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Keywords:

  • Diels–Alder reaction;
  • host–guest systems;
  • pyridazine;
  • rotaxanes;
  • solvent-free synthesis
Thumbnail image of graphical abstract

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.