Recent advances in the synthesis of ammonium-based rotaxanes

Abstract

The number of synthetic methods enabling the preparation of ammonium-based rotaxanes has increased very rapidly in the past ten years. The challenge in the synthesis of rotaxanes results from the rather weak interactions between the ammonium-containing rod and the crown ether macrocycle in the pseudorotaxane structure that rely mostly on O*H hydrogen bonds. Indeed, no strong base or polar solvent that could break up H-bonding can be used during the formation of rotaxanes because the two components will separate as two distinct entities. Moreover, most of the reactions have to be performed at room temperature to favor the formation of pseudorotaxane in solution. These non-trivial prerequisites have been taken into account to develop efficient reaction conditions for the preparation of rotaxanes and those are described in detail along this review.

Figure 1

Cartoon representation of a translational motion allowed in a [2]rotaxane.

Figure 2

Ammonium-crown ether-based rotaxane.

Scheme 1

Formation of a rotaxane by an esterification reaction.

Scheme 2

Formation of rotaxane via aminolysis of a prerotaxane.

Scheme 3

Formation of rotaxane via urethane formation.

Scheme 4

Formation of rotaxane via disulfide formation.

Scheme 5

Equilibrium process during the formation of [3]rotaxane through disulfide formation.

Scheme 6

Rotaxane formation through Wittig reaction.

Scheme 7

End-cap exchange through Tsuji-Trost allylation reaction.

Scheme 8

Rotaxane formation through metal-catalyzed hydrosilylation reaction.

Scheme 9

Rotaxane formation through ruthenium-catalyzed propargylic substitution.

Scheme 10

Rotaxane formation through ruthenium-catalyzed cross-metathesis.

Scheme 11

Rotaxane formation through Sonogashira coupling.

Scheme 12

Rotaxane formation through 1,3-dipolarcycloaddition.

Scheme 13

Rotaxane end-capping with C₆₀ through Diels-Alder reaction.

Scheme 14

Rotaxane formation through clipping of the macrocycle.

Scheme 15

Magic ring rotaxanes synthesis by ruthenium-catalyzed olefin metathesis.

Figure 3

Examples of rotaxane bearing amino acids moieties.

Scheme 16

Electrochemically-induced translational motion in rotaxane.

Figure 4

Supramolecular host for fullerenes based on rotaxane scaffold.