“Click” Chemistry: Application of Copper Metal in Cu-Catalyzed Azomethine Imine–Alkyne Cycloadditions

Kirar, Eva Pušavec; Grošelj, Uroš; Mirri, Giorgio; Požgan, Franc; Strle, Gregor; Štefane, Bogdan; Jovanovski, Vasko; Svete, Jurij

doi:10.1021/acs.joc.6b00945

Cited by 30 publications

(24 citation statements)

References 59 publications

(62 reference statements)

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“…In the absence of firm experimental and theoretical proofs, the generally accepted plausible mechanism is based on the catalytic Cu(I) acetylide as the reactive species, which undergoes cycloaddition, followed by protonation of the cuprated cycloadduct. 22,24,28,29,31,[33][34][35]37,38,42,45,46 This reaction pathway is supported by experiments performed with copper(I) acetylides, deuterated acetylenes, and/or proton sources, such as D 2 O and AcOD. 29,[33][34][35]38 Copper(I) was, either used directly, 29,33 or formed in situ by reduction of Cu(II) 34,35 or by oxidation of Cu(0).…”

Section: The Mechanism Of the Cuaiac Reactionmentioning

confidence: 93%

“…In the presence of DIPEA, copper powder showed no catalytic activity (Scheme 21). 38 Applicability of CuAIAC in fluorescent labelling has been demonstrated by performing the reaction with polymerbound reactants. Thus, treatment of chloromethylated polystyrene (Merrifield resin 68) with propynoic acid in the presence of KI and a base gave the polymer-bound propynoate 69, which was reacted with a solution of azomethine imine 53 in CH 2 Cl 2 in the presence of a cluster of copper wires to furnish a fluorescent polymer-bound cycloadduct 70.…”

Section: Review Syn Thesismentioning

confidence: 99%

“…In another approach, treatment of formyl-polystyrene 71 with 5,5-dimethylpyrazolidin-3-one (72) afforded polymer-bound azomethine imine 73, which was treated further with a solution of methyl propynoate (7c) in dichloromethane in the presence of a copper wire to give another fluorescent polymer-bound cycloadduct 74 (Scheme 22). 38 Finally, Cu powder also turned to be a superior catalyst over CuI or CuI/DIPEA in cycloadditions to racemic 4-acylamino-substituted pyrazolidin-1-ium-2-ides 57 to conjugated acetylenes 7. High yields of cycloadducts 61 and 62…”

Section: Review Syn Thesismentioning

confidence: 99%

“…29,[33][34][35]38 Copper(I) was, either used directly, 29,33 or formed in situ by reduction of Cu(II) 34,35 or by oxidation of Cu(0). 38 Scheme 46 shows a generally accepted catalytic cycle of the CuAIAC reaction which is based on a concerted cycloaddition mechanism. The reaction starts with the formation of a Cu(I) species, available from Cu(0), Cu(I), or Cu(II), which deprotonates the terminal acetylene 7 to give the soluble catalytic acetylide 7-Cu.…”

Section: The Mechanism Of the Cuaiac Reactionmentioning

confidence: 99%

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Copper-Catalyzed Azomethine Imine–Alkyne Cycloadditions (CuAIAC)

Grošelj

Požgan²,

Štefane³

et al. 2018

Synthesis

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Although the first example of copper-catalyzed azomethine imine–alkyne cycloaddition (CuAIAC) was published only a year after the seminal papers of Meldal and Sharpless on Cu-catalyzed azide–alkyne cycloaddition (CuAAC), the CuAIAC reaction has remained overlooked by the synthetic community for almost a decade. Since 2010, however, CuAIAC reaction started to emerge as a promising supplement to the well-known CuAAC reaction. The present review surveys primarily the literature on CuAIAC reaction since 2003. Beside this, azomethine imine–alkyne cycloadditions catalyzed by other metals, selected examples of metal-free reactions, and related [3+3] and [3+4] cycloadditions of azomethine imines are presented. All these experimental data indicate the viability of CuAIAC in organic synthesis and the applicability in ‘click’ chemistry.1 Introduction2 Reactions with Acyclic Azomethine Imines3 Reactions with C,N-Cyclic Azomethine Imines4 Reactions with N,N-Cyclic Azomethine Imines5 Reactions with C,N,N-Cyclic Azomethine Imines6 The Mechanism of the CuAIAC Reaction7 Conclusions and Outlook

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Section: The Mechanism Of the Cuaiac Reactionmentioning

confidence: 93%

Section: Review Syn Thesismentioning

confidence: 99%

Section: Review Syn Thesismentioning

confidence: 99%

Section: The Mechanism Of the Cuaiac Reactionmentioning

confidence: 99%

See 2 more Smart Citations

Copper-Catalyzed Azomethine Imine–Alkyne Cycloadditions (CuAIAC)

Grošelj

Požgan²,

Štefane³

et al. 2018

Synthesis

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“…This chemistry serves as a path to design materials by making use of adequate building blocks containing azide and alkyne terminals to “click” together . Researchers have utilized these reactions for the synthesis of a wide variety of molecular architectures . The mechanism of these reactions is now fairly well understood .…”

