Alkyne Equivalents Research Articles

ChemInform Abstract: Diels—Alder Reaction of Fused Pyran‐2‐ones with Ethyl Vinyl Ether.

AbstractEthyl vinyl ether (II) can be applied as a useful synthetic equivalent of acetylene in microwave‐assisted Diels—Alder reactions with fused pyran‐2‐ones.

Diels–Alder reaction of fused pyran-2-ones with ethyl vinyl ether

Ethyl vinyl ether was found to be an appropriate synthetic equivalent of acetylene for a set of Diels–Alder reactions with fused pyran-2-ones that yield fused carbocyclic systems. Transformations were conducted under microwave irradiation with DABCO (as a catalyst for the elimination of ethanol) and with n-butanol as the additive. A single-crystal X-ray diffraction structure is presented for N-(5,6,7,8-tetrahydro-6-methyl-8-oxonaphthalen-2-yl)benzamide.

Para-Selective Gold-Catalyzed Direct Alkynylation of Anilines

A method for the para-selective alkynylation of anilines is reported using AuCl as catalyst and triisopropylsilylethynyl-1,2-benziodoxol-3(1H)-one (TIPS-EBX) as an electrophilic acetylene equivalent. Para-alkynyl anilines substituted at positions 2 or 3 were obtained in one step from simple anilines under mild conditions (room temperature to 60 °C) under air. The methodology could also be extended to the alkynylation of trimethoxybenzenes.

Synthesis of Highly Stable 1,3-Diaryl-1H-1,2,3-triazol-5-ylidenes and Their Applications in Ruthenium-Catalyzed Olefin Metathesis

The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions.

ChemInform Abstract: Diversity‐Oriented Microwave‐Assisted Synthesis of the 3‐Benzazepine Framework.

AbstractTitle synthesis involves a microwave‐assisted three‐component reaction of an amine with an aldehyde and a terminal alkyne or two equivalents of alkyne, followed by Pd‐catalyzed microwave‐assisted cyclization.

Reactivity and Regioselectivity of Insertion of Unsaturated Molecules into M−C (M = Ir, Rh) Bonds of Cyclometalated Complexes

The reactivity of four different cyclometalated iridium and rhodium complexes (1, Ir−N−Me; 2, Rh−N−Me; 3, Ir−N−Py; 4, Rh−N−Py) with ancillary ligands with different electronic and steric properties has been investigated by reactions of ethylene (a), propylene (b), carbon monoxide (c), tert-butylisocyanide (d), acetylene (e), and phenylacetylene (f). Only coordination products were obtained for the reactions of ethylene and propylene with 1 and 3, while inserted and rearranged products were achieved for the reactions with 2 and 4. Insertion of a single equivalent of acetylene was observed for the reactions with 2, 3, and 4, whereas reaction with 1 produces a product in which 4 equiv of acetylene has undergone insertion. The reactions with carbon monoxide showed clean M−C bond insertion products, while tert-butylisocyanide formed only terminal adducts. Two equivalents of phenylacetylene were observed to insert for all of the cyclometalated complexes. The regioselectivity was also investigated for each cyclometalated complex by using a series of internal unsymmetrical alkynes, and the results revealed that the regioselectivity was controlled by both steric and electronic factors. The insertion compounds were fully characterized by 1H NMR spectroscopy, 13C NMR spectroscopy, elemental analysis, and X-ray determinations for selected cases.

ChemInform Abstract: Application of 3-Oxabicyclo(3.2.0)hept-6-ene-2,4-dione (Cyclobut-3-ene- 1,2-dicarboxylic Anhydride) as an Acetylene Equivalent in Cycloadditions.

