Azide-alkyne Huisgen cycloaddition: Difference between revisions

Revision as of 15:20, 28 June 2016

Revision as of 13:44, 5 July 2016

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| author = Huisgen, R. | doi = 10.1039/PS9610000357}}

</ref> was the first to understand the scope of this [[organic reaction]]. American [[chemist]] [[K. Barry Sharpless]] has referred to this [[cycloaddition]] as "the cream of the crop" of [[click chemistry]]<ref>

{{cite journal | authorauthors = H. C. Kolb, M. G. Finn and K. B. Sharpless | title = Click Chemistry: Diverse Chemical Function from a Few Good Reactions | year = 2001 | journal = [[Angewandte Chemie International Edition]] | volume = 40 | issue = 11 | pages = 2004–2021 | doi = 10.1002/1521-3773(20010601)40:11<2004::AID-ANIE2004>3.0.CO;2-5 | pmid=11433435}}

</ref> and "the premier example of a click reaction."<ref>{{cite journal|last=Kolb|first=H.C.|author2=Sharpless, B.K.|title=The growing impact of click chemistry on drug discovery|year=2003|volume=8|issue=24|pages=1128–1137|doi=10.1016/S1359-6446(03)02933-7|pmid=14678739|journal=Drug Discov Today}}</ref>

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| doi = 10.1039/b507776a

| title = Click-chemistry as an efficient synthetic tool for the preparation of novel conjugated polymers

| authorauthors = D. J. V. C. van Steenis, O. R. P. David, G. P. F. van Strijdonck, J. H. van Maarseveen and J. N. H. Reek

| pmid = 16113739

| issue = 34}}

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| doi = 10.1039/b508428h

| title = Preparation of biohybrid amphiphiles via the copper catalysed Huisgen [3 + 2] dipolar cycloaddition reaction

| authorauthors = A. J. Dirks, S. S. van Berkel, N. S. Hatzakis, J. A. Opsteen, F. L. van Delft, J. J. L. M. Cornelissen, A. E. Rowan, J. C. M. van Hest, F. P. J. T. Rutjes, R. J. M. Nolte

| pmid = 16100593

| issue = 33}}

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The proposed mechanism suggests that in the first step, the [[spectator ligand]]s undergo displacement reaction to produce an [[activated complex]] which is converted, via [[oxidative coupling]] of an alkyne and an azide to the ruthenium containing metallocyle (Ruthenacycle). The new [[carbon-nitrogen bond|C-N bond]] is formed between the more electronegative and less sterically demanding carbon of the alkyne and the terminal nitrogen of the azide. The metallacycle intermediate then undergoes reductive elimination releasing the aromatic triazole product and regenerating the catalyst or the activated complex for further reaction cycles.

Cp^*RuCl(PPh₃)₂, Cp^*Ru(COD)and Cp^*[RuCl₄] are commonly used ruthenium catalysts. Catalysts containing cyclopentadienyl(Cp) group are also used. However, better results are observed with the pentamethylcyclopentadienyl(Cp^*) version. This may be due to the sterically demanding Cp^* group which facilitates the displacement of the spectator ligands.<ref>{{cite journal | authorauthors = Li Zhang, Xinguo Chen, Peng Xue, Herman H. Y. Sun, Ian D. Williams, K. Barry Sharpless, Valery V. Fokin, and Guochen Jia; |lastauthoramp=yes | title = Ruthenium-Catalyzed Cycloaddition of Alkynes and Organic Azides | year = 2005| journal = [[J. Am. Chem. Soc.]] | volume = 127 | issue = 46 | pages = 15998–15999 | doi = 10.1021/ja054114s | pmid = 16287266}}</ref><ref>{{cite journal |author1=Brant C. Boren |author2=Sridhar Narayan |author3=Lars K. Rasmussen |author4=Li Zhang |author5=Haitao Zhao |author6=Zhenyang Lin |author7=Guochen Jia |author8=Valery V. Fokin | title = Ruthenium-Catalyzed Azide−Alkyne Cycloaddition: Scope and Mechanism | year = 2008| journal = [[J. Am. Chem. Soc.]] | volume = 130 | issue = 28 | pages = 8923–8930 | doi = 10.1021/ja0749993 | pmid = 18570425}}</ref>

[[Image:RuAAC mechanism.png|center|450px|Mechanism for ruthenium-catalysed click chemistry]]

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</ref>

Curiously, pre-formed silver acetylides do not react with azides; however, silver acetylides do react with azides under catalysis with copper(I).<ref>

{{cite journal | authorauthors = Proietti Silvestri, I., Andemarian, F., Khairallah, G.N., Yap, S., Quach, T., Tsegay, S., Williams, C.M., O'Hair, R.A.J., Donnelly, P.S., Williams, S.J.| title = Copper(i)-catalyzed cycloaddition of silver acetylides and azides: Incorporation of volatile acetylenes into the triazole core | year = 2011 | journal = [[Organic and Biomolecular Chemistry]] | volume = 9 | issue = 17 | pages = 6082–6088 | doi = 10.1039/c1ob05360d | pmid= 21748192}}

</ref>