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Small is beautiful: The [2]pseudorotaxane formed from dipropargylammonium tetrafluoroborate and the crown ether [21]crown-7 on SiO2 was stoppered with 1,2,4,5-tetrazine in a ball-milling process (see X-ray structure). This new and efficient solvent-free reaction led to the isolation in high yield (81 %) of the smallest [2]rotaxane reported to date.
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Hsu et al. (2008) studied this question.
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