Heterocyclic Benzo Research Articles

Benzo[4’,5’]imidazo[2’,1’:6,1]pyrido[2,3-d]pyrimidines: Past and Present

Synthetic approaches to the construction of the heterocyclic benzo[4’,5’]imidazo[2’,1’:6,1]pyrido[2,3-d]pyrimidine system based on heterocyclizations of substituted benzimidazoles and a new alternative strategy based on 2,4,6-trisubstituted pyrimidinyl-5-propanoic acids are considered. The latter method has been shown to be a successful addition to previously described methods, since it allows one to bypass the significant limitations associated with the use of substituted benzimidazoles and allows the introduction of functional substituents at different positions of the heterocycle that are inaccessible by other methods. The available information on derivatives of this heterocyclic system and their biological properties is summarized.

Polybenzimidazoles containing heterocyclic benzo[c]cinnoline structure prepared by sol-gel process and acid doping level adjustment for high temperature PEMFC application

Polybenzimidazoles containing heterocyclic benzo[c]cinnoline structure are synthesized from 3,8-benzo[c]cinnoline dicarboxylic acid, terephthalic acid and 3,3′-diaminobenzidine. Their membranes are prepared by sol-gel process, involving the conversion of polymer solution in polyphosphoric acid to phosphoric acid. The acid doping levels of the as-prepared membranes increase as the contents of benzo[c]cinnoline increase, indicating good interaction between phosphoric acid and benzo[c]cinnoline structure. The as-prepared membranes with high acid doping levels might lead to the dissolution of membranes in phosphoric acid at temperature higher than 120 °C. A new method is proposed to adjust acid doping levels by immersing the as-prepared membranes in diluted phosphoric acid solutions of various concentrations. The adjusted membranes (acid doping levels around 30 PA RU−1) exhibit enhanced mechanical properties with tensile strength in the range of 4.1–5.2 MPa. The proton conductivity of adjusted membranes maintain at 0.15–0.17 S cm−1 at 160 °C under ambient atmosphere without humidification. The single cells based on the adjusted membranes exhibit open circuit voltages and peak power densities from 0.89 to 0.91 V and 691–1253 mW cm−2 at 160 °C, respectively. Compared to other polybenzimidazole membranes prepared by sol-gel process, the adjusted polybenzimidazoles show higher mechanical strength and better single cell performance.

Facile synthesis of annulated heterocyclic benzo[kl]acridine derivatives via one-pot N–H/C–H coupling

A facile and efficient synthesis of benzo[kl]acridines was developed based on a domino reaction via a combinatorial catalyst approach.

Heavy Atom Analogues of 1,2,3-Dithiazolylium Salts: Preparation, Structures and Redox Chemistry

Synthetic routes to salts of the benzo[1,2,3]thiatellurazolylium cation [2c](+) and its selenium analogue [2b](+) are described. Access to the cation frameworks involves the intermediacy of N,N,S-trisilylated 2-aminobenzenethiol. The latter reacts smoothly with selenium and tellurium halides ECl4 (E = Se, Te) to afford the desired heterocyclic benzo cations [2b](+) and [2c](+) as their chloride salts. Anion exchange provides the corresponding GaCl4(-), OTf(-) and TeCl5(-) salts of [2c](+), all of which have been characterized by X-ray crystallography. While the gallate salts of the sulfur and selenium cations [2a](+) and [2b](+) crystallize as ion-paired cations and anions, salts of [2c](+) adopt solid-state structures that display strong association of the cations via short intermolecular Te-N' bonds. However, crystallization of [2c](+) salts in dichloroethane in the presence of GaCl3 leads to cleavage of the dimers and the formation of a Lewis acid adduct at nitrogen. Reduction of the benzo cations [2a,b](+) affords the respective radicals 2a,b, both of which have been characterized by electron paramagnetic resonance (EPR) spectroscopy. Attempts to generate the corresponding radical 2c have been unsuccessful, although a material of nominally correct elemental composition can be generated by chemical reduction. The energetics of association of [2a,b,c](+) in solution has been probed by means of density functional theory calculations using the polarized continuum model. The results suggest that the dimeric nature of the Te-centered cation is retained in solution. The strength of the interaction is, however, less than in N-alkylated tellurodiazolylium salts.

Assignment of the NMR spectra of benzo[b]triphenyleno[1,2‐d]thiophene through the application of zero quantum proton—proton correlation combined with proton‐detected long‐range multiple quantum heteronuclear chemical shift correlation

AbstractAssignment of the congested proton and carbon NMR spectra of heterocyclic benzo[b]triphenyleno[1,2‐d]thiophene was accomplished through the concerted application of several two‐dimensional NMR experiments. The inherent insensitivity of homonuclear zero quantum coherence to magnetic field inhomogeneity was used to advantage in disentangling the heavily overlapped proton NMR spectrum. Direct heteronuclear pairings were established using heteronuclear correlation with broad band homonuclear vicinal proton decoupling. Limited sample availability and solubility precluded complete establishment of long‐range heteronuclear correlations by conventional means. Proton‐detected long‐range heteronuclear multiple quantum coherence did, however, provide sufficient long‐range heteronuclear correlations to complete the assignment.A comparison of the data obtained from COSY and zero quantum experiments is presented; the ability of each to establish proton connectivities is discussed. Sensitivity limitations inherent in the conventional long‐range optimized heteronuclear chemical shift correlation experiment are contrasted with the advantages of the proton‐detected long‐range heteronuclear multiple quantum correlation experiment. Practical limitations of the latter are considered.