 1,2-bicarbenes: phantom n,pi state controls reactivity in triplet photocycloaddition

Diaryl acetylenes, in which one of the aryl groups is either a pyridine or a pyrazine, undergo efficient triplet state photocycloaddition to 1,4-cyclohexadiene with formation of 1,5-diaryl substituted tetracyclo[3.3.0.0(2,8).0(4,6)]octanes (homoquadricyclanes). In the case of pyrazinyl acetylenes, the primary homoquadricyclane products undergo a secondary photochemical rearangement leading to diaryl substituted tricyclo[3.2.1.0(4,6)]oct-2-enes. Mechanistic and photophysical studies suggest that photocycloaddition proceeds through an electrophilic triplet excited state whereas the subsequent rearrangement to the tricyclooctenes proceeds through a singlet excited state. Chemical and quantum yields for the cycloaddition, in general, correlate with the electron acceptor character of aryl substituents but are attenuated by photophysical factors, such as the competition between the conversion of acetylene singlet excited state into the reactive triplet excited states (intersystem crossing: ISC) and/or to the radical-anion (photoelectron transfer from the diene to the excited acetylene: PET). Dramatically enhanced ISC between pi-pi S(1) state and "phantom" n,pi triplet excited state is likely to be important in directing reactivity to the triplet pathway. The role of PET can be minimized by the judicious choice of reaction conditions (solvent, concentration, etc.). From a practical perspective, such reactions are interesting because "capping" of the triple bond with the polycyclic framework orients the terminal aryl (4-pyridyl, 4-tetrafluoropyridyl, phenyl, etc.) groups in an almost perfect 60 degrees angle and renders such molecules promising supramolecular building blocks, especially in the design of metal coordination polymers.     

Iron Carbonyl Induced Reactions of Norbornene Derivatives with Substituted Acetylenes

Photochemical reactions of norbornadiene with substituted acetylenes in the presence of Fe(CO)₅ gave various products of different types, depending on the nature of the acetylene. The results are summarized in Table 1. The cyclopentanone 1 was always formed in these reactions. In the reaction of disubstituted acetylenes such as dimethyl acetylenedicarboxylate and ethyl phenylpropiolate, the cyclopentenones 2 and 5 were formed, respectively. By contrast, propiolic esters produced the cyclohexenones 3 and 4 , in which the ester group was attached on the β carbon with respect to the keto group. Plausible mechanisms for the formation of these products are shown in Schemes 7 and 8. The reaction of diphenylacetylene gave the cyclohexendione 7 as well as the cyclopentenone 6 . Two enedione products 8 and 9 were obtained from the reaction of phenylacetylene. Compound 9 was converted to the aromatic diacetate 13 by heating with acetic anhydride in pyridine. On irradiation in the presence of Fe(CO)₅ norbornene reacted similarly with dimethyl acetylenedicarboxylate and phenylacetylene to give the cyclopentenone 14 and the cyclohexenone 15 , respectively. Compound 15 , upon heating, isomerized to hydroquinone 16 , which on acetylation gave the diacetate 17 .     

An ab initio molecular orbital study of the C2F2 species: The difluorovinylidene → difluoroacetylene rearrangement

An ab initio MO study, using medium size Gaussian basis sets has been made of vinylidene carbene, acetylene and the isomeric cyclic intermediate presumed to represent the transition state of their interconversion reaction, along with their perfluorinated analogs. The total energies of the acetylenes are lower than the vinylidenes and the estimated activation energy of their interconversion is considerably higher for the fluorinated molecules. The results are in line with experimental observations.     

钯催化偶联-消去法合成芳基末端炔的研究进展

钯催化偶联-消去法合成芳基末端炔的研究进展;芳炔;偶联反应;钯催化剂;合成;综述     

Synthesis of isoquinolines and pyridines by the palladium/copper-catalyzed coupling and cyclization of terminal acetylenes and unsaturated imines: the total synthesis of decumbenine B.

Monosubstituted isoquinolines and pyridines have been prepared in good to excellent yields via coupling of terminal acetylenes with the tert-butylimines of o-iodobenzaldehydes and 3-halo-2-alkenals in the presence of a palladium catalyst and subsequent copper-catalyzed cyclization of the intermediate iminoalkynes. In addition, isoquinoline heterocycles have been prepared in excellent yields via copper-catalyzed cyclization of iminoalkynes. The choice of cyclization conditions is dependent upon the nature of the terminal acetylene that is employed, as only aryl and alkenyl acetylenes cyclize under the palladium-catalyzed reaction conditions that have been developed. However, aryl-, vinylic-, and alkyl-substituted acetylenes undergo palladium-catalyzed coupling and subsequent copper-catalyzed cyclization in excellent yields. The total synthesis of the isoquinoline natural product decumbenine B has been accomplished in seven steps and 20% overall yield by employing this palladium-catalyzed coupling and cyclization methodology.     

