Polyester-Containing α‑Cyclodextrin-Based Polyrotaxane: Synthesis by Living Ring-Opening Polymerization, Polypseudorotaxanation, and End Capping Using Nitrile <i>N</i>‑Oxide

The first synthesis of polyrotaxanes consisting of polyester axles and α-cyclodextrin (α-CD) wheels was achieved by the catalyst-free click end-capping reaction of polypseudorotaxanes using nitrile <i>N</i>-oxide. The polypseudorotaxanes contain acrylate-functionalized polyesters that are obtained by the living ring-opening polymerization of lactones. The yield and coverage ratio of polyrotaxanes are highly dependent on the reaction time, molecular weight of the polyester, polyester structure, and solvent used. From the thermal properties of the resulting polyrotaxanes, it was found that coverage with α-CDs efficiently suppresses the crystallization of the polyester main chain

Click Annulation of Pseudo[2]rotaxane to [2]Catenane Exploiting Homoditopic Nitrile <i>N</i>‑Oxide

A mild annulation reaction of a propargyl-terminated pseudorotaxane with a homoditopic stable nitrile <i>N</i>-oxide enabled the efficient synthesis of catenanes consisting of not only dibenzo-24-crown-8-ether (DB24C8) but also dibenzo-30-crown-10-ether (DB30C10) as a wheel component. A dynamic ¹H NMR study showed the highly enhanced mobility of the components of the DB30C10-based [2]catenane due to the enlarged wheel cavity

Catalyst- and Solvent-Free Click Synthesis of Cyclodextrin-Based Polyrotaxanes Exploiting a Nitrile <i>N</i>-Oxide

A catalyst- and solvent-free synthesis of cyclodextrin-based polyrotaxanes exploiting a stable nitrile <i>N</i>-oxide as an end-capping agent was achieved. The C–C bond-forming end-capping reaction of an allyl-terminated pseudopolyrotaxane with the nitrile <i>N</i>-oxide proceeded smoothly by solid-state grinding in a mortar to afford a polyrotaxane

Intramolecular 1,3-Dipolar Cycloaddition of Nitrile <i>N</i>-Oxide Accompanied by Dearomatization

Intramolecular 1,3-dipolar cycloaddition of 2-phenoxybenzonitrile <i>N</i>-oxides to benzene rings, accompanied by dearomatization, formed the corresponding isoxazolines in high yields. The X-ray single-crystal structure analysis revealed that the reaction formed the <i>cis</i>-adduct as a single isomer. The substituents on the benzene rings markedly affected the reaction rate, yield, and structure of the final product

Synthesis of Highly Reactive Polymer Nitrile <i>N</i>‑Oxides for Effective Solvent-Free Grafting

A one-pot synthesis of polymer nitrile <i>N</i>-oxides was achieved via the Michael addition of living polymer anions derived from vinyl monomers to commercially available <i>trans</i>-β-nitrostyrene and subsequent dehydration with concd H₂SO₄. The polymer nitrile <i>N</i>-oxides are effective as grafting agents in catalyst- and solvent-free 1,3-dipolar cycloadditions to unsaturated-bond-containing polymers with high conversion and exhibit higher reactivity compared to that of nitrile <i>N</i>-oxides prepared from 1,1-diphenylnitroethene. Application to the preparation of a functional glass surface was demonstrated using P<i>t</i>BMA nitrile <i>N</i>-oxide as a grafting agent

Selective Synthesis of a [3]Rotaxane Consisting of Size-Complementary Components and Its Stepwise Deslippage

An α-cyclodextrin-based size-complementary [3]rotaxane with an alkylene axle was selectively synthesized in one pot via an end-capping reaction with 2-bromophenyl isocyanate in water. Thermal degradation of the [3]rotaxane product yielded not only the original components but also the [2]rotaxane. Thermodynamic studies suggested a stepwise deslippage process

Fluorescence Control of Boron Enaminoketonate Using a Rotaxane Shuttle

The effect of rotaxane shuttling on the fluorescence properties of a fluorophore was investigated by exploiting fluorophore-tethered [2]rotaxanes. A fluorescent boron enaminoketonate (BEK) moiety was introduced in a rotaxane via transformation of an isoxazole unit generated as a result of an end-capping reaction using a nitrile <i>N</i>-oxide. The rotaxane exhibited a red shift of the fluorescence maximum along with a remarkable enhancement of the fluorescence quantum yield through wheel translation to the fluorophore

Macromolecular [2]Rotaxanes: Effective Synthesis and Characterization

Macromolecular [2]­rotaxanes, which consist of a polymer chain threading into a wheel component, were synthesized in high yield and with high purity. The synthesis was achieved by the ring-opening polymerization (ROP) of δ-valerolactone (VL) using a hydroxyl-terminated pseudorotaxane as an initiator with diphenyl phosphate as a catalyst in dichloromethane at room temperature. The ¹H NMR, gel permeation chromatography (GPC), and MALDI-TOF-MS measurements of the resulting poly­(δ-valerolactone)­s clearly indicate the presence of the rotaxane structure with the polymer chain, confirming that the diphenyl phosphate-catalyzed ROP of VL proceeds without deslippage of the wheel component. The obtained macromolecular [2]­rotaxane was acetylated to afford a nonionic macromolecular [2]­rotaxane, in which only one wheel component is movable from one end to another along the polymer chain

Thermoresponsive Shuttling of Rotaxane Containing Trichloroacetate Ion

A thermoresponsive rotaxane shuttling system was developed with a trichloroacetate counteranion of an ammonium/crown ether-type rotaxane. Chemoselective thermal decomposition of the ammonium trichloroacetate moiety on the rotaxane yielded the corresponding nonionic rotaxane accompanied by a positional change of the crown ether on the axle. The rotaxane skeleton facilitated effective dissociation of the acid, markedly lowering the thermal decomposition temperature

Reversible Transformation of a One-Handed Helical Foldamer Utilizing a Planarity-Switchable Spacer and <i>C</i>₂‑Chiral Spirobifluorene Units

Polymeric quaterthiophenes containing optically active <i>C</i>₂-chiral spirobifluorene skeletons were synthesized as a new type of helical foldamers, and their higher-order structures were investigated. Oxidization of quaterthiophene moieties caused the spacer units to be in planar structure, leading the conformation of the polymer to be a coil-shaped, rigid helix. This transformation was reversibly performed