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Unexpected Reactions of Terminal Alkynes in Targeted “Click Chemistry’’ Coppercatalyzed Azide-alkyne Cycloadditions

Author(s):

Tammar Hussein Ali*, Thorsten Heidelberg*, Rusnah Syahila Duali Hussen and Hairul Anuar Tajuddin   Pages 1 - 6 ( 6 )

Abstract:


Background: High efficiency in terms of reactions yield and purity has led to the extensive utilization of the copper catalyzed azide alkyne cycloaddition (CuAAC) in various fields of chemistry. Its compatibility with low molecular weight alcohols promotes the application in surfactant synthesis to tackle miscibility constraints of the reactants.

Objective: Aiming for the tuning of surfactant properties, double click coupling of the antipode precursors was attempted. Failure of the CuAAC to provide the targeted product in combination with unexpected reaction outputs leading to an investigation of the side reaction.

Results: The Cu(I)-catalyst applied for azide alkyne cycloadditions enables a homo-coupling of certain terminal alkyne at higher temperature. Moreover, aromatic propargyl ethers may be cleaved to furnish the corresponding phenol. The copper-catalyzed coupling appeared highly sensitive towards the alkyne compound. Only selected derivatives of propargyl alcohol were successfully dimerized.

Conclusions: The observed failure of the Huisgen reaction for the synthesis of sugar-based surfactants may indicate non-recognized constrains of the reaction, which could affect its wide application for bioconjugation. The temperature requirement for the alternative dimerization of terminal alkynes renders this side reaction non-relevant for typical click couplings, while the narrow substrate diversity and moderate yield limit its synthetic application.

Keywords:

Click Chemistry; Huisgen cycloaddition; alkyne dimerization; aryl-propargyl ether cleavage; Copper azide alkyne cycloaddition (CuAAC); depropargylation.

Affiliation:

Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur



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