双核钴簇合物(C6H5C2R)Co2(CO)6的合成

羰基钴簇合物Co₂(CO)₈可用于有机合成的催化剂。但Co₂(CO)₈本身不稳定,易被氧化。因此,研究不向CO₂簇合物的稳定性及其催化性能具有一定的意义。     

A simple synthesis of tetraethynylethenes and representative molecular structures of some dicobalt derivatives

Palladium–copper catalysed cross-coupling reactions of tetracholoroethene with terminal acetylenes RCCH (R=SiMe₃, C₆H₅, C₆H₄CN-4) in refluxing triethylamine afford the corresponding tetraethynylethenes in 30–60% isolated yields. The reaction of 1,6-bis(trimethylsilyl)-3,4-bis(trimethylsilylethynyl)-hex-3-ene-1,5-diyne with [Co₂(CO)₆(L₂)] [L₂=(CO)₂ or μ-dppm] affords complexes in which one or two (trans) acetylene moieties are coordinated by a dicobalt fragment.     

Reactions of diisobutyl- and diethylaluminum hydrides with α-acetylenes

Conclusions To obtain Al vinyl compounds R₂A1CH=CHR' by reacting R₂AlH with HC=CR', we must use weakly acid acetylenes (alkyl acetylenes) and perform the reaction in aliphatic hydrocarbons at a low temperature in excess acetylene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 910–912, April, 1968.     

Cross‐Metathesis of Terminal Alkynes

Terminal acetylenes are amongst the most problematic substrates for alkyne metathesis because they tend to undergo rapid polymerization on contact with a metal alkylidyne. The molybdenum complex 3 endowed with triphenylsilanolate ligands, however, is capable of inducing surprisingly effective cross‐metathesis reactions of terminal alkyl acetylenes with propynyl(trimethyl)silane to give products of type R¹?C?CSiMe . This unconventional way of introducing a silyl substituent onto an alkyne terminus complements the conventional tactics of deprotonation/silylation and excels as an orthogonal way of alkyne protecting group chemistry for substrates bearing base‐sensitive functionalities. Moreover, it is shown that even terminal aryl acetylenes can be cross‐metathesized with internal alkyne partners. These unprecedented transformations are compatible with various functional groups. The need to suppress acetylene formation, which seems to be a particularly effective catalyst poison, is also discussed.     

Free radicals in photolysis of mixed phosphonium–iodonium ylides and in their reactions with acetylenes

UV irradiation of mixed phosphonium–iodonium ylide in CH₂Cl₂ leads to formation of free radicals with lifetimes of a few minutes detected by EPR. In mixtures of ylides with acetylenes, the structure of radicals changes, and their concentration and stability increase. In the presence of acetylenes, the radicals contain ylide and acetylene residues, and their EPR spectra have hyperfine coupling constants typical for ³¹P nuclei in C-radicals and for ¹H nuclei, depending on the acetylene structure. It has been demonstrated that the observed radical products are formed from short-lived primary radicals.     

Electrophilic alkynylation: the dark side of acetylene chemistry

In addition to the well-established nucleophilic alkynylation, the use of electrophilic alkynes can expand tremendously the scope of acetylene transfer reactions. The use of metal catalysis has recently led to a rebirth of this research area. Halogenoalkynes, hypervalent alkynyliodoniums, acetylene sulfones and in situ oxidized terminal acetylenes are the most often used reagents for electrophilic alkynylation. Heteroatoms such as N, O, S and P can be now efficiently alkynylated. For C-C bond formation, electrophilic acetylenes can be coupled with different organometallic reagents. Recently, the first breakthrough in direct C-H and C[double bond, length as m-dash]C bond alkynylation has also been reported. Finally, sulfonyl acetylenes are efficient for alkyne transfer on carbon-centered radicals.     

Metal‐Free Activation of a C(sp)−H Bond of Aryl Acetylenes

C(sp)?H Bond activation of acetylene molecule still remains a challenge for synthetic organic chemists. In practice, acetylenes are activated by strong bases and metals. The first example for activating acetylenic protons under base and metal‐free conditions is reported here. It involves a general method for synthesizing propargylic derivatives of cotarnine. An array of tetrahydroisoquinolines alkaloids was synthesized by C(sp)?H bond activation of aromatic acetylenes with cotarnine at room temperature. A DFT‐based mechanism is proposed for the reaction.     

Investigation of the Reaction between 3‐Benzisothiazolones,an Isoindole Isoster and Activated Acetylenes: Synthesis of Heterocyclic Backbones for Building Bioactive Molecules

Investigation of the reaction between benzo[d]isothiazol‐3‐one, 2‐aminobenzo[d]isothiazol‐3‐one, its isoster 2‐aminoisoindolin‐1‐one, and activated acetylenes, in the presence of triphenylphosphine, led us to synthesize novel heterocyclic compounds that could be attractive for the building of biologically active molecules. A one‐pot PPh₃‐promoted tandem reaction, with acetylene dicarboxylates and dibenzoylacetylene, afforded new tricyclic pyrazolo‐fused benzisothiazoles. The PPh₃‐promoted reaction between benzisothiazolones and methyl propiolate afforded 1,4‐benzothiazepine‐5‐one derivatives, via an isothiazole ring expansion. These studies are providing additional insights in benzisothiazolone chemistry and describe simple and original synthetic accesses to novel derivatives.