Novel pyrrole C-nucleosides by nitrogen extrusion from pyridazine C-nucleosides

Pyridazine C-nucleosides have been synthesized by [4+2] cycloaddition of alkynyl C-nucleosides with substituted tetrazines. These pyridazines on extrusion of a nitrogen atom afforded novel pyrrole C-nucleosides with good yields. The results of electrochemical and chemical reduction are compared.     

Anomalous transition to turbulence in inert gases

It is found experimentally that the critical Reynolds numbers for the transition to turbulence are different for He, Ar, and Kr flows. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 557–559 (10 October 1998)     

Synthesis and electronic properties of alternating alpha,alpha'-thiophene-phosphole oligomers

[structure: see text] Alternating thiophene-phosphole oligomers up to seven rings in length have been synthesized. A regular decrease of the HOMO-LUMO gap is observed upon increasing the length of the pi-conjugated system. The nature of the P-moieties dramatically influences the optical and electrochemical properties of these phosphole-based oligomers. Electro-oxidation of derivative 5a afforded an electroactive polymer exhibiting reversible p-doping.     

Azido/tetrazole equilibrium in the thiazoloacridinone series

Compounds 2-azido-6H-thiazolo[5,4-a]acridin-11-one 3 and 2-azido-6-butylthiazolo[5,4-a]acridin-11-one 4 have been prepared for the first time. The azido/tetrazole equilibria of the most soluble compound 4 has been studied in six solvents. The resulting tautomeric equilibrium constants have been compared with those of 2-azido-4,5-dimethylthiazole 1 and 2-azidobenzothiazole 2 . The rather insoluble NH derivative 3 when dissolved in DMSO contains 66% of tetrazole 3b while the corresponding anion (obtained by adding sodium hydride) is all in the tetrazole 13b form.     

Synthetic applications of the nickel-catalyzed cyclization of alkynes combined with addition reactions in a domino process

Carbonickelations of alkynes and functionalization of the resulting vinylnickel moiety have been performed efficiently in a nickel-catalyzed domino cyclization-condensation process. This reaction, which does not require the preparation of any other organometallic reagent, proceeds only by exo-dig cyclization. This convenient and mild method constitutes a one-pot synthesis of substituted dihydrobenzofurans, chromans, isochromans, indoles, or indanes. Theses valuable products are generally obtained in good yields and high stereoselectivity. They are shown to be useful synthons for rapid access to functionalized polycyclic skeletons.     

Natural source compatibilizers for olive waste/recycled polypropylene matrix composites

A simple, environmentally friendly process was developed for surface hydrophobization of cellulose-rich waste to improve their compatibility with recycled polypropylene (rPP), helping reduce costs while recycling environmentally problematic waste such as solid olive waste (also called olive pomace). In this study, an improvement of the interfacial bonding strength between the hydrophilic waste particles and the hydrophobic matrix was achieved by surface hydrophobization of the waste using a ring-opening polymerization reaction of epoxidized soy-bean oil (ESBO) with SnCl₂ as a catalyst. The treatment on cellulose based filter paper led to a contact angle of 128°. The composite containing treated olive pomace has shown an increase in the elongation of 92% and an increase in the stress at yield of 15%, indicating improved compatibility.     

Tetrazo[1,2-b]indazoles: Straightforward Access to Nitrogen-Rich Polyaromatics from s-Tetrazines

The straightforward access to a new class of aza-polyaromatics is reported. Starting from readily available fluorinated s-tetrazine, a cyclization process with azide leads to the formation of an unprecedented tetrazo[1,2-b]indazole or a bis-tetrazo[1,2-b]indazole (cis and trans conformers). Based on the new nitrogen core, further N-directed palladium-catalyzed ortho-C−H bond functionalization allows the introduction of halides or acetates. The physicochemical properties of these compounds were studied by a joint experimental/theoretical approach. The tetrazo[1,2-b]indazoles display solid-state π-stacking, low reduction potential, absorption in the visible range up to the near-infrared, and intense fluorescence, depending on the molecular structure.     

Molecular simulation of the interlayer structure and the mobility of alkyl chains in HDTMA+/montmorillonite hybrids

Molecular simulation techniques are used to find the basal spacing of organoclay on the basis of the energy minimum, using the canonical NVT ensemble. Then, the interlayer structure and mobility of alkyl chains are explored based on the interlayer atomic density profiles. Besides the basic lateral-monolayer arrangement, lateral-bilayer accompanied by partial a pseudo-trilayer and a transition structure between the two basic lateral models are observed. The later provides an excellent explanation about the reflection at 16 angstroms on XRD patterns in the literature. The atomic density profiles reveal that nitrogen atoms show stronger layering behavior than carbon atoms do. Our simulation demonstrates that the molecular mobility of the confined alkyl chains decreases from lateral-monolayer to lateral-bilayer with the increase of the intercalated surfactant. This is in accordance with the suggestion deduced from experiments. Furthermore, our simulation indicates that the mobility of the alkyl chains strongly depends on the surfactant arrangement rather than the surfactant packing density.     

Tautomerism and 1H, 13C and 15N NMR spectral assignments of some nitro derivatives of malonic acid diamide

Because of its reactivity, malonic acid diamide (1) was initially identified as an alternative precursor for the development of a new class of high-density insensitive energetic materials possessing low sensitivity to thermal decomposition and detonation by impact. Nitration of 1 was studied under different conditions and led to three different tautomeric forms (2-4) of nitromalonic acid diamine. Using stronger oxidation conditions the oxadiazole 5 was generated in one step. We report the full 1H, 13C and 15N NMR structural characterization of these compounds in DMSO together with thermal, infrared, mass spectrometric and x-ray analysis. Experimental data obtained for 4 are compatible with an enol-imine form. Our interpretation is consistent with calculated 1H and 13C NMR spectra (ACD).