Polycyclic Frameworks Research Articles

Intramolecular/Intermolecular Sequential Cyclization Accompanied by Double C-F Bond Cleavage: Access to Tricyclic Fluorine-Containing Pyrano[3,2-c]chromenes.

Defluorinative cyclization of CF3-alkenes has emerged as a reliable strategy for crafting intricate polycyclic frameworks. In this study, a facile defluorinative bicyclization approach was developed for the construction of 4H,5H-pyrano[3,2-c]chromenes under mild conditions involving a sequence of intramolecular cyclization and intermolecular defluoroheterocyclization. A variety of polysubstituted 4H,5H-pyrano[3,2-c]chromenes featuring C2-fluorine could be synthesized in good yields with excellent tolerance toward various functional groups. Moreover, the introduction of a C-F bond provides additional possibilities for further modification of this skeleton. The product features aggregation-induced emission (AIE) characteristics after simple modification, which is promising for chemical and biomedical imaging.

Design and Synthesis of Out/Out, Out/In, and In/In Epoxides in Polycyclic Cage Frameworks

AbstractWe report a useful synthetic approach to assemble in/in epoxide, in/out epoxide, and out/out epoxide in cage systems using the Corey–Chaykovsky reaction and the Peterson olefination as key steps. In this regard, a variety of pentacycloundecane (PCUD) based cage compounds containing oxirane rings with diverse stereochemical disposition were synthesized via a simple synthetic sequence. Five cage diones were used for this purpose, and the starting cage diones were prepared with easily accessible starting materials such as 1,4-hydroquinone derivatives and cyclopentadiene. Here, we have used the Diels–Alder (DA) reaction, a [2+2] photocycloaddition, the Corey–Chaykovsky reaction, and the Peterson olefination as crucial steps to prepare the target molecules.

(Invited) An Unsymmetrical 5,15-Disubstituted Tetrabenzoporphyrin: Effect of Molecular Symmetry on the Packing Structure and Charge Transporting Property

One of the key issues in the development of organic field-effect transistor (OFET) materials is the improvement of charge mobility. Since charge mobility depends on intermolecular interactions in solid state, it is important to control the crystal structure. In the current mainstream OFET materials, such as acenes and heteroacenes, which have one-dimensionally (1D) extended polycyclic aromatic frameworks, the effect of substitution on the crystal structure has been intensively studied. On the other hand, some bulky (trialkylsilyl)ethynyl-substituted derivatives such as 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) have been known to afford brickwork packing. In comparison, two-dimensionally (2D) extended π-conjugated molecules tend to form a sandwich herringbone, a co-facial herringbone, and a 1D columnar structure, due to their enhanced π−π interaction. The molecular design strategy to control the crystal structure of two-dimensional (2D) π-extended organic semi-conductors has not been intensively explored.We synthesized an unsymmetric tetrabenzoporphyrin derivative (TIPS-Ph-BP) to demonstrate the effect of molecular symmetry on crystal packing.1 An unsymmetric structure would make 2D π-stacking more stable than a one-dimensional (1D) columnar structure to counteract steric and electronic imbalance in the crystal. TIPS-Ph-BP formed an antiparallel slipped π-stacking and 2D herringbone-like structure as expected, but, it formed a dimeric herringbone packing consisting of slipped π-stacking in an antiparallel manner in the crystal. OFETs using TIPS-Ph-BP achieved the maximum hole mobility of 0.71 cm2 V-1 s-1 due to the partially 2D packing structure.Although TIPS-Ph-BP gave dimeric herringbone packing, this strategy could be used to control the crystal structures of various 2D extended π-conjugated systems. Further modification of the porphyrin substituents is ongoing. Reference K. Miyazaki, K. Matsuo, H. Hayashi, M. Yamauchi, N. Aratani, H. Yamada, Org. Lett. 2023, 25, 7354-7358

Construction and Modification of Nitrogen-Rich Polycyclic Frameworks: A Promising Fused Tricyclic Host-Guest Energetic Material with Heat Resistance, High Energy, and Low Sensitivity.

