Anti‐Aromatic versus Induced Paratropicity: Synthesis and Interrogation of a Dihydro‐diazatrioxa[9]circulene with a Proton Placed Directly above the Central Ring

We present a high‐yielding intramolecular oxidative coupling within a diazadioxa[10]helicene to give a dihydro‐diazatrioxa[9]circulene. This is the first [n]circulene containing more than eight ortho‐annulated rings (n>8). The single‐crystal X‐ray structure reveals a tight columnar packing, with a proton from a pendant naphthalene moiety centred directly above the central nine‐membered ring. This distinct environment induces a significant magnetic deshielding effect on that particular proton as determined by ¹H NMR spectroscopy. The origin of the deshielding effect was investigated computationally in terms of the NICS values. It is established that the deshielding effect originates from an induced paratropic ring current from the seven aromatic rings of the [9]circulene structure, and is not due to the nine‐membered ring being antiaromatic. UV/Vis spectroscopy reveals more efficient conjugation in the prepared diazatrioxa[9]circulene compared to the parent helical azaoxa[10]helicenes, and DFT calculations, including energy levels, confirm the experimental observations.     

Synthesis and 1H and 13C NMR spectra of 7-fluoro-, 9-fluoro- and 11-fluoro-benzo[b]fluoranthenes

We have synthesized 7-fluoro-, 9-fluoro- and 11-fluoro- benzo[b]fluoranthene as part of a study designed to locate the molecular sites involved in the metabolic activation of the carcinogenic parent hydrocarbon. Analysis of the proton NMR spectra reveals the effect of fluorine substitution to be almost entirely localized in the substituted ring, the principal exception being a strong deshielding of opposing protons in sterically crowded sites ($\text{i.e.}$, peri or pseudo-bay regions).     

The mass spectrometric behaviour of dimethylcyclosiloxanes

The fragmentations of [(CH₃)₂SiO]_n, (D_n), where n = 4, 5, 6, 7, 8, 9, 10, 12 and 15 are reported. The behaviour of these compounds under electron-impact is governed by the size of the siloxane ring. Rings smaller than D6 have base peaks corresponding to [M – 15]⁺ ions; larger rings all show base peaks of m/e 73 [Si(CH₃)₃]⁺. A transannular mechanism previously applied only to D₅ and D₆ is extended and modified to account for the behaviour of larger rings. A ring con-traction mechanism is proposed which leads to the formation of smaller rings and doubly charged ions. A new transannular mechanism is proposed to account for the production of [M – 177]⁺ and [M – 193]⁺ ions.     

Thermally curable benzoxazine monomer with a photodimerizable coumarin group

A new monomer, 4‐methyl‐9‐p‐tolyl‐9,10‐dihydrochromeno[8,7‐e][1,3]oxazin‐2(8H)‐one, possessing both benzoxazine and coumarin rings in its structure was synthesized by the reaction of 4‐methyl‐7‐hydroxycoumarin, paraformaldehyde, and p‐toluidine in methanol at 40 °C and characterized with spectral analysis. Upon photolysis around 300 nm, this monomer underwent dimerization via the [2πs+2πs] cycloaddition reaction. Photodimerization reactions were investigated with UV and ¹H NMR spectroscopy measurements. The thermal ring‐opening reaction of the benzoxazine ring was demonstrated with differential scanning calorimetry measurements. The thermal behavior of the cured product was also investigated with thermogravimetric analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1670–1676, 2007     

Per‐Substituted [8]Circulene and Its Non‐Planar Fragments: Synthesis,Structural Analysis,and Properties

The syntheses, structures, and physical properties of a full series of benzannulated tetraphenylenes are reported. The palladium‐catalyzed annulation of tetraiodo‐substituted 2,3,6,7,10,11,14,15‐octamethyltetraphenylene with insufficient di(4‐anisyl)ethyne yielded a mixture of per‐substituted [8]circulene and its non‐planar fragments, including mono‐, para‐di‐, ortho‐di‐, and triannulated products. Their structures were unambiguously verified by X‐ray crystallography. Successive benzannulations significantly affect the molecular geometries, dynamic behaviors, and physical properties of the compounds. In this series of compounds, [8]circulene is the most strained one, as reflected by the significant deplanarization of the phenanthrene moieties (ca. 63° in the bay region) and the fact that it has the highest strain energy (120.6 kcal mol^?1). The dynamic behaviors of these compounds were examined both experimentally and theoretically. The ring flipping of per‐substituted [8]circulene is confirmed to proceed through pseudorotation with a barrier of around 21 kcal mol^?1, whereas its non‐planar fragments require much more energy for the ring inversion. The photophysical and electrochemical properties of the investigated compounds depend strongly on the extent of efficient π conjugation. The successive benzannulations red‐shift both the absorption and the emission bands, and reduce the first oxidation potential.     

