Annulene Derivatives Research Articles

Metal-free double azide addition to strained alkynes of an octadehydrodibenzo[12]annulene derivative with electron-withdrawing substituents.

Strain-promoted azide-alkyne cycloaddition (SpAAC) is a powerful tool in the field of bioconjugation and materials research. We previously reported a regioselective double addition of organic azides to octadehydrodibenzo[12]annulene derivatives with electron-rich alkyloxy substituents. In order to increase the reaction rate, electron-withdrawing substituents were introduced into octadehydrodibenzo[12]annulene. In this report, the synthesis of new octadehydrodibenzo[12]annulene derivatives, regioselective double addition of organic azides, and an application to crosslinking polymers are described.

Adsorption of Prochiral Solvent Molecules by Surface-Confined Chiral Supramolecular Assemblies: How Solvent Impacts on-Surface Chirality.

The understanding of supramolecular chirality in self-assembled molecular networks (SAMNs) on surfaces generates a lot of interest because of its relation to the production of chiral sensors, reactors, and catalysts. We herein report the adsorption of a prochiral solvent molecule in porous SAMNs formed by a chiral dehydrobenzo[12]annulene (cDBA) derivative. Through the prochirality recognition of a solvent molecule, the supramolecular chirality of the SAMN is switched: the cDBA exclusively forms a counter-clockwise pore through co-adsorption of the solvent molecule in prochiral 1,2,4-trichlorobenzene, while in 1-phenyloctane it produces the opposite chiral, clockwise pore. The prochirality recognition of the solvent molecule in the chiral SAMN pores is attributed to the adaptable conformational changes of the chiral chains of the cDBA molecule.

(n+3)-Cyclization for the Formation of Benzo[7]annulene Derivatives via a [1,4]-Hydride Shift: A Novel Cyclization Mode Involving an Internal Redox Reaction

AbstractWe report a unique synthetic route to benzo[7]annulene derivatives. When benzylidene malonates having a 1-(N,N-dialkylamino)alkyl group at the ortho-position are treated with a stoichiometric amount of M(OTf)3 (M = Sc, Yb, Gd), three transformations ([1,4]-hydride shift/isomerization into an enamine/intramolecular Stork enamine acylation) proceed sequentially to afford various benzo[7]annulene derivatives in moderate chemical yields. To our knowledge, the present reaction is the first example of an internal redox reaction involving a [1,n]-hydride shift/(n+3)-cyclization process.

Theoretical Studies on the Relationship between Aromaticity and Electron Transport Properties of Analogous [10]-Annulene Derivatives

In the overall aromaticity of a molecular system, the magnitude of [Formula: see text]-aromaticity influences the degree of bond length averaging in the molecular geometry, while the magnitude of [Formula: see text]-aromaticity reflects the strength of [Formula: see text]-electron delocalization, subsequently affecting the electronic transport properties of the entire molecular system. Simultaneously, the aromaticity type of a molecular system is primarily determined by the symmetry of the innermost [Formula: see text] molecular orbitals. In this study, we conducted computational simulations of the aromaticity and electronic transport properties of compounds, including C8H8Cu2 with [Formula: see text]–[Formula: see text] delocalization effects and C12H8 with [Formula: see text]–[Formula: see text] delocalization effects, along with their Li derivatives. Based on calculated NICS values, ring current directions, molecular structural configurations and the symmetry of the innermost [Formula: see text] molecular orbitals, we clarified the aromaticity types of the molecular systems. Combined with the analysis of molecular electrical conductivity properties, we gained insights into the fundamental attributes of Li-bridge bonds in Li derivatives and the factors influencing electronic transport pathways. Consequently, we established a relationship between the aromaticity of molecular systems and their electronic transport properties. To a certain extent, a novel criterion for evaluating molecular aromaticity is proposed from the perspective of single-molecule electronics.

Molecular islands at the liquid-solid interface.

Molecular islands of various shapes and sizes composed of a few tens of molecules only are formed at the liquid-solid interface, at room temperature, by an alkoxylated dehydrobenzo[12]annulene (DBA) derivative. Molecules are packed into hexagons. Scanning tunneling microscopy reveals the variety in molecular island structures and their stability. For molecular islands up to 7 hexagonal pores, all 244 possible structures are simulated and compared with experimental observations. Force field calculations give insights into the relative stability of the molecular islands and the factors contributing to it.

Photochemistry Driven by Excited-State Aromaticity Gain or Antiaromaticity Relief.

