In 2008, while investigating an indium-catalyzed reaction, we encountered an experimental result serendipitously, which led to the development of the reaction that became the main subject of this account article. The finding eventually evolved into the discovery of the zinc/pyridine-catalyzed dehydrogenative N-silylation of indoles in a nitrile medium. The zinc/pyridine/nitrile system proved remarkably versatile, being applicable not only to the dehydrogenative C-silylation of indoles, but also to the dehydrogenative silylation, stannylation, and borylation of alkynes. This system is attractive in practice because all the catalyst, additive, and solvent are commercially available and thus executed in an easy manner. In addition, excellent functional-group tolerance with broad substrate scope and consistently high yields of products make this system valuable and reliable. Alkynyl-B(dan), derived from the dehydogenative borylation of alkynes, serves as a valuable platform for the synthesis of unsymmetrical tetrasubstituted alkenes. Moreover, we first achieved the Suzuki-Miyaura coupling (SMC) of alkynyl-B(dan) through the direct activation of the C-B(dan) bond, which has hitherto been recognized as highly robust and inert. Taking advantage of the insights, we further accomplished the first direct SMC of ArB(dan).

Perfluorinated polymer electrolyte membranes (PEMs), prepared from copolymers of tetrafluoroethy-lene and perfluorinated sulfonyl fluoride monomers (SO₂F monomers), CF₂＝CF[OCF₂CF(CF₃)]_mO-(CF₂)_nSO₂F, have been employed in chlor-alkali process, polymer electrolyte fuel cell, and polymer electrolyte water electrolysis. Compared to long-side-chain (LSC) PEMs, short-side-chain (SSC) PEMs have shorter side chains, resulting in higher glass transition temperature, lower equivalent weight, and higher ionic conductivity. However, SSC-SO₂F monomers (m＝0, n＝2 or 4) cannot be synthesized in the same way as LSC-SO₂F monomer (m＝1, n＝2). Therefore, they are synthesized using special reaction reagents and equipment. We have developed novel synthetic methods for SSC-SO₂F monomers with different side-chain lengths using commercially available reagents. Two synthetic methods for SSC-SO₂F monomer (m＝0, n＝2) were developed using CF₃CF(COF)O-(CF₂)₂SO₂F, a synthetic intermediate of LSC-SO₂F monomer (m＝1, n＝2), as the starting material. One method used imidazole as the protecting group and the other used cyclic compound and vinyl sulfonic anhydride. Additionally, we investigated two synthetic routes for SSC-SO₂F monomer (m＝0, n＝4) using the same commercially available reagents, but in different order of use, starting with I(CF₂)₄I. As a result, we chose the route of first synthesizing the sulfonyl fluoride group, followed by the vinyl ether group.

[n]Cycloparaphenylenes (CPPs), a distinctive family of π-conjugated nanohoops, have attracted great interest owing to their highly strained cyclic structures and unique photophysical and electrochemical properties. For a long time, [n]CPPs were considered “dream molecules” due to the difficulty of bending benzene rings into cyclic architectures. However, between 2008 and 2010, independent breakthroughs by several research groups finally realized their synthesis, and since then a wide variety of [n]CPPs and derivatives have been reported. We have recently established an innovative approach to CPPs and related nanohoops utilizing macrocyclic gold complexes as key intermediates. This gold-mediated strategy offers unique advantages: (i) efficient access to [n]CPPs with ring sizes that are multiples of three; (ii) the recyclability of the digold complex; enabling cost-effective and environment-friendly synthesis; (iii) the use of readily available arylboronic acids as starting material; (iv) the ability to introduce bulky substituents owing to the open coordination environment of Au(I) -diphosphine unit; (v) incorporation of coordinating units such as bipyridines; and (vi) mild reaction conditions that tolerate chemically sensitive substituents. Importantly, the discovery of dynamic Au-C σ-bond exchange provided mechanistic insight into the high cyclization efficiency, enabling the development of a “reorganization method,” in which two different macrocyclic gold complexes can be mixed and subsequently reductively eliminated to construct nanohoops incorporating two distinct organic linkers. Collectively, these results highlight the versatility of gold-mediated CPP synthesis as a powerful platform for constructing structurally diverse and functionalized π-conjugated macrocycles.

Spiro π-conjugated compounds, consisting of two orthogonally arranged π-conjugated frameworks, exhibit unique optical and electronic properties, along with high solubility and thermal stability. Owing to these features, they have been extensively studied as fundamental scaffolds for functional organic materials. Depending on the substitution pattern, spiro π-conjugated compounds can also be chiral, and various chiral spiro π-conjugated compounds have been synthesized to date. However, studies focusing on their chirality remain rather limited. Recently, our group has developed a series of chiral spiro π-conjugated compounds, in which heteroles and/or donor-acceptor structures are incorporated to tune the optical properties. This article describes the synthesis of these chiral spiro π-conjugated compounds and the elucidation of their optical properties, including circularly polarized luminescence (CPL) characteristics. These systematic studies provide new insights into the structure-property relationships of chiral spiro π-conjugated compounds.

In recent years, chiral dyes capable of showing circularly polarized luminescence (CPL) have received considerable attention due to their potential applications to 3D displays, security paints, information storages, and bioimaging. CPL was usually evaluated by a dissymmetry factor, g_lum, and chiral dyes showing high g_lum values have been developed. Attachment of chromophores to a chiral platform is one of the convenient methods to prepare chiral dyes, and pyrenes, BODIPYs, and porphyrins linked with axially chiral binaphthyls and cyclodextrins showed CPL in the region of the chromophores. On the other hand, helicenes, ortho-fused aromatics, show intense CPL originating from the inherent chirality. We developed boron dyes with carbazole-1,3-azole ligands showing solid-state fluorescence, and later we found the Et₂AlCl-mediated reaction to give chiral boron dyes with (R)- or (S)-BINOL showing CPL both in solution and solid states. We also developed azahelicene-fused boron dyes, whose azahelicene framework was newly synthesized via the intramolecular oxidative coupling of 3,6-bis(biphenyl-2-yl)carbazole. The short-step synthesis of the azahelicene allowed for the preparation of a variety of derivatives including cyclic azahelicene dimers, π-extended helicenes, and multiple helicenes. Here the synthesis and chiroptical properties of these chiral boron complexes and azahelicenes.