Highly Stable Radical Cations of N,N’-Diarylated Tetrabenzotetraaza[8]circulene

N,N’-Diarylated tetrabenzotetraaza[8]circulenes 3 a and 3 b were synthesized in good yields by a reaction sequence involving oxidation of tetrabenzodiazadithia[8]circulene 5-Oct and S_NAr reaction with aniline derivatives. The obtained aza[8]circulenes 3 a and 3 b were easily oxidized to give their radical cations 3 a⁺ and 3 b⁺ , which are highly stable under ambient conditions. X-ray diffraction analysis of radical cation 3 a⁺ showed a face-to-face dimer arrangement with an interplanar separation of 3.320 Å. The spin density of 3 a⁺ was calculated to be delocalized over the whole circulene π-systems with spin–spin exchange integral (J=−144 cm⁻¹) in the dimeric part. These radical cations displayed far red-shifted absorption bands reaching to 2000 nm. Thus this study has proved the hetero[8]circulene scaffold to be a new entry of promising electronics and spin materials.     

Compressing a Non-Planar Aromatic Heterocyclic [7]Helicene to a Planar Hetero[8]Circulene

This work describes a synthetic approach where a non-planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro-hetero[7]helicene, which is partially a helicene and partially a circulene: it is non-planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π-conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post-functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm).     

The NMR spectra of the carbanions of xanthene and thioxanthene. Evidence for paratropism

The proton NMR spectra of the carbanions of xanthene [XH]^? and thioxanthene [TxH]^? have been recorded and interpreted. Paratropism in the central rings of [XH]^? and [TxH]^? is inferred from a comparison of the chemical shifts with those of the carbanion of 9,10-dihydroanthracene [AH]^?. The contributions to the chemical shifts arising from n-electron excess charges, local dipoles and magnetic anisotropies are discussed. Numerical values for the various ring currents have been estimated by a least squares analysis of the observed chemical shifts after applying corrections for the excess charge effect. The results point to a strongly increasing paramagnetic ring current in the central ring in the order [AH]^?, [TxH]^?, [XH]^?.     

Höhere,kondensierte Ringsysteme. 5. Mitteilung[1]. Makrocyclen mit überbrückten 9, 10-Dihydrophenanthreneinheiten

Starting from 2, 7-diacetyl-9, 10-dihydrophenanthrene, 2, 7-dichloromethyl-9, 10-dihydrophenanthrene was synthesized through a serie of a new compounds. By a modified Wurtz reaction the dichloromethyl compound led to hexahydro-[2³] (2,7) phenanthrenophane and decahydro-[2⁵] (2,7) phenanthrenophane. [2³] (2,7) phenanthrenophane was obtained by dehydrogena tion of hexahydro-[2³] (2,7) phenanthrenophane with Pd/C. The structure of these new ring systems was confirmed by UV.-, NMR.- and mass spectroscopy.     

How To Reach Intense Luminescence for Compounds Capable of Excited‐State Intramolecular Proton Transfer?

Photoinduced intramolecular direct arylation allows structurally unique compounds containing phenanthro[9′,10′:4,5]imidazo[1,2‐f]phenanthridine and imidazo[1,2‐f]phenanthridine skeletons, which mediate excited‐state intramolecular proton transfer (ESIPT), to be efficiently synthesized. The developed polycyclic aromatics demonstrate that the combination of five‐membered ring structures with a rigid arrangement between a proton donor and a proton acceptor provides a means for attaining large fluorescence quantum yields, exceeding 0.5, even in protic solvents. Steady‐state and time‐resolved UV/Vis spectroscopy reveals that, upon photoexcitation, the prepared protic heteroaromatics undergo ESIPT, converting them efficiently into their excited‐state keto tautomers, which have lifetimes ranging from about 5 to 10 ns. The rigidity of their structures, which suppresses nonradiative decay pathways, is believed to be the underlying reason for the nanosecond lifetimes of these singlet excited states and the observed high fluorescence quantum yields. Hydrogen bonding with protic solvents does not interfere with the excited‐state dynamics and, as a result, there is no difference between the occurrences of ESIPT processes in MeOH versus cyclohexane. Acidic media has a more dramatic effect on suppressing ESIPT by protonating the proton acceptor. As a result, in the presence of an acid, a larger proportion of the fluorescence of ESIPT‐capable compounds originates from their enol excited states.     

