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.

Quinoline-based aromatic oligoamide foldamers composed of anilide (A) and quinoline (Q) units, in which amide-bond formation at the quinoline 8-position provides access to cyclic and acyclic architectures, exhibit distinct folding behaviors. The cyclic series A(n)Q(n) (n = 2–6) was obtained by one-pot cyclooligomerization or by stepwise assembly followed by intramolecular amidation. Structural analyses revealed a pronounced ring-size dependence of conformation and symmetry, ranging from symmetric macrocycles to unsymmetric, partially helical folds. In particular, the hexamer A6Q6 exhibits an unusual two-state conformational equilibrium in solution and was isolated in the solid state as both a partially helical unsymmetric conformer and a highly symmetric S6 cubic conformer featuring a hydrophobic internal cavity. In parallel, the corresponding acyclic oligomers NH2-A(n)Q(n)-CO2H (n = 3–6) adopt well-defined helical structures in the solid state and retain compact folded conformations in solution, as supported by NMR, H/D-exchange, and NOE analyses. The helical fold generates a confined cavity comparable in size to that of a 12-membered ring. These findings establish anilide–quinoline hybrids as a versatile platform for size-programmed macrocycles, stable aromatic helices, and functional foldamer architectures.

Macrocyclic compounds, exhibiting unique properties arising from their large-ring frameworks, have captivated the attention of organic chemists over the last few decades. These molecules serve specific functions across disciplines, including synthetic chemistry, materials science, and biology. Representative molecules in this category, including crown ethers, calix[n]arenes, and porphyrinoids composed of ether/phenol/pyrrole subunits, exhibit unparalleled structural and functional diversity. In contrast, macrocycles exploiting quinoline/quinazoline as key building blocks to construct specific macrocyclic architectures have received limited attention and are much less explored. In this Highlight Review, we summarize our recent advances in oligo-quinoline/quinazoline macrocycles. Emphasis is focused on synthetic strategies, structural features, and emerging applications in organometallic, supramolecular, and photophysical chemistry. We anticipate that these collective results will guide new molecular designs within the broader family of heterocycle-based macrocycles.

Compact organic fluorophores are attractive scaffolds for probe design, yet their emission is often compromised by efficient nonradiative decay. Here, we introduce 2,5-diaminopyrimidine-based C4N4 as an intrinsically emissive, exceptionally small platform, which remains bright without extended π-conjugation. Systematic substitution at 4,6-positions with alkyl, alkenyl, and alkynyl groups reveals robust emission for alkyl and alkynyl derivatives, and a striking bimodality for alkenyls. TDDFT combined with ES/SC-AFIR mapped the S1→S0 internal-conversion landscape, providing a rationale for substituent-dependent relaxation behavior. Manipulation at the 5-position allowed for independent trigger-responsive emission behavior. This orthogonal design, where the 4,6-substituted C4N4 core serves as the fluorophore and the 5-position operates as ON/OFF gate, enabled the development of turn-on probes for Pd2+.

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.

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.

Chiral macrocycles are attracting growing interest due to their broad applicability as ligands in asymmetric catalysis and as host molecules for chiral recognition. Robustness and high thermodynamic stability can be effectively achieved by strategically linking aromatic panels to construct an axially chiral macrocyclic framework. Cyclic concatenation of four quinoline units affords a fully sp2-hybridized, non-planar macrocycle featuring four inwardly oriented, coordinatively active pyridyl nitrogen atoms. The previously reported tetramer TEtraQuinoline (TEQ) exhibits head-to-tail connectivity of its quinoline units, affording an achiral architecture possessing S4 symmetry. Herein, we report the design and synthesis of iso-TEtraQuinoline (i-TEQ), an inherently chiral analogue featuring head-to-head connectivity at the 2,2′- and 8,8′-positions, which gives rise to a D2-symmetric architecture. Detailed comparative investigations of the connectivity isomers i-TEQ and TEQ revealed an array of distinct characteristics, including the overall architecture, intrinsic macrocyclic strain, spatial orientation of nitrogen lone pairs, thermodynamic stability, racemisation behaviour, metal complex stability, and circularly polarised luminescence.

