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Synthesis

Ramped-up route to polyrotaxanes

Iterative process threads multiple rings onto molecule’s axle with high yields

by Bethany Halford
October 17, 2016 | APPEARED IN VOLUME 94, ISSUE 41

Making the mechanically interlocked molecules known as polyrotaxanes—wherein multiple macrocycles encircle a central oligomeric axle with bulky end groups—offers synthetic chemists an interesting challenge. An iterative rotaxane synthesis developed by the University of Southampton’s Stephen Goldup and colleagues now allows chemists to fashion such compounds in high yield and with the ability to use different macrocycles in the same polyrotaxane (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b08958). The method makes use of the copper-mediated alkyne-azide cycloaddition reaction, often referred to as click chemistry. Goldup and coworkers used a templating procedure to click together an alkyne and an azide within the cavity of a macrocycle, creating a triazole at the core of their rotaxane. Because the aromatic ring that contains the starting azide also contains a protected alkyne, the chemists are able to remove the protecting group and repeat the process over and over again. Goldup’s team made a polyrotaxane containing five of the same macrocycle moieties using this procedure, forming each new mechanical bond in 90% yield. They also used the method to thread three different kinds of macrocycle onto the same axle moiety in a specified order.

Credit: J. Am. Chem. Soc.
A polyrotaxane made via an iterative click-chemistry process.
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