The construction and modification of novel energetic frameworks to achieve an ideal balance between high energy density and good stability are a continuous pursuit for researchers. In this work, a fused [5,6,5]-tricyclic framework was utilized as the energetic host to encapsulate the oxidant molecules for the first time. A series of new pyridazine-based [5,6] and [5,6,5] fused polycyclic nitrogen-rich skeletons and their derivatives were designed and synthesized. Two strategies, amino oxidation and host-guest inclusion, were used to modify the skeleton in only one step. All compounds exhibit good comprehensive properties (Td(onset) > 200 °C, ρ > 1.85 g cm-3, Dv > 8400 m s-1, IS > 20 J, FS > 360 N). Benefiting from the pyridazine-based fused tricyclic structure with more hydrogen bonding units and larger conjugated systems, the first example of [5,6,5]-tricyclic host-guest energetic material triamino-9H-pyrazolo[3,4-d][1,2,4]triazolo[4,3-b]pyridazine-diperchloric acid (10), shows high decomposition temperature (Td(onset) = 336 °C), high density and heats of formation (ρ = 1.94 g cm-3, ΔHf = 733.4 kJ mol-1), high detonation performance (Dv = 8820 m s-1, P = 36.2 GPa), high specific impulse (Isp = 269 s), and low sensitivity (IS = 30 J, FS > 360 N). The comprehensive performance of 10 is superior to that of high-energy explosive RDX and heat-resistant explosives such as HNS and LLM-105. 10 has the potential to become a comprehensive advanced energetic material that simultaneously satisfies the requirements of high-energy and low-sensitivity explosives, heat-resistant explosives, and solid propellants. This work may give new insights into the construction and modification of a nitrogen-rich polycyclic framework and broaden the applications of fused polycyclic framework for the development of host-guest energetic materials.

Helically Chiral π-Expanded Azocines Through Regioselective Beckmann Rearrangement and Their Charged States.

We report a synthetic approach to π-expanded [6]helicenes incorporating tropone and azocine units in combination with a 5-membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8-membered lactam, azocine, and amine units. As shown by X-ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state. The compounds exhibit promising optoelectronic properties with considerable photoluminescence quantum yields and tunable emission wavelengths depending on the relative position of the nitrogen center within the polycyclic framework. Separation of the enantiomers by chiral high-performance liquid chromatography (HPLC) allowed characterization of their chiroptical properties by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The azocine compounds feature manifold redox chemistry, allowing for the characterization of the corresponding radical anions and cations as well as the dications and dianions, with near-infrared (NIR) absorption bands extending beyond 3000 nm. Detailed theoretical studies provided insights into the aromaticity evolution upon reduction and oxidation, suggesting that the steric strain prevents the azocine unit from undergoing aromatization, while the indene moiety dominates the observed redox chemistry.

Helically Chiral π‐Expanded Azocines Through Regioselective Beckmann Rearrangement and Their Charged States

AbstractWe report a synthetic approach to π‐expanded [6]helicenes incorporating tropone and azocine units in combination with a 5‐membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8‐membered lactam, azocine, and amine units. As shown by X‐ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state. The compounds exhibit promising optoelectronic properties with considerable photoluminescence quantum yields and tunable emission wavelengths depending on the relative position of the nitrogen center within the polycyclic framework. Separation of the enantiomers by chiral high‐performance liquid chromatography (HPLC) allowed characterization of their chiroptical properties by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The azocine compounds feature manifold redox chemistry, allowing for the characterization of the corresponding radical anions and cations as well as the dications and dianions, with near‐infrared (NIR) absorption bands extending beyond 3000 nm. Detailed theoretical studies provided insights into the aromaticity evolution upon reduction and oxidation, suggesting that the steric strain prevents the azocine unit from undergoing aromatization, while the indene moiety dominates the observed redox chemistry.

A general strategy for the synthesis of taxane diterpenes.

The carbon skeleton of any organic molecule serves as the foundation for its three-dimensional structure, playing a pivotal role in determining its physical and biological properties1. As such, taxane diterpenes are one of the most well-known natural product families, primarily owing to the success of their most prominent compound, paclitaxel, an effective anticancer therapeutic for more than 25 years2-6. In contrast to classical taxanes, the bioactivity of cyclotaxanes (also referred to as complex taxanes) remains significantly underexplored. The carbon skeletons of these two groups of taxanes differ significantly, and so would typically their own distinct synthetic approaches. Here we report a versatile synthetic strategy based on the interconversion of complex molecular frameworks, providing general access to the wider taxane diterpene family. A range of classical and cyclotaxane frameworks was prepared including, among others, the total syntheses of taxinine K (2), canataxapropellane (5) and dipropellane C from a single advanced intermediate. The synthetic approach deliberately eschews biomimicry, emphasizing instead the power of stereoelectronic control in orchestrating the interconversion of polycyclic frameworks.

