This review article describes supramolecular nanotubes formed by self-assembly of rationally-designed synthetic lipids or amphiphilic molecules in solvents. The nanotubes with functionalizable inner/outer surfaces and size-tunable diameters are able to encapsulate molecular medicine, biopolymers, and nanoparticles. In response to external stimuli such as pH, salt concentration, light, temperature, and moisture, the nanotubes release the guest compounds to bulk media. The stimuli responsive transformable nanotubes are also useful for conformational control of DNA and reaction control of enzymes.

Nanographenes, known as graphene quantum dots, are graphene fragments with a few to tens of nanometers. Due to the quantum size effect, nanographenes have bandgaps with a few eV and display photoemission in the visible region. These properties make nanographenes attractive research targets. Nanographenes can be obtained by the oxidative cleavage of parent carbons such as graphite and carbon fiber with strong oxidants. We have employed a mixture of concentrated sulfuric acid and 60% nitric acid as oxidants. Although as obtained products are the nonstoichiometric mixture of nanographenes, their size separation with dialysis membranes offers nanographenes with narrower lateral size distribution that displays excitation-wavelength-independent photoemission. Nanographenes carry a large number of carboxylic acid groups at the edge that can be utilized for chemical functionalization by organic synthesis. An example is the installation of 4-propargyloxy benzylamine at the edge. The reactive triple bonds on the resulting nanographenes allow to conduct the Cu(I) catalyzed click reactions, yielding edge-functionalized nanographenes. The click reaction of the nanographene with 1^st, 2^nd, and 3^rd generation dendritic wedges produces white-light-emitting nanographenes and the installation of both long alkyl chains and ureidopyrimidinone groups, which form self-complementary four-fold hydrogen bonds, into the edge drives the self-assembly of the functionalized nanographenes to organize polymer-like structures that function as organogelators. This article focuses on the chemical modification of nanographenes by organic synthesis.

Oxidation of aryl amines has been extensively utilized for the synthesis of nitrogen-containing functional materials. Among them, a number of methods for C-C bond forming reaction of aryl amines have been developed. Although oxidative biaryl coupling of aryl amines using stoichiometric metal or organic oxidants has been reported, the catalytic oxidation methods have been rarely studied to date. The aerobic oxidation is an attractive approach toward environmentally friendly synthesis of nitrogen-containing biaryl compounds. Recently, we developed a heterogeneous rhodium-catalyzed aerobic oxidative biaryl coupling reaction of aryl amines to provide various aminobiaryls such as BINAM derivatives, naphthidines, benzidines, and bicarbazoles. This heterogeneously catalyzed method can be adapted to highly selective cross-coupling reaction and the intramolecular biaryl coupling reaction of aryl amines. Additionally, we developed an aerobic direct C-H oxidation of polycyclic aromatics using a recyclable heterogeneous catalyst. In this account, our recent research activities regarding the heterogeneously catalyzed aerobic oxidative transformations of aromatic C-H bonds are described.

In recent years, hypervalent iodine reagents have gained increasing popularity in metal-free oxidative transformation due to their low toxicity, easy handling, transition-metal-like reactivity, and other benefits. However, although metal-free oxidative transformations of alkynes using iodine (III) reagents have been well studied for the preparation of alkynyl (aryl) iodonium and alkenyl (aryl) iodonium salts, stepwise methods including preparation step of these iodonium species have been commonly used in the synthesis of heterocycles from alkynes. In this account, our two approaches to the metal-free and single-step synthesis of heterocycles via an activation of alkynes by iodine (III) are mainly described. One is iodine (III)-mediated/catalyzed oxidative cycloisomerization reactions of propargyl compounds for the preparation of heterocycles bearing various functional group at their side chains. In these reactions, iodine (III) species works as an activator of carbon-carbon triple bonds as well as a donor of various heteroatomic functional groups. This methodology can be extended to iodine (III)-mediated/catalyzed oxidative annulation of alkynes and nitriles as another approach, in which heteroatoms on iodine (III) species are incorporated in the azole rings. In addition, molecular iodine-catalyzed cyclization of o-alkylanilines via iodocyclization/proto-deiodination sequence is described as an iodine catalysis without terminal oxidants.

Cyclopropanes serve as valuable building blocks in organic synthesis because of their high reactivity based on their strong ring strain. On the other hand, spirocyclopropanes have rarely been utilized in synthetic organic chemistry despite their high potential because of their low availability. Since we reported an efficient preparation method of cyclohexane-1,3-dione-2-spirocyclopropane and its ring-opening cyclization with amine to form a bicyclic compound, tetrahydroindol-4(5H)-one, we have investigated reactions of spirocyclopropanes with various nucleophiles to provide the bicyclic heterocycles. In this account, we have summarized our research on the development of the reactions using unique nucleophiles possessing a leaving group moiety. Ring-opening cyclization of spirocyclopropanes with a catalytic amount of iodide, which acts as both a nucleophile and a leaving group, regioselectively produced 2- or 3-substituted tetrahydrobenzofuran-4-ones in high yields. In addition, stabilized sulfonium ylides and sulfoxonium ylides were used for the ring-opening cyclization of spirocyclopropanes and constructed chromane skeletons. We also show the utility of the ring-opening cyclization products, tetrahydroindol-4(5H)-ones, as key intermediates for synthesis of highly substituted indoles and Aspidosperma alkaloids. Moreover, we demonstrated the synthesis of 1-azaazulenes employing ring-opening cyclization of cycloheptane-1,3-dione-2-spirocyclopropane with 2,4-dimethoxybenzylamine.

Bismuth (₈₃Bi), the heaviest stable metal element, has recently gained much attention as novel redox catalysts. The unique redox properties of bismuth could provide an opportunity to develop alternatives to transition metal catalysts using the low-cost and green metal. This review highlights some magnificent recent works that demonstrated the potential of bismuth catalysts in cross-coupling, one-electron oxidation, and small-molecule activation reactions.

Amides and esters are ubiquitous substructures in life sciences, pharmaceuticals, and bioactive natural products. Although numerous coupling reagents for amidation and esterification have been developed to date, synthetic methodology avoiding poor atom economy and E-factor is still required. Recently, several groups have reported utility for the heteroatom-substituted terminal alkynes as coupling reagents, which react with carboxylic acids in a “click” manner. In this mini review, recent reports about atom-economic amide and ester synthesis via activated vinyl esters are highlighted.