Intramolecular Metal-Free N-N Bond Formation with Heteroaromatic Amines: Mild Access to Fused-Triazapentalene Derivatives.

Formation of N-N bonds may offer an original approach to various nitrogen-containing heterocycles with numerous applications. For this purpose, we found that readily available heteroaromatic amines are appropriate substrates for providing an efficient and innovative approach for the formation of N-N bonds in the presence of iodine (III) reagent in very mild conditions. This method makes it possible to synthesize nitrogen rich triazapentalene derivatives exhibiting fluorescent properties, inaccessible with existing approaches.

Efficient sensing of explosives by using fluorescent nonporous films of oligophenyleneethynylene derivatives thanks to optimal structure orientation and exciton migration.

The fluorescence of thin films of a diimine-substituted phenyleneethynylene compound can be efficiently quenched by nitroaromatic vapors, which is not the case for the unsubstituted parent compound. Thin-film porosity is usually considered to be an essential factor for efficient quenching, but in the present case the origin of the quenching is completely different, as both films are nonporous and hermetic to 2,4-dinitrotoluene (DNT) molecules. The molecular organization in the two crystallized thin films offers a low level of π stacking for both compounds, but the orientation of the phenylenethynylene fluorophore differs markedly with respect to the surface of the films. For the substituted compound, the fluorophore is almost parallel to the surface, thus making it readily available to molecules of a nitroaromatic quencher. This rationale is also observed in the case of a related compound bearing methoxy side chains instead of the long octyloxy moieties. Fluorescence-lifetime experiments show that the efficient quenching process in the nonporous crystallized films of the substituted compound is due to a fast (<70 ps) diffusion of excitons from the bulk of the film toward the surface where they are quenched, thus providing evidence of antenna effects.

Ability of various materials to detect explosive vapors by fluorescent technologies: a comparative study.

For the development of fluorescent sensors, one of the key points is choosing the sensitive material. In this article, we aim at evaluating, under strictly identical experimental conditions, the performance of three materials for the detection of dinitrotoluene (a volatile marker of trinitrotoluene) through different parameters: response time, fluorescence intensity, sensitivity, reversibility, reaction after successive exposures and long-term stability. The results are discussed according to the nature of the sensitive materials. This first study rendered it possible to select a conjugated molecule as the best sensitive material for the development of a lab-made prototype. In a second part, the selectivity of this particular sensitive material was studied and its ability to detect TNT could be demonstrated.

Comparison of fluorescence and QCM technologies: example of explosives detection with a pi-conjugated thin film.

A pi-conjugated compound was synthesized as a sensitive material for explosives detection. The detection of vapors of 2,4-dinitrotoluene was demonstrated with quartz crystal microbalance (QCM) and fluorescence transduction methods. The fluorescence intensity monitoring shows a higher sensitivity and selectivity than the monitoring of the QCM frequency. Both methods appear to be synergic when used simultaneously as the sensor helps to discriminate interferent vapors from nitroaromatics.

(1)H, (13)C and (15)N NMR spectral assignments for new triazapentalene derivatives.

Mesomeric heteropentalene betaines are conjugated fused polyheterocyclic structures that represent interesting intermediates for organic synthesis. Five such structures, containing at least four nitrogen atoms and various substituents, have been characterized by (1)H, (13)C and (15)N NMR. We report, apparently for the first time, nitrogen NMR data and coupling information on such systems. Inter-ring long-range correlations across five bonds with (15)N ((5)J(HN)) and up to seven bonds with (13)C ((6)J(HC) and (7)J(HC)) were observed in HSQC experiments. The incorporation of an electron-withdrawing substituent such as NO(2) was observed to cause an increase in the magnitude of the remote couplings and deshielding of nearby protons, carbons and on all nitrogen atoms of the structure, including remote ones situated on other cycles.

Spectral assignments for 1H, 13C and 15N solution and solid-state NMR spectra of s-tetrazine and dihydro-s-tetrazine derivatives.

Tetrazine-based organic species are interesting intermediates for organic synthesis and represent a source of new materials bearing specific properties with potential applications in biology and material science. 1H, 13C, 15N NMR measurements carried out in solution and in the solid-state have been used to characterize a series of 3,6-disubstituted 1,2,4,5-tetrazine/dihydrotetrazine new derivatives. Experimental results presented here provide data for the assignment of 15N chemical shifts including new organic small molecules; two polymers having the tetrazine ring in the main chain and several previously published compounds. We report apparently for the first time 15N experimental chemical shift data for tetrazine systems in the solid state.

Easy access to 3- or 5-heteroarylamino-1,2,4-triazines by S(N)Ar, S(N)H, and palladium-catalyzed N-heteroarylations.

In this paper, N-arylations between two heteroaryl compounds were studied. Conditions were found to generate selectively either 3- or 5-heteroarylamino-1,2,4-triazines by investigating anionic processes (use of bases such as 2,2',6,6'-tetramethylpiperidine/tBuOK/nBuLi) or Pd-catalyzed N-arylations [Pd(OAc)(2), xantphos]. These methods were successfully applied to a wide variety of heteroarylamines and allowed us to pursue our work on fused polynitrogen compounds synthesis.

Highly diastereoselective synthesis of C6-functionalized dihydroimidazotriazines.

[reaction: see text] The first examples of C(6)-substituted 7-hydroxy-6,7-dihydro-5H-imidazo[1,2-b][1,2,4]triazines have been prepared by ring closure of different 5(2H)-1,2,4-triazin-3-ones 1a-c with 40% aqueous glyoxal and various nucleophiles (alcohols, thiols, or amines). The structure and exact stereochemistry of 2a was established by a single X-ray diffraction study and (1)H and (13)C NMR spectra analysis. The process was shown to be totally regio- and diastereoselective. A mechanism involving an imine intermediate was proposed.