Gain of aromaticity or relief of antiaromaticity along a reaction path are important factors to consider in mechanism studies. Analysis of such changes along potential energy surfaces has historically focused on reactions in the electronic ground state (S0 ), but can also be used for excited states. In the lowest ππ* states, the electron counts for aromaticity and antiaromaticity follow Baird's rule where 4n π-electrons indicate aromaticity and 4n+2 π-electrons antiaromaticity. Yet, there are also cases where Hückel's rule plays a role in the excited state. The electron count reversals of Baird's rule compared to Hückel's rule explain many altered physicochemical properties upon excitation of (hetero)annulene derivatives. Here we illustrate how the gain of excited-state aromaticity (ESA) and relief of excited-state antiaromaticity (ESAA) have an impact on photoreactivity and photostability. Emphasis is placed on recent findings supported by the results of quantum chemical calculations, and photoreactions in a wide variety of areas are covered.

Synthesis of a highly aromatic and planar dehydro [10]annulene derivative

Synthesis of a highly aromatic and planar dehydro [10]annulene derivative

Insights into the Gold‐Catalyzed Cycloisomerization of 3‐Allyl‐1,4‐diynes for the Synthesis of Bicyclic Hydrocarbons

AbstractAn efficient protocol for the synthesis of 3‐ethynyl‐2‐aryl‐bicyclo[3.1.0]hexenes through a gold‐catalyzed enyne cyclization was established in this work. Depending on the specific substitution pattern, unusual cationic rearrangements of the corresponding gold carbene were revealed, leading to either cyclohexadienes or 5,9‐methanobenzo[8]annulene derivatives, respectively.

Searching for correlations between geometric and spectroscopic parameters of intramolecular hydrogen bonds in porphyrin-like macrocycles.

Chemical bond lengths and angles are characteristic structural parameters of a molecule. Similarly, the frequencies of the vibrational modes and the NMR chemical shifts are unique "chemical fingerprints" specific to a compound. These are the basic parameters describing newly obtained compounds and enabling their identification. Intramolecular hydrogen bonding significantly influences the physicochemical properties of macrocyclic compounds with a porphyrin-like structure. This work presents the verification for correlations between geometric and spectroscopic parameters related to hydrogen bonds in this type of macrocyclic compounds. In particular, such relationships were investigated for a large group of porphyrin, porphycene, and dibenzotetraaza[14]annulene derivatives and a group of other macrocycles with similar structure. A very strong linear correlation was found only between the vibrational frequencies of the NH groups involved in a hydrogen bond and the length of this bond, which applied to all macrocyclic compounds of this type. Several other relationships were found between spectroscopic (IR, Raman, NMR) and geometric (X-ray) parameters, highlighting differences and similarities between different families of macrocycles. Apart from providing a better understanding of the nature of hydrogen bonds and their characteristics in porphyrin-like macrocyclic compounds, these relationships will facilitate the identification of new macrocycles and the extrapolation of their spectroscopic properties.

Quinoxaline-annelated hexadehydro[12]annulene: use of a new building block to construct a hydrogen-bonded hexagonal molecular network

A new hexatopic carboxylic acid with a quinoxaline-annelated hexadehydro[12]annulene core (TQ12) was synthesized and subjected to spectroscopy for comparison with tribenzohexadehydro[12]annulene derivative (T12).

A Highly Strained Al-Al σ-Bond in Dianionic Aluminum Analog of Oxirane for Molecule Activation.

Since aluminum is the most electropositive element among the p-block elements, the construction of molecules bearing a dianionic Al-Al σ-bond is inherently highly challenging. Herein, we report the first synthesis of a dianionic dialane(6) 2 based on the Al2O three-membered ring scaffold, namely, an aluminum analog of oxirane. The structure of 2 has been unambiguously ascertained by spectroscopic analysis as well as X-ray crystallography, and computational studies revealed that 2 bears a highly strained Al-Al σ-bond. 2 readily reacts with the unsaturated substrates such as isocyanide, ethylene, and ketone, concomitant with the cleavage of the Al-Al σ-bond under mild conditions, leading to the four- and five-membered heterocycles 3-5. Furthermore, the reaction of 2 with two molecules of benzonitrile (PhCN) furnishes a seven-membered heterocycle 6, resulting from the C-C coupling reaction of PhCN. We further delineate that 2 selectively activates an arene ring C-C bond of biphenylene, rendering a di-Al-substituted benzo[8]annulene derivative 7. Preliminary computational studies propose that the stepwise reaction mechanism involves the Al-Al σ-bond cleavage, dearomative Al-C bond formation, subsequent sigmatropic [1,3]shifts, and a pericyclic reaction.

