Applicability and productivity of new click chemistry that exploits a nitrile N-oxide as a 1,3-dipole in polymer synthesis were demonstrated by the polymerization of diynes with a homo ditopic aromatic nitrile N-oxide. The nitrile N-oxide was synthesized in situ by the reaction of the corresponding hydroxamoyl chloride with molecular sieves 4 Å. The click polymerization of various ditopic diynes and the nitrile N-oxide efficiently produced polyisoxazoles in high yields. The homo ditopic nitrile N-oxide was also useful for the connection of bisacetylene-terminated polymers to give multiblock copolymers in very high yield. The resulting polyisoxazoles agree well with the structural assignment obtained by the 1H and 13C NMR analyses. The generated polyisoxazoles showed improved thermal stability due to the presence of isoxazole moieties. The molecular diversity of the obtained polyisoxazoles was confirmed by the selective transformations of the isoxazole moieties into β-aminoenone or β-aminoalcohol moieties with high conversion rates. The thermal decomposition temperature of the transformed polymers was lower than that of the polyisoxazoles because of the formations of abundant amino and hydroxyl groups. Furthermore, the functionality of poly(β-aminoalcohol) was proven by quantitatively cross-linking the polymers by treatment with terephthalaldehyde or methylene diphenyl diisocyanate.

We developed a one-pot synthetic technique for alternating peptides. Central to this technique is a new, catalyst-free polymerization based on Ugi's 4CC reaction. The treatment of imines with the ambident molecules bearing both an isocyanide and a carboxylic acid afforded alternating peptides.

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 δvalerolactone (VL) using a hydroxyl-terminated pseudorotaxane as an initiator with diphenyl phosphate as a catalyst in dichloromethane at room temperature. The 1 H 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 phosphatecatalyzed 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.

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Break it down: Gels formed from rotaxane cross‐linkers with end groups that are size‐complementary to the macrocyclic cavity of wheel components (see picture) were prepared. The network structure was maintained in polar organic solvents or in the presence of a base to prevent hydrogen bonding. Anion exchange enabled the selective and efficient de‐cross‐linking of the gels.

Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotaxanes that consisted of optically active crown ethers and sec-ammonium salts with an ethynyl benzoic acid. The monomers were polymerized with [{RhCl(nbd)}(2)] (nbd=norbornadiene) to give the corresponding polyacetylenes in high yields. Polymers with optically active wheel components that are far from the main chain show no Cotton effect, thereby indicating the formation of racemic helices. Our proposal that N-acylative neutralization of the sec-ammonium moieties of the side-chain rotaxane moieties enables asymmetric induction of a one-handed helix as the wheel components approach the main chain is strongly supported by observation of the Cotton effect around the main-chain absorption region. A polyacetylene with a side-chain rotaxane that has a shorter axle component shows a Cotton effect despite the ammonium structure of the side-chain rotaxane moiety, thereby suggesting the importance of proximity between the wheel and the main chain for the formation of a one-handed helix. Through-space chirality induction in the present systems proved to be as powerful as through-bond chirality induction for formation of a one-handed helix, as demonstrated in an experiment using non-rotaxane-based polyacetylene that had an optically active binaphthyl group. The present protocol for controlling the helical structure of polyacetylene therefore provides the basis for the rational design of one-handed helical polyacetylenes.

New click chemistry is demonstrated. Click polymerization proceeded via 1,3-dipolar polycycloaddition of homo-ditopic nitrile oxides to bifunctional terminal olefinic and acetylenic monomers as dipolarophiles. Molecular sieves (MS 4A) served as an efficient promoter for the polymerization to afford polyisoxazolines and polyisoxazoles in high yields.

A click end-capping reaction exploiting nitrile N-oxide to rotaxane was described with emphasis of productivity of the protocol via stable C-C bond formation. Establishment of a pH-driven molecular shuttling system was also demonstrated by practical neutralization of the sec-ammonium group of the rotaxane axle with potassium hydroxide.