Symmetry-breaking charge separation in a null-excitonic 3-dimensional rigid nonconjugated trimer.

Photoinduced symmetry-breaking charge separation (SB-CS) has been extensively observed in various oligomers and aggregates, which holds great potential for robust artificial solar energy conversion systems. It attaches great importance to the precise manipulation of interchromophore electronic coupling in realizing efficient SB-CS. The emerging studies on SB-CS suggested that it could be realized in null-excitonic aggregates, and a long-lived SB-CS state was observed, which offers an advanced platform and has gathered immense attention in the SB-CS field. Here, we unveiled the null-exciton coupling induced ultrafast SB-CS in a rigid polycyclic aromatic hydrocarbon framework, triperyleno[3,3,3]propellane triimides (TPPTI), in which three chromophores were attached through a nonconjugated bridge. Through a combination of theoretical calculations and steady-state absorption results, we demonstrated that this nonconjugated TPPTI possesses negligible exciton coupling. Increased solvent polarity was found to significantly enhance state mixing between local excited and charge transfer states. Using transient absorption spectroscopy, ultrafast SB-CS was observed in highly polar dimethylformamide, facilitated by a selective hole-transfer coupling and a favorable charge separation free energy (ΔGCS). Additionally, the rate ratio between SB-CS and charge recombination was at least high to 1800 in dimethylformamide. This investigation provides profound insights into the role of null-exciton coupling in dominating ultrafast SB-CS in multichromophoric systems.

Synthesis, Structures and Properties of Trioxa[9]circulene and Diepoxycyclononatrinaphthalene

AbstractThis article presents trioxa[9]circulene (3) as a novel member of hetero[n]circulenes. Its synthesis began with the synthesis of dimethoxydioxa[8]helicene (5) and used dimethoxydiepoxycyclononatrinaphthalene (4) as a key intermediate, despite the condensation reaction predominantly yielding a 1,4‐addition byproduct. The structures and properties of 3–5 were extensively investigated using experimental and computational methods. Analysis of the crystal structures reveal elongation of the internal C−C bonds in the nine‐membered ring of 3 compared to 4 and 5. Computational studies demonstrate the remarkable flexibility of trioxa[9]circulene's saddle‐shaped polycyclic framework, while the other two compounds are rigid with large racemization barriers. Optically pure forms of 4 and 5 exhibit absorption and luminescence dissymmetry factors on the order of 10−2, with smaller values observed for compound 4. In the crystal structures, molecules of 3 stack to form columns with remarkable π–π overlap, and the π–π interactions of 4 exhibit short intermolecular C‐to‐C contacts. Consequently, the solution‐processed film of 4 functioned as a p‐type organic semiconductor in field effect transistors.

Synthesis, Structures and Properties of Trioxa[9]circulene and Diepoxycyclononatrinaphthalene.

This article presents trioxa[9]circulene (3) as a novel member of hetero[n]circulenes. Its synthesis began with the synthesis of dimethoxydioxa[8]helicene (5) and used dimethoxydiepoxycyclononatrinaphthalene (4) as a key intermediate, despite the condensation reaction predominantly yielding a 1,4-addition byproduct. The structures and properties of 3-5 were extensively investigated using experimental and computational methods. Analysis of the crystal structures reveal elongation of the internal C-C bonds in the nine-membered ring of 3 compared to 4 and 5. Computational studies demonstrate the remarkable flexibility of trioxa[9]circulene's saddle-shaped polycyclic framework, while the other two compounds are rigid with large racemization barriers. Optically pure forms of 4 and 5 exhibit absorption and luminescence dissymmetry factors on the order of 10-2, with smaller values observed for compound 4. In the crystal structures, molecules of 3 stack to form columns with remarkable π-π overlap, and the π-π interactions of 4 exhibit short intermolecular C-to-C contacts. Consequently, the solution-processed film of 4 functioned as a p-type organic semiconductor in field effect transistors.