A chemoselective dehydrogenation protocol for benzylic amines catalyzed by the TEtraQuinoline (TEQ)/FeCl2 complex is described. In combination with 2 equiv of tert-butyl hydroperoxide, as little as 0.1 mol% of catalyst loading was sufficient to convert primary and secondary benzylic amines to the corresponding imines and dimerized imines, respectively. Subsequent hydrolysis of the imines allowed for removal of the benzyl group on the nitrogen atom. Nonaromatic carbon-carbon multiple bonds and the O-Bn group remained intact in the present protocol, providing a complementary deprotection procedure to reductive removal conditions exerted by Pd catalysis.

A new family of 16-membered macrocycles comprising two indole (In) and two quinoline (Q) units, coined In2Q2, was synthesized. Each unit is diagonally located and concatenated in a head-to-tail fashion, furnishing a non-flat saddle-shaped architecture with C2 symmetry. The synthetic protocol utilizing macrocyclic diamide as a pivotal precursor allowed us to access a series of In2Q2 derivatives bearing various substituents on the periphery. The In2Q2 derivatives and their Zn2+ complexes were emissive in both solution phase and solid state. While the entire architecture of In2Q2 is similar to that of quinoline tetramer TEtraQuinoline, a couple of contrasting physicochemical properties were revealed.

Macrocyclic compounds exhibit unique properties due to their large ring-shaped structures, which have captivated chemists in recent decades. These molecules exert specific functions in various applicable fields, such as chemistry, materials science, and biology. Crown ethers, calixarenes, and porphyrinoids, which contain several ether/phenol/pyrrole subunits, represent these molecular categories with unparalleled functional diversity. In contrast, quinoline-based macrocycles comprising the quinoline unit as a key element to construct specific ring shapes have received limited attention. In this minireview, we summarize the recent advances in oligoquinoline macrocycles TriQuinoline (TQ), oxa-TriQuinoline (o-TQ), TEtraQuinoline (TEQ), and other bridged quinoline-based macrocycles. Emphasis is placed on the synthesis, structure, and application of these molecules in organometallic and supramolecular chemistry, which may guide new molecular designs in the quinoline-based macrocycle family. 1 Introduction 2 Quinoline-Based Macrocycles 2.1 TriQuinoline (TQ) 2.2 Oxa-TriQuinoline (o-TQ) 2.3 TEtraQuinoline (TEQ) 2.4 Larger Quinoline-Based Macrocycles with Bridges 3 Conclusion.

Macrocyclic compounds exhibit unique properties due to their large ring─shaped structures, which have captivated chemists in recent decades. These molecules exert specific functions in a multidisciplinary basis, e.g. chemistry, materials science, and biology. Crown ethers, calix [n] arenes, and porphyrinoids, which contain several ether／phenol／pyrrole subunits, represent milestones in these molecular categories with unparalleled functional diversity. In contrast, macrocycles exploiting quinoline as a key unitary element to construct specific macrocyclic architecture have received limited attention and been barely explored. In this report, we summarize the recent advances in oligo─ quinoline macrocycles TriQuinoline (TQ), oxa─TriQuinoline (o─TQ), TEtraQuinoline (TEQ), and indole／quinoline hybrid macrocycle In2Q2. Particular emphasis is placed on the synthesis, structure, and application of these molecules in organometallic and supramolecular chemistry, which may guide new molecular designs in the heterocycle─based macrocycle family.

A new miniaturized framework for graphitic material featuring three neighboring pyridinic nitrogen atoms is disclosed. The quinoline/quinazoline hybridized pseudo trimeric macrocycle, DiQuinoline(Q)-MonoQuinazolines(Qz), Q2Qz1, was readily synthesized from the key macrocyclic amide precursor in a modular fashion. Its central cavity strongly captures a proton, and the thus-formed positively charged, highly planar architecture exhibits supramolecular complexation through π-interactions. Q2Qz1, with its unique properties, was applied as a scavenger for toxic polyaromatic hydrocarbons and as a G-quartet ligand for potential therapeutic agent for cancer chemotherapy.