Synthesis of new metal‐free 1,2,4,5,9,10,12,13‐octaaza[16]annulene derivatives using the reaction of vinamidinium salts with thiocarbohydrazide

AbstractA new series of marcocyclic ligands, 1,2,4,5,9,10,12,13‐octaaza[16]annulene derivatives were synthesized by using the condensation reaction of the correspondingly [2+2] 2‐heteroaryl‐substituted vinamidinium salts or phenyl vinamidinium salts and derivatives or halo‐substituted vinamidinum salt [1A‐10A] with thiocarbohydrazide in ethanolic medium under mild condition. Metal complexes were formed by reacting of ethanolic solution of Co, Ni, and Zn with macrocyclic ligand in ethanolic medium under mild condition. Purposed complexes have been characterized with the help of elemental analyses, comparative absorption band of ν(C=N), mass, and NMR. Geometry and complex formulation are out of scope of this work. The biological activities of carohydrazide and thiocarbohydrazide base of the ligands and purposed complexes such as antimicrobial, antitumor, and insecticides have attracted significant attention in bioorganic chemistry.

An Approach to the Synthesis of a Two‐Dimensional Polymer Using a Preorganized Host‐Guest Network by Self‐Assembly at the Liquid/Solid Interface

AbstractAn approach to synthesize a two‐dimensional polymer (2DP) using a preorganized host‐guest network at the liquid/solid interface is presented. As a host network, we used a self‐assembled monolayer of a dehydrobenzo[12]annulene derivative having aminophenyl groups at three alkoxy chain ends and, as a guest, a hexakis(phenylethynyl)benzene derivative having six formyl groups, aiming to connect the host to the guest embedded in the host matrix by imine bond formation. STM observations of host‐guest mixtures with trifluoroacetic acid at the 1‐phenyloctane/highly oriented pyrolytic graphite interface revealed that the guest was observed as a spoke‐like feature in the nanowells. Based on the STM image analysis, short distances between the diagonal phenyl groups in the nanowells are detected, indicating that the imine bonds are formed. However, the small abundance and random distribution of the short phenyl‐phenyl distance indicate that the periodically ordered 2DP structure is not formed, probably because the network cannot tolerate the structural change due to partial bond formation.

Non-aromatic annulene-based aggregation-induced emission system via aromaticity reversal process

Aggregation-induced emission (AIE) is a photophysical phenomenon correlated closely with the excited-state intramolecular motions. Although AIE has attracted increasing attention due to the significant applications in biomedical and optoelectronics, an in-depth understanding of the excited-state intramolecular motion has yet to be fully developed. Here we found the non-aromatic annulene derivative of cyclooctatetrathiophene shows typical AIE phenomenon in spite of its rotor-free structure. The underlying mechanism is investigated through photoluminescence spectra, time-resolved absorption spectra, theoretical calculations, circular dichroism as well as by pressure-dependent fluorescent spectra etc., which indicate that the aromaticity reversal from ground state to the excited state serves as a driving force for inducing the excited-state intramolecular vibration, leading to the AIE phenomenon. Therefore, aromaticity reversal is demonstrated as a reliable strategy to develop vibrational AIE systems. This work also provides a new viewpoint to understand the excited-state intramolecular motion behavior of lumiongens.

Reversing the Handedness of Self‐Assembled Porous Molecular Networks through the Number of Identical Chiral Centres

AbstractScanning tunnelling microscope observations at the 1‐phenyloctane/graphite interface reveal how chiral structural information at the molecular level is transferred and expressed structurally at the 2D supramolecular level for a porous system. The chirality of self‐assembled molecular networks formed by chiral dehydrobenzo[12]annulene (cDBA) derivatives having three chiral chains and three achiral chains, alternatingly, is compared with those of cDBAs having six chiral chains reported previously. While for all cDBAs homochiral surfaces are formed, their handedness is not simply a reflection of the absolute configuration of the stereogenic centres. Both the number of stereogenic centres as well as the length of the achiral chains determine the supramolecular handedness, providing a deep insight into the supramolecular chirality induction mechanisms at play. Moreover, these cDBAs act to induce chirality in porous networks formed by achiral DBAs.