Chemoselective Oxypalladation of (o‐Alkynylaryl)amide‐Triggered Site‐Selective C−H Annulation for Stereoselective Synthesis of Succinimide‐Fused Polycycles

AbstractWe report herein a palladium‐catalyzed, site‐selective cyclative annulation of o‐alkynyl arylamides with maleimide for the stereoselective construction of succinimide‐fused benzoxazine derivatives. This operationally simple and modular protocol provides access to polycyclic frameworks. The other associated features are high functional group compatibility, gram‐scale synthetic potential, and downstream transformations. Control and labeling experiments were conducted to get insights into the mechanism.

Holotrichones A and B, potent anti-leukemic lindenane-type sesquiterpene trimers with unprecedented complex carbon skeletons from a rare Chloranthus species

Two lindenane-type sesquiterpene (LDS) trimers with unprecedented carbon skeletons, holotrichones A (1) and B (2), were obtained from the whole plant of Chloranthus holostegius var. trichoneurus by a ultra performance liquid chromatography-photodiode array detector-mass spectrometry (UPLC-PDA-MS)-guided isolation strategy. Compound 1 represents the first LDS trimer incorporating a unique 3/5/6/6-fused framework, in which a lindenane-type monomer and the 2-methylbutyryl substituent of an LDS dimer is bridged by a six-membered ring system. Compound 2 is the first hetero-trimer fused by an LDS dimer with a p-benzoquinone-meroterpenoid, featuring an unusual 3/5/6/6/3/5/6/6/6 nonacyclic system fused by the sesquiterpenoid unit and a 2-geranyl-6-methyl-2,5-cyclohexadien-1,4-dione moiety. In compound 2, the dimeric LDS moiety is equipped with a rare oxaspiro[4.5]decane system. Their structures, including absolute configurations, were established by spectroscopic methods, GIAO NMR calculations and DP4+ probability analyses, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analysis. The plausible biogenetic pathway speculation indicated that hetero- and homo-Diels-Alder additions may dominate the formation of these highly fused polycyclic frameworks. Both compounds 1 and 2 induced the human acute myeloid leukemia MV-4–11 cell death via apoptosis induction, which deserves further investigation on this new chemical class of LDS oligomers for their anti-leukemic potential.

Unveiling Three Interconvertible Redox States of Boraphenalene.

Neutral 1-boraphenalene displays the isoelectronic structure of the phenalenyl carbocation and is expected to behave as an attractive organoboron multi-redox system. However, the isolation of new redox states have remained elusive even though the preparation of neutral boron(III)-containing phenalene compounds have been extensively studied. Herein, we have adopted an N-heterocyclic carbene ligand stabilization approach to achieve the first isolation of the stable and ambipolar 1-boraphenalenyl radical 1•. The 1-boraphenalenyl cation 1+ and anion 1- have also been electrochemically observed and chemically isolated, representing new redox forms of boraphenalene for the study of non-Kekulé polynuclear benzenoid molecules. Experimental and theoretical investigations suggest that the interconvertible three-redox-state species undergo reversible electronic structure modifications, which primarily take place on the polycyclic framework of the molecules, exhibiting atypical behavior compared to known donor-stabilized organoboron compounds. Initial reactivity studies, aromaticity evaluations, and photophysical studies show redox-state-dependent trends. While 1+ is luminescent in both the solution and solid states, 1• exhibits boron-centered reactivity and 1- undergoes substitution chemistry on the boraphenalenyl skeleton and serves as a single-electron transfer reductant.

Enhancing blue TADF narrow-band emission via tandem OLEDs with optical modeling simulation

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials, based on polycyclic aromatic frameworks, have shown promise in achieving narrow-band emission and high luminous efficiency. In this study, we investigate the performance of a blue MR-TADF material, 2′2'2''-(1,3,5-triazine-2,4,6-triyl) tris(9-(2-(naphthalen-2-yl)phenyl)-9H-carbazole) (TBN-TPA), in tandem OLED devices. Single emitter unit and two emitter unit tandem OLED devices with blue MR-TADF material were explored with optical modeling simulation. More importantly, the tandem architecture assists in realizing narrow-band emission and high color purity via optical interference and microcavity effects, which are essential for meeting BT 2020 standards. TBN-TPA achieves narrow full width at half maximum down to 24 nm and CIE coordinates approaching the blue region in tandem devices. Our work highlights the significant advantages of combining tandem architectures and emerging MR-TADF emitters for developing high-performance OLEDs with both high efficiency and wide color gamut. This is the first demonstration of using tandem OLED architecture to improve both efficiency and color purity of a blue multi-resonance TADF emitter. Further research on optimizing tandem structures and designing advanced MR-TADF materials will promote the applications of OLED displays.