Synthesis,structural and conformational study of some esters derived from 8-phenethyl-8-azabicyclo[4.3.1]decan-10α-ol

A series of 10α-acyloxy-N-phenethyl-8-azabicyclo[4.3.1]decane derivatives have been synthesized and studied by ¹H and ¹³C nmr spectroscopy, and the crystal structure of N-phenethyl-10aL-(xanten-9″-carbonyloxy)bicyclo[4.3.1]decane 2 has been determined by X-ray diffraction. The compounds studied display in deuteriochloroform the same preferred conformation adopted by the piperidine ring as a distorted chair conformation flattened at N-8 with both the phenethyl and acyloxy groups in the equatorial position with respect to the piperidine ring. These results are in close agreement with that found for compound 2 in the crystalline state.     

Synthesis,crystal structure and complexation behaviour of a thiacalix[4]arene bearing 1,2,3-triazole groups

The structure and complexation behaviour of 1,3-alternate-1,2,3-triazole based on thiacalix[4]arene,1,3-alternate-1 and 2 have been determined by means of X-ray analysis, fluorescence and ¹H NMR spectroscopy. The X-ray results suggested that the nitrogen atom N3 on triazole ring can act as hydrogen bond acceptors in the self-assembly of a supramolecular structure. The fluorescence spectra changes indicated that the thiacalix[4]arene bearing 1,2,3-triazole groups were highly selective for Ag⁺ in comparison with other tested metal ions by enhancement of the monomer emission of pyrene. The ¹H NMR results suggested that Ag⁺ can be strongly bonded by the triazole groups with the cooperation of the ionophoric cavity formed by the two inverted benzene rings and the sulfur atoms of the thiacalix[4]arene.     

Consequences of Curvature on Induced Magnetic Field: The Case of Helicenes

Helicenes consist of several fused rings twisted around an axis, forming a cylindrical helix, with π-delocalized electrons in the non-planar rings. Induced magnetic fields dissecting the orbital contributions of [6]-, [7]-, and [14]helicene are discussed. Computations show a deshielding cone produced by the π-electrons along the helical axis. Unexpectedly, the response of the core electrons produces a shielding cone, which is cumulative and sensitive to the curvature of the systems owing to the overlap of the other ring responses. A warning is provided regarding the evaluation of the delocalization in curved systems in which the x- and y-components of the induced magnetic field become relevant.     

Preparation and characterization of 16-benzoylated tetraaza[14]annulenes

The condensation reaction between tetraaza[14]annulene ( 1 ) and a series of para-substituted benzoyl chlorides led to the 16-benzoylated corresponding products in 13–21% yields, but 1 was unreactive with alkyl acid chlorides and easily cleaved in macrocyclic framework. The mass spectra show the presence of molecular ion peaks which support the 16-benzoylated products. A strong ir band due to the C = N stretching mode of the macrocyclic moiety was observed at 1610 cm^?1 and shifted slightly toward higher energy upon benzoylation. An intense ir band which was associated with a C = 0 stretching mode was newly observed at 1640 cm¹. The very strong absorption band about 29000 cm^?1 was attributed to the π ? π* transition and gave a slight shift to higher frequency on benzoylation. All proton signals except for methyl protons exhibit downfield shifts due to the deshielding effect of the substituted benzene ring, but the methyl proton peaks show upfield shifts due to the shielding effect caused by the magnetic anisotropy of the substituted benzene ring. The ¹³C nmr result is also in accord with that of ¹H nmr.     

Host–guest interactions of thiabendazole with normal and modified cucurbituril: 1H NMR,phase solubility and antifungal activity studies

Guest–host inclusion complexes between thiabendazole (TBZ) and cucurbit[7]uril (Q[7]), symmetrical tetra-methylcucurbit[6]uril (TMeQ[6]) and meta-hexamethyl-substituted cucurbit[6]uril (HMeQ[6]) in aqueous solution were investigated by ¹H NMR spectroscopy and phase solubility studies. The antifungal activities of the inclusion complexes were also determined. Analysis of the ¹H NMR spectra revealed that the host Q[7] selectively binds the benzimidazole ring moiety of the guest molecule and that the thiazole ring is encapsulated into the cavities of TMeQ[6] and HMeQ[6]. Phase solubility diagrams were analysed using rigorous procedures to obtain estimates of the complex formation constants for Q[n]-TBZ complexation. The phase solubility studies showed that TBZ solubility increased as a function of Q[7], TMeQ[6] and HMeQ[6] concentrations. We found that complexation of TBZ with Q[n] increased the inhibitory effect of TBZ on the growth of Fusarium graminearum. Our results thus demonstrate that complexation of TBZ with Q[n] could be used to improve the solubility and antifungal activity of TBZ.     

