Published papers

A catalyst-dependent chemoselective photoredox reaction of cyanopyridines and cyanoarenes with N-aryl tertiary amines is described. In competitive reactions under visible-light irradiation, a conventional iridium photocatalyst preferentially promoted coupling of the cyanoarene component, whereas phenothiazine-based catalyst systems, including a DATB–phenothiazine hybrid, favored formation of cyanopyridine-derived products. The cyanopyridine-selective product distribution was observed across several combinations of amines, cyanopyridines, and competing cyanoarenes. These results show that the identity of the photocatalyst can govern the relative substrate preference of closely related cyano(hetero)arene acceptors in photoredox catalysis.

Systematic comparison of hydroxy-, amino-, amide-, sulfonamide-, and phosphinamide-substituted C4N4 fluorophores revealed that fluorescence is modulated not simply by hydrogen-bond donor strength, but by positional, geometrical, and conformational accessibility of intramolecular hydrogen bonding to the pyrimidine core. This insight was translated into an acetylation-responsive turn-on probe, providing a design basis for responsive C4N4 fluorophores.

Catalyst-controlled vinylogous aza-MBH reactions of vinylcyclopentenone were performed, and it was found that the α-adducts were exclusively obtained by DABCO-catalysis, while the γ-adducts were the major products by DMAP-catalysis. We report here that the rate-determining step of the DABCO-catalyzed α-selective reactions is the Mannich-type C−C bond forming step, while that of the DMAP-catalyzed γ-selective reactions seems to be the β-elimination step.

The C4N4 fluorophore is an intense fluorescence emitter featuring a 2,5-diaminopyrimidine core comprising four carbon and four nitrogen atoms. A series of C4N4 derivatives was photochemically dimerized at the 5-amino group, furnishing overcrowded ortho-tetraaryl-substituted diaryl azo compounds with a characteristic skewed structure revealed by X-ray crystallography. The photoquenched azo-C4N4s are useful for fluorescently visualizing cells under hypoxic conditions.

DATB (1,3-dioxa-5-aza-2,4,6-triborinane) is a unique six-membered heterocycle exhibiting proficient catalytic activity in direct dehydrative amidation. Reported herein is an improved synthetic protocol for DATB derivatives featuring a concise two-step chromatography-free process. Suzuki-Miyaura coupling assembled 2,6-dibromoaniline derivatives and 1,2-phenylenediboronic acid to afford dimeric B-spiroborate salts. Acidic untying of the spiroborates gave rise to the DATB ring system with various substituents.

We report a new class of nitrogen-containing π-extended heterocycles, DiazaChrysenes (DCs), and their dimeric analogues (dDCs) as metal-free photocatalysts for C–H amination. DCs featuring a quinolino[1,2-c]quinazolin-5-ium core were synthesized via electrophilic amide activation and arylation. The resulting compounds displayed tunable photophysical and redox properties, with CF3-substituted DCs enabling the C–H amination of arenes with azoles under visible light and aerobic conditions, achieving yields up to 85%. The reaction tolerated a range of arene and azole substrates without requiring metal salts or additives. In contrast, dDCs exhibited diminished activity, likely due to their extended π-curvature. Computational studies, including NCI, ACID, and NICS analyses, revealed locally aromatic but electronically isolated π-systems and deshielded central 8-membered cores. This work highlights the utility of DC scaffolds as synthetically accessible and redox-tunable organic photocatalysts.

TriQuinoline (TQ), a quasi-planar cyclic quinoline trimer concatenated at the 2,8-positions in a head-to-tail arrangement, strongly captures a proton at the 12-membered inner cycle and exhibits unusual physicochemical properties, including unexpected water solubility and the ability to engage in complexation with other π-conjugated molecules. In this study, we designed and synthesized its expanded analog, coined Enlarged-TriQuinoline (Enl-TQ), in which three alkyne units are embedded between three quinoline units to acquire an expanded planar 18-membered ring system. DFT calculations and X-ray crystallographic analysis revealed its planar architecture with three inwardly facing pyridinic nitrogen atoms. Despite its structural similarity to TQ, Enl-TQ displayed distinct host capability and photophysical characteristics.

