Plastics are indispensable material that supports our daily life. The amounts of their production and waste are increasing in every year, and their recycling is recognized as a key issue for sustainable development of the world. Plastics are carbon resources and should be recycled in a proper manner. Chemical recycling is a concept in which plastics are treated chemically to give monomer or related compounds that would serve further use. Although chemical recycling of plastics is an ideal way, it is still difficult to carry it out. In this account, we focus on the depolymerization reaction of several plastics, and show how basic knowledge and recent development of synthetic organic chemistry provide important idea and solution on this matter. Use of supercritical alcohols and ionic liquids offered new and valuable methods. We applied the methodology developed here to biomass conversion, and we show the results about this application.

Vinyl triflates are valuable precursors for vinyl cations, vinyl carbenes, and electrophiles for transition-metal-catalyzed cross-coupling reactions. However, in these reactions, the trifluoromethyl group is not installed in the final products. The radical reactions of vinyl triflates were limited until our beginning. We initially achieved the synthesis of α-trifluoromethylated ketones from vinyl triflates using triethyl borane as a radical initiator. Since the reaction proceeds chemoselectivity toward the conjugated vinyl triflates, we achieved the chemo- and regio-selective trifluoromethylation of 1,3-bis(vinyl triflates). We developed one-pot trifluoromethylation from aryl alkynes with perfluoroalkanesulfonic acids in the presence of AIBN as a radical initiator. In addition, a crossover experiment and DFT calculations support that the reaction proceeds through an intermolecular pathway. The radical reaction of vinyl triflates in the presence of alkenes afforded γ-trifluoromethylated ketones. We also developed a one-pot triflation-trifluoromethylation-triflation of imines leading trifluoromethyl-substituted vinyl trifluoromethanesulfonic amides.

Glaziovianin A is an isoflavone derivative isolated from the leaves of Brazilian tree. Glaziovianin A shows antitumor activity and inhibition of α,β-tubulin polymerization. We developed gatastatin, which was O⁷-benzyl glaziovianin A, as a specific inhibitor of γ-tubulin. To the best of our knowledge, gatastatin is the first γ-tubulin-specific inhibitor. Because gatastatin specifically inhibits γ-tubulin, we synthesized O⁶-modified gatastatin for the development of γ-tubulin-specific inhibitor by using oxidative removal of methyl ether group in aromatic ring, as a key step. As results, O⁶-propargyl gatastatin showed strong inhibitory activity against γ-tubulin. We named this compound as “gatastatin G2”. The inhibitory activity against γ-tubulin of gatastatin G2 was stronger than that of gatastatin. This compound would be a useful tool for investigating γ-tubulin function in cells.

Introduction of various types of substituents onto oligosilane chains is important for not only synthesis scheme of functionalized oligosilanes but also modification and tuning of the unique photophysical and electronic properties. To explore further potentials of oligosilanes, development of their synthetic methods is essential. Since transition metal-based methodologies have contributed greatly to the remarkable progress in synthetic organic chemistry, application of similar strategies for the oligosilane synthesis is highly desirable. However, few such attempts have been reported so far, probably due to the intrinsic reactivity of the Si-Si bond toward transition metal species. We are trying to develop the transition metal-catalyzed reactions of oligosilanes without Si-Si bond cleavage. In this paper, titanium-catalyzed selective monoreduction of dichlorooligosilanes, ruthenium-catalyzed alkoxylation of hydrooligosilanes, and ruthenium-catalyzed regio- and stereoselective hydrosilylation reactions using hydrooligosilanes are described. By choosing appropriate catalysts, these reactions successfully provide a series of novel oligosilane derivatives with the Si-Si bond intact.

In recent years, functional molecules involving expanded π-conjugation circuits have attracted attention owing to their merits to construct optoelectronic materials such as photovoltaic cells. Among functional molecules bearing expanded π-conjugation circuits, porphyrin derivatives having ring-fused structures at the periphery have attracted attention as reflected on the fact that a lot of the new derivatives have been synthesized in this decade to develop their unique optoelectronic characteristics. For instance, ring-fused porphyrins exhibit near IR absorption bands due to small HOMO-LUMO gaps derived from the expanded π-conjugation. This manuscript briefly surveys the syntheses and properties of the ring-fused porphyrin derivatives reported since 2010.

Dehydrogenative silylation, which produces vinyl silanes, was generally regarded as a side reaction in hydrosilylation of alkenes. However, due to a utility of vinyl silanes, transition-metal catalyzed dehydrogenative silylations have been developed. This mini-review focuses on recent developments of manganese-catalyzed selective dehydrogenative silylation of alkenes.