The effectiveness and limitations of dioxo-3-oxabicyclo[3.2.0]hept-6-ene-2,4-dione (cyclobut-3ene-1,2-dicarboxylic anhydride) as an acetylene equivalent in both 1,3-dipolar and Diels–Alder cycloadditions is reported; it reacted readily with a variety of reagents, including N-benzylideneaniline N-oxide, nitrile oxides, diazomethane, cyclopentadiene, tetracyclone, anthracene, 1,2,5-triphenylphosphole 1-oxide and 1,3-diphenylisobenzofuran. The structures and stereochemistry of the adducts were deduced from their NMR data; in all cases, the sterically favoured anti-isomers are formed exclusively. The configuration of the Diels–Alder adducts are assigned as endo with the exception of that from tetracyclone (and possibly 1,3-diphenylisobenzofuran) for which an exo-structure is assumed on the basis of steric arguments. Adducts were not obtained with several other reagents; possible reasons for this lack of reactivity are discussed. When subjected to flash vacuum pyrolysis, the adducts underwent thermal fragmentation, either by a retro-cleavage, or by loss of maleic anhydride to form products that are derived formally from reaction of acetylene in the cycloaddition step. A concerted pathway is proposed for the pyrolytic conversion into the ‘formal acetylene cycloadduct’ rather than a stepwise radical mechanism.

ChemInform Abstract: Commercially Available Liquid Enol Ethers and Acetates as Gaseous Alkyne Equivalents in Cationic Rh(I)/BINAP-Catalyzed Chemo- and Regioselective Formal Cross-Alkyne Cyclotrimerizations.

ChemInform Abstract: Commercially Available Liquid Enol Ethers and Acetates as Gaseous Alkyne Equivalents in Cationic Rh(I)/BINAP-Catalyzed Chemo- and Regioselective Formal Cross-Alkyne Cyclotrimerizations.

ChemInform Abstract: Commercially Available Liquid Enol Ethers and Acetates as Gaseous Alkyne Equivalents in Cationic Rh(I)/BINAP‐Catalyzed Chemo‐ and Regioselective Formal Cross‐Alkyne Cyclotrimerizations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Commercially available liquid enol ethers and acetates as gaseous alkyne equivalents in cationic Rh(I)/BINAP-catalyzed chemo- and regioselective formal cross-alkyne cyclotrimerizations

A cationic rhodium(I)/BINAP complex catalyzes partial intramolecular [2+2+2] cycloadditions of 1,6- and 1,7-diynes with enol ethers or a ketene acetal giving substituted benzenes in good yields. The same catalyst also catalyzes complete intermolecular [2+2+2] cycloadditions of two different monoynes with enol acetates giving tri- and tetrasubstituted benzenes in good yields with complete regioselectivity. Commercially available liquid enol ethers and acetates can be used as versatile equivalents for gaseous alkynes in the present rhodium-catalyzed formal cross-alkyne cyclotrimerizations.

ChemInform Abstract: Ethyl Vinyl Ether as a Synthetic Equivalent of Acetylene in a DABCO‐Catalyzed Microwave‐Assisted Diels—Alder—Elimination Reaction Sequence Starting from 2H‐Pyran‐2‐ones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Bis‐sulfonyl Ethylene as Masked Acetylene Equivalent in Catalytic Asymmetric [3 + 2] Cycloaddition of Azomethine Ylides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Liquid Enol Ethers and Acetates as Gaseous Alkyne Equivalents in Rh‐Catalyzed Chemo‐ and Regioselective Formal Cross‐Alkyne Cyclotrimerization.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cross-Alkyne Cyclotrimerization Using Liquid Enol Ethers and Acetates

Cheap liquid enol ethers and acetates were successfully used as gaseous alkyne equivalents in formal cross-cyclotrimerizations. The corresponding reactions proceeded under mild conditions with perfect regioselectivities for both cycloadditions involving 1,6-diynes and two different monoynes.

Bis-Sulfonyl Ethylene as Masked Acetylene Equivalent in Catalytic Asymmetric [3 + 2] Cycloaddition of Azomethine Ylides

Enantioenriched 3-pyrrolines have been synthesized by highly enantioselective Fesulphos-Cu-catalyzed 1,3-dipolar cycloaddition of azomethine ylides with trans-1,2-bisphenylsulfonyl ethylene, followed by reductive sulfonyl elimination. High levels of reactivity, exoselectivity, and enantioselectivity have been accomplished for a variety of substituted azomethine ylides. This cycloaddition-desulfonylation strategy has been applied as a key step in the enantioselective synthesis of a biologically active C-azanucleoside.

Liquid Enol Ethers and Acetates as Gaseous Alkyne Equivalents in Rh-Catalyzed Chemo- and Regioselective Formal Cross-Alkyne Cyclotrimerization

A cationic rhodium(I)/rac-BINAP complex catalyzes chemo- and regioselective formal cross-cyclotrimerizations of alkynes with enol ethers or acetates. Commercially available and cheap liquid enol ethers and acetates could be used as convenient gaseous alkyne equivalents in the present rhodium catalyses.