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.

Porphyrin contains four inwardly oriented nitrogen atoms. It is arguably the most ubiquitous multifunctional naturally occurring macrocycle that has inspired the design of novel nitrogen-containing heterocycles for decades. While cyclic tetramers of pyrrole, indole, and pyridine have been exploited as macrocycles in this category, quinoline has been largely neglected as a synthon. Herein, we report the synthesis of TEtraQuinoline (TEQ) as a ‘missing link’ in this N4 macrocycle family. In TEQs, four quinoline units are concatenated to produce an S4-symmetric architecture. TEQs are characterized by a highly rigid saddle shape, wherein the lone-pair orbitals of the four nitrogen atoms are not aligned in a planar fashion. Nevertheless, TEQs can coordinate a series of transition-metal cations (Fe2+, Co2+, Ni2+, Cu2+, Zn2+, and Pd2+). TEQs are inherently fluorescence-silent but become strongly emissive upon protonation or complexation of Zn(II) cations (ϕ = 0.71). TEQ/Fe(II) complexes can catalyze dehydrogenation and oxygenation reactions with catalyst loadings as low as 0.1 mol %.

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.

A new 15-membered-macrocyclic molecular entity, oxa-TriQuinoline (o-TQ), was designed and synthesized. In o-TQ, three oxygen atoms were joined onto three quinoline units at the 2- and 8-positions in a head-to-tail fashion by three-fold SNAr reactions, giving rise to the characteristic N3O3 aza-oxa-crown architecture. o-TQ can serve as a new tridentate nitrogen ligand to capture a CuI cation and adopt a bowl shape, before supramolecular complexation with corannulene and [12]cycloparaphenylene (CPP) occurs through π–π and CH–π interactions. In the presence of the CuI cation, the non-emissive o-TQ becomes a highly emissive material in the solid state, whereby the emission wavelengths depend on the ancillary ligand on the CuI cation. The o-TQ/CuI complex is able to promote carbene catalysis to provide a range of enamines with a gem-difluorinated terminus.

An anti-selective catalytic asymmetric Michael-type vinylogous addition of β,γ-butenolides to chromones was developed. The catalyst system developed herein is characterized by tuning of the steric and electronic effects using a proper Biphep-type chiral ligand to invert the diastereoselection, and improvement of the catalyst turnover by a coordinative phenolic additive. The catalytic protocol renders potentially biologically active natural product analogs accessible in good yield with moderate diastereoselectivity and high enantiomeric purity, mostly greater than 99% ee. This journal is

The synthesis of (2R,3S)-3,4,4,4-tetrafluorovaline, a fluorinated derivative of the canonical α-amino acid l-valine, is reported for the first time. A highly enantio- and diastereoselective direct catalytic asymmetric Mannich-type reaction was applied as the key C–C bond-forming step to afford gram quantities of a central synthetic intermediate. The conformation of the novel fluorinated α-amino acid was analyzed by X-ray crystallography, NMR spectroscopy, and computational methods, which, together with its calculated and experimental physicochemical properties, indicated that the fluorinated valine is a bioisostere of l-isoleucine.

An efficient cooperative chiral Lewis acid/photoredox catalytic system for engaging highly reactive radicals in highly enantioselective conjugate addition to a,ß-unsaturated carbonyls is highly desirable. Direct photoexcitation of unbound substrates typically induces undesired background pathways for racemic products and remains a formidable challenge to be addressed in the area of enantioselective photocatalysis. Herein, we report a cooperative catalytic system comprising a chiral Cu(i) complex and an Ir(iii) photocatalyst fueled by visible-light irradiation that allows for seamless integration of the catalytic formation of a-amino alkyl radicals and subsequent enantioselective addition to a,ß-unsaturated amides. A 7-aza-6-MeO-indoline attachment on the amide substrates plays a pivotal role in suppressing the undesired pathways, resulting in excellent enantioselectivity and enabling expedited access to valuable ?-aminobutyramides. The indoline amide was readily diversified with full recovery of the azaindoline attachment, highlighting the synthetic utility of this cooperative catalytic system.