Section: Introductionmentioning

confidence: 99%

Azide telechelics chain extended by click reaction: Synthesis, characterization, and cross‐linking

Sunitha

Unnikrishnan

Nair

2018

Polymers for Advanced Techs

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Azide telechelics of poly(dimethylsiloxane) (PDMS), polypropylene oxide (PPO), and polyethylene oxide (PEO) were synthesized from the corresponding epoxy telechelics and characterized. These oligomeric azides were chain extended by reaction with bispropargyl ether of bisphenol A (BPEBA) through a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. PDMS manifested a faster reaction in contrast to PPO or PEO. The chain-extended polymers underwent cross-linking above 170°C through thermal cleavage of residual (terminal) azide groups. This was manifested in their rheograms and was further substantiated by FTIR and NMR spectroscopic analyses. Dynamic mechanical analyses of the cross-linked polymers exhibited characteristic transitions of hard and soft segments, implying microphase separation in the system. Microscopic evaluation of the thermally cross-linked sample revealed a porous morphology with microsized to nanosized pores. KEYWORDS azide telechelics, propargyl ether, thermal cross-linking, triazole, click reaction 1 | INTRODUCTION Telechelic polymers evince a lot of interest because of their various applications such as precursors for the synthesis of multiblock copolymers and synthesis aid for a large number of branched and complex polymeric structures. 1,2 For example, hydroxyl-terminated polybutadiene (HTPB) is a well-known telechelic system used as a propellant binder and as adhesive, sealant, elastomer, 3 etc. End-functional poly(dimethylsiloxane) (PDMS) is another example of a very useful synthesis intermediate widely used in adhesives, sealants, and coatings formulations 4 in space research. The possibility to externally steer the morphology and the associated physical properties of telechelic polymers renders them important and versatile building blocks for modern materials science. 2,3Diverse methods such as anionic, cationic, ring opening, group transfer, free radical, step-growth polymerization, and chain scission processes are adopted for the syntheses of these telechelic polymers. [5][6][7][8] The criticality in synthesis of telechelic polymers lies in the quantitative introduction and subsequent conversion of the functional group at the chain ends. Living polymerization technique is a good technique for getting telechelic polymers with narrow molecular weight distribution. 9,10 However, the properties of polymers obtained by end-linking of telechelic oligomers depend strongly on stoichiometry, side reactions, extent of conversion, etc. The relative reactivities of the groups, substitution effects, side groups, etc play a major role 11,12 in deciding the success factor. Different types of synthesis strategies such as Diels-Alder, [13][14][15] thiol-ene, [16][17][18][19] and azide-alkyne 20,21 figure under the title of "click chemistry." Of these, the Diels-Alder belongs to a class of thermoreversible reactions. 22 Copper-catalyzed azide-alkyne cyclo addition (CuAAC) is shown to be the most effective and versatile, since it is highly specific and efficient, requires mild conditions, 23 has ...

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[3 + 2] Cycloadditions of Azomethine Imines

Grošelj

Svete

2020

Organic Reactions

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In spite of their late discovery in the middle of 20 th century, the importance of azomethine imines and their [3+2] cycloaddition reactions has grown constantly throughout the decades. Today, [3+2] cycloadditions of azomethine imines have become indispensable in the preparation of pyrazole derivatives with all degrees of saturation. The structural diversity of azomethine imines is wide and comprises acyclic, C , N ‐cyclic, N , N ‐cyclic, and C , N , N ‐cyclic 1,3‐dipoles. Although electron‐deficient dipolarophiles are preferred, electron‐rich dipolarophiles, such as enol ethers and enamines, are also commonly used in these reactions. Compared to cyclocondensation methods and [3+2] cycloadditions with diazoalkanes and nitrile imines, [3+2] cycloadditions with azomethine imines provide access to a greater diversity of pyrazole derivatives with all degrees of saturation. As with other 1,3‐dipolar cycloadditions, a concerted and nearly synchronous mechanism has been proposed for most [3+2] cycloadditions of azomethine imines, although a stepwise mechanism may be viable in some cases. Several examples of asymmetric [3+2] cycloadditions of azomethine imines that afford non‐racemic cycloadducts with high enantioselectivity have been reported. These asymmetric cycloadditions are performed with various types of transition metal catalysts and organocatalysts, and indicate their potential for the asymmetric synthesis of saturated pyrazole derivatives. Finally, many examples of copper‐catalyzed and thermal, strain‐promoted [3+2] cycloadditions of azomethine imines (in particular sydnones) clearly indicate wide applicability of these reactions in bioconjugation, fluorescent labelling, materials functionalization, and other applications outside the realm of pure organic synthesis.

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“Click” Chemistry: Application of Copper Metal in Cu-Catalyzed Azomethine Imine–Alkyne Cycloadditions

Cited by 30 publications

References 59 publications

Copper-Catalyzed Azomethine Imine–Alkyne Cycloadditions (CuAIAC)

Copper-Catalyzed Azomethine Imine–Alkyne Cycloadditions (CuAIAC)

Azide telechelics chain extended by click reaction: Synthesis, characterization, and cross‐linking

[3 + 2] Cycloadditions of Azomethine Imines

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