catena‐Poly[[diisothio­cyanato­cad­mium(II)]‐bis­[μ‐1,3‐bis­(1,2,4‐triazol‐1‐ylmeth­yl)benzene‐κ2N4:N4′]]: a double‐chain coordination polymer

The coordination geometry of the Cd^II atom in the title complex, [Cd(NCS)₂(C₁₂H₁₂N₆)₂]_n or [Cd(NCS)₂(mbtz)₂]_n, where mbtz is 1,3‐bis­(1,2,4‐triazol‐1‐ylmeth­yl)benzene, is a distorted compressed octa­hedron in which the Cd^II atom lies on an inversion centre, coordinated by four N atoms from the triazole rings of four mbtz ligands and two N atoms from two monodentate NCS⁻ ligands. The structure is polymeric, with 24‐membered spiro‐fused rings extending along [100] and with the 24‐membered ring containing two inversion‐related mbtz mol­ecules.     

Dianthracenylazatrioxa[8]circulene: Synthesis,Characterization and Application in OLEDs

A soluble, green-blue fluorescent, π-extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6-dihydroxycarbazole and 1,4-anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent-dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material. The presence of sliding π-stacked columns in the single crystal of dianthracenylazatrioxa[8]circulene is found to cause a very high electron-hopping rate, thus making this material a promising n-type organic semiconductor with an electron mobility predicted to be around 2.26 cm² V⁻¹ s⁻¹. The best organic light-emitting diode (OLED) device based on the dianthracenylazatrioxa[8]circulene fluorescent emitter has a brightness of around 16 000 Cd m⁻² and an external quantum efficiency of 3.3 %. Quantum dot-based OLEDs were fabricated by using dianthracenylazatrioxa[8]circulene as a host matrix material.     

Supramolecular Detoxification of Colchicine through Electrochemical Recognition

The complex characteristics of p-sulfonated calix[n]arene and colchicine were examined using various techniques. Cyclic voltammetry indicated that the structural matching and electrostatic interactions were the dominant stabilizing factors for the host–guest complexes. The method showed a long linear voltammetric range for p-sulfonated calix[4]arene from 1?×?10^?8 to 1?×?10^?6?mol?L^?1 with a detection limit of 3?×?10^?9?mol?L^?1. Ultraviolet absorption spectroscopy confirmed that a 1:1 ratio complex was formed. Molecular mechanics showed that the benzene ring of colchicine entered the p-sulfonated calix[4]arene cavity. The solubility of colchicine increased with the p-sulfonated calix[4]arene concentration 50-fold from 0.13 to 6.4?mol?L^?1. The simulation of cell membrane permeability indicated that colchicine was released from the colchicine-p-sulfonated calix[4]arene complex and entered the hydrophobic micelles. These results show that p-sulfonated calix[4]arene is suitable as a drug carrier for colchicine. This work has expanded applications of drug loading, transport, and targeted release for the treatment of gout.     

Methylierung von 4-Hydroxy-4-(2-piperidyl)-4H-pyrazolo [1,5-a]indol mit Formaldehyd und Ameisensäure. 11. Mitteilung über metallorganische Reaktionen und Folgeprodukte

In the 10^th communication of this series [1] the synthesis of 4-hydroxy-4-(2-piperidyl)-4H-pyrazolo[1,5-a]indole ( 4 ) was described (Scheme). Surprisingly enough, methylation of this compound with formaldehyde and formic acid led via ring closure and a subsequent rearrangement to a pentacyclic ketone. By means of ¹³C-NMR.-spectroscopy and mass spectroscopy, this ketone could be identified as a indolizino-pyrazolo-indole ( 9 ). Its structure and configuration were determined by X-ray structure analysis.     

Nitrogen bridgehead compounds. Part 80 unusual reaction of ethyl 9-bromo-4-oxo-6,7,8,9-tetr ahydro-4h-pyrido[1,2-a]pyrimidine-3-carboxylates and N-Methylaniline

The acid-catalysed intramolecular nucleophilic addition of the phenyl ring to the C(9a) = N(1) double bond of ethyl 9-(N-methyl-N-phenyl)-4-oxotetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates, formed in the reactions of ethyl 9-bromo-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates and N-methylaniline, gave the first examples of a new tetracyclic pyrimido[1′,2′:1,2]pyrido[3,2-b]indole ring system ( 7 ). X-ray diffraction analysis of 7a revealed that the annelation of the pyrimidine and piperidine rings is transoid, while that of the piperidine and pyrroline rings is cis, the piperidine ring adopts an unusual ⁶T₈ twisted boat conformation, while the pyrroline ring has a ⁹T_8a conformation.