Template synthesis of rotaxanes with carbamate-linked axles

Abstract

Non-ionic template effects [1] proved to be a successful concept to synthesize supramolecular architectures [2], especially hydrogen bond-mediated catenane [3] and rotaxane [4] formation [5].In the beginning aromatic diacid dichlorides were believed to be the guests to fit into tetralactame macrocycles. Reaction with bulky amine stoppers in the presence of a macrocycle led to amide-based rotaxanes. Yet by replacing the aromatic diacid dichloride "guests" with aliphatic ones it was even possible to synthesize amidebased rotaxanes with aliphatic building blocks [6] Abstract. Proceeding from diisocyanates 4 and 10 -13, (4-hydroxyphenyl)triphenylmethane 14 and tetralactame macrocycles 1, 2 and 9 the threading synthesis of rotaxanes 16 -21 containing carbamate units in the axle is described. In addition to aromatic diisocyanates aliphatic ones are firstly π-stacking seemed not to be necessary for rotaxane formation. In 1997 we were able to introduce diisocyanates [7] as building blocks. Treatment of macrocycles 1 [8] and 2 [9] with diisocyanates 3 and 4 and further reaction with bulky amine stoppers 5 led to rotaxanes 6 -8 with urea-linked axles [10] in 4 -11% yield (Scheme 1). First attempts to synthesize these rotaxanes at room temperature failed, so we raised the reaction temperature to 40 °C. Although a rise of temperature is weakening the hydrogen bonds [11] between macrocyclic amide host and carbonylic guest, we were able to creintroduced as building blocks in rotaxane chemistry. The template synthesis of the new tetralactame macrocycle 9 with a pyridine unit is presented. It is used as wheel in a rotaxane synthesis towards the carbamate-linked rotaxane 21.Scheme 1 Synthesis of rotaxanes containing urea-linked axles 542