Preparation of Pillar[5]arene‐Based [2]Rotaxanes from Acyl Chlorides and Amines (Eur. J. Org. Chem. 3/2015)

Abstract

The cover picture shows a pseudorotaxane intermediate bearing an acyl chloride unit ready to react with an amine stopper to afford a pillar[5]arene‐based [2]rotaxane. The yield of [2]rotaxane is sensitive to the reaction conditions but also to electronic and structural factors, in particular the nature of the amine reagent and the size of the peripheral groups on both rims of the pillar[5]arene building block. Details are discussed in the article by R. Deschenaux, J.‐F. Nierengarten et al. on .

A Rotaxane Scaffold for the Construction of Multiporphyrinic Light‐Harvesting Devices

“…Finally,t reatment of 7 with KOH in H 2 O/THF provided alcohol 8.T he preparation of a model [2]rotaxane was then attempted by reactiono f8 with acyl chloride 10 in the presence of pillar[5]arene 9.I no rder to obtain the desired [2]rotaxane in good yields, the reaction conditions must favor the assembly of ap seudo-rotaxane intermediate from 8 and 9.F or this reason, the reaction was carried out at À15 8Ca nd at the highest possible concentration. [14] Moreover,p illar[5]arene 9 was also used in excess (2 equiv.). It can be also noted that the choice of CHCl 3 as solvent is critical to obtain the desired [2]rotaxanei ng ood yields.…”

“…Indeed, this solventi su nable to form inclusion complexes with macrocycle 9 and there is no competition for the binding of guest 8. [13,14] Under thesec onditions, [2]rotaxane 11 was obtained in ar emarkable 77 %y ield. Axle 12 was also formed and this byproduct was isolated in 3% yield.…”

“…Actually,i th as been already shown that the size of the peripheral groups on both rims of the pillar[5]arene building blocks are affecting the outcomeo fs uch reactions. [14] When their size is increased, the reaction of the pseudo-rotaxane intermediate is slowerd ue to steric effects and the unthreaded axle is consumedf aster. As ar esult,t he equilibrium is progressively displacedi nf avor of the unthreaded intermediate thus contributing to increase the yield in dumbbell while lowering the yield in [2]rotaxane.…”

“…The combinationo f1 with an appropriate energy acceptor,n amely af ree-base porphyrin subunit, [10] has been conveniently achieved by taking advantage of the capability of the pillar[5]arene core to form inclusion complexes allowing for the preparation of [2]rotaxanes. [11][12][13][14] The synthesis of compound 2 has been efficiently achieved and steady-state measurements revealed that the light energy absorbed by its peripheralZ n-porphyrin moieties is effectively channeled to the free base porphyrin stopper.D etailed electrochemical investigations of compound 2 revealed also ap eculiar behaviorr esulting from the intramolecular coordination of the Zn(II) porphyrin moieties to 1,2,3-triazole units.…”

Regulation of Macrocycle Shuttling Rates in [2]Rotaxanes by Amino‐Acid Speed Bumps in Organic–Aqueous Solvent Mixtures

“…[1] Indeed a variety of effective methods for the synthesis of rotaxanes has been established through numerous synthetic strategies. [2][3][4][5] Among a wide diversity of reported interlocked structures, molecular shuttles comprising a mobile macrocycle threaded on a two-station axle, is one of the most emblematic types of architecture, which serves as an excellent platform for bottom-up studies of dynamic properties. [6][7][8] With sub-molecular movement being integral to potential function in molecular machines, regulation of dynamics, both spontaneous and stimulus-induced, is essential and intimately linked with molecular design.…”