Imido-Alkyne Coupling in Titanium Complexes: New Insights into the Alkyne Hydroamination Reaction

Titanium imido complexes [Ti(NR)(N2ArNpy)(L)] (N2ArNpy = MeC(2-C5H4N)(CH2NAr)2, Ar = 4-C6H4Me or 3,5-C6H3Me2) have been prepared from the corresponding bis(amide) complexes [Ti(N2ArNpy)(NMe2)2]. The reaction chemistry of the imido ligand has been investigated with aryl acetylenes, affording the {2 + 2} cycloaddition products [Ti(N2ArNpy){κ2-N(tBu)CHCAr‘}] (Ar‘ = Ph and 4-C6H4Me) which represent a catalytic intermediate in the anti-Markovnikov hydroamination of terminal alkynes. Reaction of these azatitanacyclobutene complexes with tert-butylamine completes the catalytic cycle, affording trans-cinnamyl(tert-butyl)amine; conversely, reaction with a second equivalent of alkyne afforded a second insertion product, an azatitanacyclohexadiene [Ti(N2ArNpy){κ2-N(tBu)CHC(Ar‘)C(Ar‘) = CH}], two examples of which have been characterized by X-ray crystallography. Studies into the catalytic hydroamination of phenyl acetylene with tert-butylamine have been performed and indicate that the formation of an azatitanacyclohexadiene complex represents a deactivation pathway in this catalytic reaction.

Synthesis of Indeno-Fused Aromatics by [2+2+2] Cycloaddition

The rhodium-catalyzed [2+2+2] cycloaddition of diynes and alkynes is employed as the key step in an efficient and modular synthesis of fluoranthenes and indenocorannulenes. The success of the rhodium-catalyzed cycloaddition for the construction of such sterically crowded products is worthy of note (see review below for a discussion of metal-catalyzed [2+2+2] reactions). This protocol is compatible with substrates bearing useful functional groups, including esters, alcohols, and aryl halides. The ability to carry out high-yielding formal [2+2+2] reactions of acetylene using norbornadiene as an acetylene equivalent is of considerable interest from the standpoint of ease of operation and safety.

Carbon-nitrogen bond formation via the reaction of terminal alkynes with a dinuclear side-on dinitrogen complex.

The dinuclear dinitrogen complex ([P2N2]Zr)2(mu-eta2:eta2-N2) reacts with terminal aryl alkynes to generate a new species in which the dinitrogen unit has been functionalized. The products formed have the general formula ([P2N2]Zr)2(mu-eta2:eta2-N2CCAr)(mu-CCAr) and display a styryl-hydrazido unit bridging the two Zr centers along with a bridging arylalkynide. The crystal structures of three of these products are reported. A mechanism is proposed for this process that involves cycloaddition of the alkyne to the side-on dinitrogen unit followed by protonation of the Zr-C bond by a second equivalent of terminal alkyne. A fluxional process is operative in solution that equilibrates the phosphorus nuclei at high temperature; in the slow exchange limit, the two [P2N2]Zr ends of complex are inequivalent as evidenced by four resonances in the 31P NMR spectrum for the inequivalent phosphorus donors. This C-N bond-forming reaction is unique in that an activated dinitrogen fragment undergoes a reaction with an alkyne.

An efficient synthesis of cytostatic mono and bis-alkynylpyrimidine derivatives by the Sonogashira cross-coupling reactions of 2,4-diamino-6-iodopyrimidine and 2-amino-4,6-dichloropyrimidine

A series of 6-alkynyl-2,4-diaminopyrimidine derivatives bearing various substituents at alkynyl moiety was prepared by the Sonogashira cross-coupling reaction of 2,4-diamino-6-iodopyrimidine using Pd(PPh3)2Cl2 as catalyst. The same reaction was applied to 2-amino-4,6-dichloropyrimidine. This compound on reaction with 1 equiv. of alkyne gave 6-alkynyl-2-amino-4-chloropyrimidine derivatives as main products, while reaction with three equivalents of alkyne afforded predominantly 4,6-bis-alkynyl-2-aminopyrimidines. Some of the resulting alkynyl pyrimidines showed considerable cytostatic activity.