ChemInform Abstract: Alkyne—Azide Cycloaddition Catalyzed by Fe—Cu Nanoparticles.
Ángel García-MuñozJaime GonzálezJessica Trujillo‐ReyesRaúl A. Morales‐LuckieVíctor Sánchez‐MendietaCarlos GonzálezAydeé FuentesErick Cuevas‐Yáñez
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Abstract Paramagnetic Fe—Cu nanoparticles are used to catalyze typical azide—alkyne cycloadditions.Keywords:
Alkyne
Gold(I) chloride (stabilized by tetrahydrothiophene) reacts with the cycloheptynes 3,3,6,6-tetramethyl-1-thiacyclohept-4-yne-1,1-dioxide (SO2-alkyne) and 3,3,6,6-tetramethyl-1-thiacyclohept-4-yne (S-alkyne) to afford the complexes [(η2-alkyne)AuCl]n [n = 2 (SO2-alkyne), n = ∞ (S-alkyne)]; the X-ray structures of both compounds show trigonal-planar gold(I) centres and very short Au–C(alkyne) bonds.
Alkyne
Tetrahydrothiophene
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Alkyne
Aromatization
Enyne
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The room temperature 1,3-dipolar cycloaddition reactions of the boron azide, Cy2BN3 with the electron-poor acetylenes RCO2CCCO2R, EtCCCOMe and HCCP(O)Ph2 afforded new 1,2,3-triazoles. In the case of RCO2CCCO2R, a new macrocyclic product was isolated with loss of the R group.
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The enantioselective N-heterocyclic carbene-catalysed formal 2+2- and 2+2+2- cycloadditions of ketenes with isothiocyanates can be investigated. At room temperature, the reaction of N-arylthiocyanates favours the 2+2-cycloaddition. However, at −40°C, N-benzoylisothiocyanates undergo the 2+2+2-cycloaddition. This chapter discusses cycloaddition-type addition reactions. Specifically, it covers three types of cycloadditions: 2+2-cycloaddition, 2+3-cycloaddition and 2+4-cycloaddition. Miscellaneous cycloaddition reactions are separately described at the end of the chapter.
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This brief review article describes the progress made in the synthesis of 1,2,3-triazole-fused heterocycles, over the last ten years, mainly by azide-alkyne cycloaddition reactions. In this article, the emphasis is on the various aspects of 1,3-dipolar cycloaddition reactions, especially intramolecular azide-alkyne dipolar cycloaddition reactions.
Alkyne
Triazole
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The novel "double strained alkyne" 3 has been prepared and evaluated in strain-promoted azide-alkyne cycloaddition reactions with azides. The X-ray crystallographic structure of 3, which was prepared in one step from 1,1'-biphenyl-2,2',6,6'-tetrol 4, reveals the strained nature of the alkynes. Dialkyne 3 undergoes cycloaddition reactions with a number of azides, giving mixtures of regiosiomeric products in excellent yields. The monoaddition products were not observed or isolated from the reactions, suggesting that the second cycloaddition proceeds at a faster rate than the first, and this is supported by molecular modeling studies. Dialkyne 3 was successfully employed for "peptide stapling" of a p53-based diazido peptide, whereby two azides are bridged to give a product with a stabilized conformation.
Alkyne
Biphenyl
Reactivity
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Abstract 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
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The use of the bulky hydrotris(3-mesitylpyrazolyl)borate anionic ligand has allowed the synthesis of stable TpMsCu(alkyne) complexes (alkyne = 1-hexyne, 1, phenylacetylene, 2, and ethyl propiolate, 3). The spectroscopic and structural features of these compounds and their relative reactivity have been examined, indicating the existence of a low π back-bonding from the copper(I) centre to the alkyne. Ligand exchange experiments have shown that terminal alkyne adducts are more stable than internal alkyne analogues. In good accordance with this, the previously reported alkyne cyclopropenation reaction catalysed by the TpxCu complexes can be rationalized and correlated with their relative stability.
Alkyne
Phenylacetylene
Reactivity
Diphenylacetylene
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Abstract Acetylene and ethylene are the smallest molecules that contain an unsaturated carbon–carbon bond and can be efficiently utilized in a large variety of cycloaddition reactions. In this review, we summarize the application of these C2 molecular units in cycloaddition chemistry and highlight their amazing synthetic opportunities. 1 Introduction 2 Fundamental Features and Differences of Cycloaddition Reactions Involving Acetylene and Ethylene 3 (2+1) Cycloaddition 4 [2+2] Cycloaddition 5 (3+2) Cycloaddition 6 [4+2] Cycloaddition 7 (2+2+1) Cycloaddition 8 [2+2+2] Cycloaddition 9 The Use of Acetylene and Ethylene Cycloaddition for Deuterium and 13C Labeling 10 Conclusions
Acetylene
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This Chapter Contains Sections titled: 2 + 2-Cycloaddition 2 + 3-Cycloaddition 2 + 4-Cycloaddition Miscellaneous Cycloadditions References A review of advances in Nickel-catalysed cycloaddition reactions directed towards the synthesis of carbocycles and heterocycles has been presented. The discussion includes the development and mechanistic studies of the Ni/NHC catalysts that couple diynes and nitriles to form pyridines. The use of vinyl cyclopropanes, aldehydes, ketones, tropones, 3-azetidinones, and 3-oxetenones as substrates in new Ni-catalysed cycloaddition reactions is also discussed. A second extensive review concerning Ni-catalysed cycloaddition reactions that have been studied since 2004 has been published. 1,3-Dipolar cycloadditions, Diels-Alder cycloadditions, 2+2+2- cycloadditions, and 3+3-cycloadditions are discussed. NHC-stabilized silylene monohydride reacted with diphenylacetylene to yield a 2,3,4,5-tetraphenyl-1-(tri-t-butylsilyl)-1H-silole via a 2+2+1-cycloaddition. DFT calculations indicate that the reaction mechanism did not include a silirene, the typical 2+1-cycloaddition product. The Rhodium-catalysed enantioselective 2+2+2-cycloaddition of silicon-containing prochiral triynes and internal alkynes yielded silicon-stereogenic dibenzosiloles with high enantoselectivities and high yields.
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Diphenylacetylene
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