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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The Diels-Alder reactions of five fluorine-containing dienophiles with cyelopentadiene, butadiene and anthracene have been investigated. An adduct was obtained in all cases except in the reaction between allyl fluoride and butadiene. Qualitatively, the relative order of reactivity was found to be: CF3CF=CF2 > C2FjCH=CHj > CF3CH=CH2 > CH2FCH=CH2 > CF,C(CH3)=CH2.

Klein und fein: Das auf SiO2 gebildete [2]Pseudorotaxan aus Dipropargylammonium‐tetrafluoroborat und dem Kronenether [21]Krone‐7 wurde in einem Kugelmahlverfahren mit 1,2,4,5‐Tetrazin‐Stoppern verschlossen (siehe Röntgenstrukturanalyse). Nach dieser effizienten lösungsmittelfreien Reaktion konnte das kleinste bekannte [2]Rotaxan in 81 % Ausbeute isoliert werden.

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