Inside Back Cover

Cobalt, as a naturally highly abundant first row (3d) transition metal, has emerged as versatile, efficient and less toxic catalyst for C—H bond activation to construct polycyclic molecular frameworks. The cover image depicts the selective synthesis of spiro indene‐2,1'‐isoindolinones and spiro isochroman‐3,1'‐isoindolinones via cobalt‐catalyzed switchable [4 + 1] and [4 + 1 + 1] spirocyclization of aromatic amides with 2‐diazo‐1H‐indene‐1,3(2H)‐dione. More details are discussed in the article contributed by Li and Fan et al. on page 363—369.image

Dearomative difunctionalization of arenes via highly selective radical relay reactions

Dearomatization of arenes emerges as a reliable strategy for crafting intricate 3D polycyclic frameworks.

ANTI-INFLAMMATORY AND ANALGESIC ACTIVITY OF AZAADAMANTANES - ANALOGUES OF AMANTADINE

The anti-inflammatory and analgesic activity of three azaadamantane analogues of amantadine 1 was investigated. The tested azaadamantanes containing nitrogen atoms in the polycyclic framework were: 5,7-dimethyl-1,3-diazaadamantane-6-one 2, 6-amino-5,7-dimethyl-1,3-diazaadamantane 3 and 7-amino-1,3,5-triazaadamantane 4. Experiments were carried out on male mice of CD1 and CBA lines. Compounds were administered intraperitoneally at doses of 20 and 50 mg/kg. Anti-inflammatory activity was studied on the standard models of inflammatory edema induced by histamine or concanavaline inflammation by injecting the phlogogens in the aponeurosis of the hind paw of mice. The analgesic activity was assessed using the hot plate and acetic writhing tests. It is shown that the introduction of heteroatoms into the adamantane core does not reduce the anti-inflammatory activity of diazaadamantanes (2, 3) and enhances that of triazaadamantane (4) compared to amantadine. Modification of the adamantane backbone with nitrogen atoms leads to a change in the analgesic properties of the molecule, which is manifested as hyperalgesia in the acetic writhing test. This phenomenon is presumably related to the effect of azaadamantanes on nocigenic transient receptor potential channels (TRPV1).

A Conformationally Stable π-Expanded X-Type Double Helicene Comprising Dihydropyracylene Units with Multistage Redox Behavior.

A π-expanded X-type double [5]helicene comprising dihydropyracylene moieties was synthesized from commercially available acenaphthene. X-ray crystallographic analysis revealed the unique highly twisted structure of the compound resulting in the occurrence of two enantiomers which were separated by chiral HPLC, owing to their high conformational stability. The compound shows strongly bathochromically shifted UV/vis absorption and emission bands with small Stokes shift and considerable photoluminescence quantum yield and circular polarized luminescence response. The electrochemical studies revealed five facilitated reversible redox events, including three reductions and two oxidations, thus qualifying the compound as chiral multistage redox amphoter. The experimental findings are in line with the computational studies based on density functional theory pointing towards increased spatial extension of the frontier molecular orbitals over the polycyclic framework and a considerably narrowed HOMO-LUMO gap.

A Rigid Multiple Resonance Thermally Activated Delayed Fluorescence Core Toward Stable Electroluminescence and Lasing.

The investigation of organic light-emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple-resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (<30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm-2 . Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet-triplet annihilation under long-pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo-stability resulted in improved lasing and electroluminescence stability compared to that of 5,9-diphenyl-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (DABNA)-core. These findings indicate the potential of CzBN-core as a promising framework for achieving long-pulsed wave and electrically-pumped lasing in the future.

A Rigid Multiple Resonance Thermally Activated Delayed Fluorescence Core Toward Stable Electroluminescence and Lasing

AbstractThe investigation of organic light‐emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple‐resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (&lt;30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm−2. Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet‐triplet annihilation under long‐pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo‐stability resulted in improved lasing and electroluminescence stability compared to that of 5,9‐diphenyl‐5,9‐diaza‐13b‐boranaphtho[3,2,1‐de]anthracene (DABNA)‐core. These findings indicate the potential of CzBN‐core as a promising framework for achieving long‐pulsed wave and electrically‐pumped lasing in the future.