Reversing the Handedness of Self-Assembled Porous Molecular Networks through the Number of Identical Chiral Centres.

Scanning tunnelling microscope observations at the 1-phenyloctane/graphite interface reveal how chiral structural information at the molecular level is transferred and expressed structurally at the 2D supramolecular level for a porous system. The chirality of self-assembled molecular networks formed by chiral dehydrobenzo[12]annulene (cDBA) derivatives having three chiral chains and three achiral chains, alternatingly, is compared with those of cDBAs having six chiral chains reported previously. While for all cDBAs homochiral surfaces are formed, their handedness is not simply a reflection of the absolute configuration of the stereogenic centres. Both the number of stereogenic centres as well as the length of the achiral chains determine the supramolecular handedness, providing a deep insight into the supramolecular chirality induction mechanisms at play. Moreover, these cDBAs act to induce chirality in porous networks formed by achiral DBAs.

Strain‐Promoted Double Azide Addition to Octadehydrodibenzo[12]annulene Derivatives

AbstractOctadehydrodibenzo[12]annulenes (DBAs), readily available by the oxidative acetylenic coupling of 1,2‐diethynylbenzene derivatives, were reacted with organic azides. As compared to the well‐known strain‐promoted azide‐alkyne cycloaddition (SpAAC) of 5,6,11,12‐tetradehydrodibenzo[a,e][8]annulene, the reactivity of the DBA alkynes was lower due to the lower strain energy. However, the regioselective double azide addition occurred without any side reactions under mild conditions, yielding bis‐triazole products. The structures of the products were confirmed by an X‐ray crystal structure analysis, and the reaction mechanism was studied by 1H‐NMR spectroscopy and computational studies. It was also found that the DBAs were hardly fluorescent, while the bis‐triazole products showed a green fluorescence with quantum yields up to 5.1 %. Finally, the new strain‐promoted double azide addition to the DBAs was used for step‐growth polymerization, successfully producing a high molecular weight triazole polymer.

Gold and TfOH‐Cocatalyzed Tandem Reaction of ortho‐Akynylarylaldehydes with Cyclopropenes: an Efficient Route to Functionalized Benzo[7]annulene Derivatives

A novel gold(III) and TfOH‐cocatalyzed reaction of ortho‐alkynylbenzaldehydes with cyclopropenes was described for the synthesis of a variety of functionalized benzo[7]annulene derivatives in a highly stereoselective manner. This reaction could undergo tandem [4+2] cycloaddition/ring expansion to achieve the construction of seven‐membered‐carbocycles, along with the cleavage of double bond of cyclopropenes. The reaction features simple operations, commercially available catalysts and broad substrate scope with good efficiencies.

CO2 Sorption of Layered Hydrogen-bonded Organic Framework Causes Reversible Structural Changes Involving Four Different Crystalline States under Ambient Pressure

A layered hydrogen-bonded organic framework (T12-apo) composed of a dehydrotribenzo[12]annulene derivative T12 underwent as many as four states (S-1 to -4) reversibly during an hysteric CO2 sorptio...

Electrostatically Driven Guest Binding in a Self-Assembled Porous Network at the Liquid/Solid Interface.

We present here the construction of a self-assembled two-dimensional (2D) porous monolayer bearing a highly polar 2D space to study guest co-adsorption through electrostatic interactions at the liquid/solid interface. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, DBA-TeEG, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by p-phenylene linkers was synthesized. As a reference host molecule, DBA-C10, having nonpolar C10 alkyl chains at three alternating terminals, was employed. As guest molecules, hexagonal phenylene-ethynylene macrocycles (PEMs) attached by triethylene glycol (TEG) ester and hexyl ester groups, PEM-TEG and PEM-C6, respectively, at each vertex of the macrocyclic periphery were used. Scanning tunneling microscopy observations at the 1,2,4-trichlorobenzene/highly oriented pyrolytic graphite interface revealed that PEM-TEG was immobilized in the pores formed by DBA-TeEG at higher probability because of electrostatic interactions such as dipole-dipole and hydrogen bonding interactions between oligoether units of the host and guest, in comparison to PEM-C6 with nonpolar groups. These observations are discussed based on molecular mechanics simulations to investigate the role of the polar functional groups. When a nonpolar host matrix formed by DBA-C10 was used, however, only phase separation and preferential adsorption were observed; virtually no host-guest complexation was discernible. This is ascribed to the strong affinity between the guest molecules which form by themselves densely packed van der Waals networks on the surface.