Heteroatom-doped graphitic materials, particularly those bearing nitrogen, have attracted considerable attention because of their unique physicochemical properties, which are unattainable in pristine carbon frameworks. To rigorously investigate the effects of doping and to enable fine-tuning of their functions at the atomic scale, bottom-up synthesis of well-defined molecular surrogates provides a powerful approach. Herein, we report the design, synthesis, and physicochemical characterization of a series of quinoline/quinazoline cyclic trimers, TriQuinoline (TQ, Q3), Q2Qz1, Q1Qz2, and TriQuinazoline (TQz, Qz3), featuring an atomic-sized central cavity surrounded by three pyridinic nitrogens that mirrors the local topology of nitrogen-doped graphene defects. A modular synthetic strategy enabled facile access to all of the quinazoline-containing congeners. Systematic X-ray analysis and computational studies revealed increasing molecular planarity with increasing quinazoline incorporation, arising from stepwise elimination of destabilizing CH···HC contacts and the emergence of favorable CH···N interactions. Spectroscopic and theoretical studies demonstrated that quinazoline substitution progressively decreases the proton affinity at the central cavity owing to the electron-withdrawing nature of the quinazoline units, which markedly accelerates proton exchange. Even with these electronic modifications, supramolecular association with polycyclic aromatics, such as coronene and [12]cycloparaphenylene ([12]CPP), substantially remained preserved upon quinazoline incorporation. These findings highlight the cooperative interplay of structural planarity and heteroatom substitution in dictating the properties of discotic heteroaromatics, offering a versatile platform for material design.

Metal fluorides such as KF and CsF are inexpensive and easy-to-handle nucleophilic fluorinating reagents while their insolubility in most organic solvents often causes a problem in their synthetic use. In this review, examples of nucleophilic fluorination promoted by a hydrogen-bonding donor are described. Moreover, a recent research on asymmetric nucleophilic fluorination using a chiral hydrogen-bond donor catalyst is introduced.

Ruthenium-catalyzed hydrogen transfer from 4-aminobutanol to butadiene results in the pairwise generation of 3,4-dihydro-2H-pyrrole and an allylruthenium complex, which combine to form products of imine anti-crotylation. In couplings of 1-substituted-1,3-dienes, novel C2 regioselectivity is observed. As corroborated by deuterium labeling studies, kinetically preferred hydrometalation of the terminal olefin of the 1-substituted-1,3-diene delivers a 1,1-disubstituted π-allylruthenium complex that isomerizes to a thermodynamically more stable monosubstituted π-allylruthenium complex, which undergoes imine addition with allylic inversion through a closed transition structure. Direct ruthenium-catalyzed diene hydroaminoalkylations with pyrrolidine also are described.

A novel class of chiral N-sulfonyl oxaziridines is catalytically prepared and introduced for use as highly reactive and enantiospecific oxidants.

Chiral beta-ketonitriles bearing a stereogenic carbon center at the alpha-position are an important class of compounds, many of which serve as useful synthetic intermediates for the preparation of chiral 1,3-aminoalcohols, beta-hydroxy nitriles, and related derivatives. Although the enantioselective electrophilic cyanation of enolate equivalents is one of the most promising approaches for the synthesis of chiral beta-ketonitriles, the available methods are largely limited to reactions of 1,3-dicarbonyl compounds. Herein, we report on enantioselective electrophilic cyanation of boron enolates, which are readily prepared from alpha,beta-unsaturated ketones and diisopinocampheylborane (Ipc(2)BH) to afford chiral beta-ketonitriles with a high level of enantioselectivity. The present method is scalable and provides facile access to both enantiomers of chiral beta-ketonitriles. Analysis of the in situ generated boron enolates by NMR revealed that hydroboration proceeds in a stereospecific manner, providing alpha,alpha-disubstituted boron enolates in the form of single isomers. Furthermore, the results of DFT calculations suggest that the cyanation of the boron enolates with p-toluenesulfonyl cyanide (TsCN) proceeds in a highly enantioselective manner through a unique six-membered ring transition state.

Aryllithiums were arylated with S-arylphenothiazinium ions through selective ligand coupling of intermediary sulfuranes. Various unsymmetrical biaryls were obtained without transition-metal catalysis.

渦鞭毛藻Karenia brevisより単離された天然物ブレビシンのABC環部分の合成を行った。