First and Efficient Method for Reduction of Aliphatic and Aromatic Nitro Compounds with Zinc Borohydride as Pyridine Zinc Tetrahydroborato Complex: A New Stable Ligand‐Metal Borohydride

Pyridine zinc tetrahydroborate, [(Py)Zn(BH₄)₂], as a new stable ligand‐metal borohydride, is prepared quantitatively by complexation of 1:1 zinc borohydride and pyridine at room temperature. This reagent efficiently reduces different aromatic and aliphatic nitro compounds to their primary amines in refluxing THF. In addition, the reduction shows chemoselectivity for aliphatic nitro compounds over the aromatic nitro compounds.     

Allylation of Carbonyl Compounds Mediated by Aluminum/Fluoride Salts in Water

A novel mediator (Al/KF) has been developed and employed in the Barbier‐type alkylations of various aldehydes and ketones with alkyl halide in water. The carbonyl compounds could be effectively converted into corresponding homoallylic alcohol in good yields only when allyl bromides or substituted allyl bromides were used as halides. Aromatic aldehydes could afford homoallylic alcohols in high yields, unfortunately, the allylation of aromatic aldehyde substituted by nitro‐ or amino‐group could not proceed smoothly, and the allylation yields of ketones and aliphatic carbonyl compounds were lower under the same condition. The diastereoselectivity and regioseletivity of the reaction have also been studied, the predominant products preferred the erythro‐ or anti‐isomer in dominant γ‐adduct by using Al/KF mediated allylation of benzaldehydes with cinnamyl bromide and ethyl 4‐bromo‐2‐butenoate in water.     

Alkali hydrolysis of trinitrotoluene

Data for alkali hydrolysis of 2,4,6-trinitrotoluene (TNT) in aqueous solution at pH 12.0 under static (pH-controlled) as well as dynamic (pH-uncontrolled) conditions are reported. The experiments were conducted at two different molar ratios of TNT to hydroxyl ions at room temperature. The TNT disappeared rapidly from the solution as a first-order reaction. The complete disappearance of aromatic structure from the aqueous solution within 24 h was confirmed by the ultraviolet-visible (UV-VIS) spectra of the samples. Cuvet experiments in a UV-VIS spectrophotometer demonstrated the formation of Meisenheimer complex, which slowly disappeared via formation of aromatic compounds with fewer nitro groups. The known metabolites of TNT were found to accumulate only in very small quantities in the liquid phase.     

Selective and Sensitive Aqueous‐Phase Detection of 2,4,6‐Trinitrophenol (TNP) by an Amine‐Functionalized Metal–Organic Framework

Highly selective and sensitive aqueous‐phase detection of nitro explosive 2,4,6‐trinitrophenol (TNP) by a hydrolytically stable 3D luminescent metal–organic framework is reported. The compound senses TNP exclusively even in the presence of other nitro‐compounds, with an unprecedented sensitivity in the MOF regime by means of strategic deployment of its free amine groups. Such an accurate sensing of TNP, widely recognized as a harmful environmental contaminant in water media, establishes this new strategic approach as one of the frontiers to tackle present‐day security and health concerns in a real‐time scenario.     

One‐Pot Synthesis of Aliphatic Nitro Compounds by Michael/retro‐Claisen Fragmentation Domino Reaction

A novel and concise method for the construction of γ‐nitro ketones and 1,3‐dinitro compounds with chemoselective acyl transfer has been presented under basic conditions via one‐pot reactions. These reactions feature high atom‐ and step‐economic possess, mild condition and simple operation for one‐pot synthesis of aliphatic nitro compounds. This protocol provides the products in good yields. The possible reaction mechanism has also been proposed.     

(n‐Nitrophenyl)acetonitrile,with n = 2, 3 and 4

The molecular structures of the three title nitro‐substituted phenyl­aceto­nitriles, C₈H₆N₂O₂, at 123 K show that the mol­ecules are linked together very differently. In the 2‐ and 4‐nitro compounds, there are both O?H and N_cyano?H interactions, whereas the crystal lattice of the 3‐nitro compound is essentially built up by O?H interactions. The O atoms seem to prefer the aromatic H atoms, while the cyano N atoms prefer the methyl­ene H atoms. The phenyl–nitro torsion angles are ?19.83 (13), ?5.69 (12) and ?2.88 (12)°, while the phenyl–cyano­methyl torsion angles are ?62.27 (12), ?147.99 (9) and ?16.75 (14)° in the 2‐, 3‐ and 4‐NO₂‐substituted compounds, respectively.     

A theoretical study of the structure and vibrations of 2,4,6-trinitrotolune

Theoretical calculations of the structure, internal rotations and vibrations of 2,4,6-trinitrotolune, TNT, in the gas phase were performed at the B3LYP/6-31G* and B3LYP/6-311+G** levels of theory. Two genuine energy minimum structures were found. In both structures the 4-nitro group is planar to the phenyl ring, while the 2,6-nitro groups are slightly out of plane with the phenyl ring due to steric interaction with the methyl group. The two structures are related by internal rotations of the methyl and 2, or 6-nitro group. The lowest energy route for interconversion between them is a concerted motion of the methyl group and 2 or 6 nitro group in a ‘cog wheel’ type of mechanism. The geometry of the low energy structure A is closest to that observed in the crystal structures of TNT, where all three nitro groups are out of plane with the phenyl ring. FTIR and Raman spectra of solid TNT and ¹³C, ¹⁵N enriched TNT are presented and assigned with the help of the B3LYP/6-311+G** calculations on A. The lower level B3LYP/6-31G* calculation fails to predict the correct vibrational coupling between the nitro and phenyl groups. The B3LYP/6-311+G** calculation gives a good prediction of the nitro vibrations and the isotopic shifts observed for TNT isotopomers.     

Silica Gel as a Promoter of Sequential Aza‐Michael/Michael Reactions of Amines and Propiolic Esters: Solvent‐ and Metal‐Free Synthesis of Polyfunctionalized Conjugated Dienes

We present an efficient, simple, metal‐ and solvent‐free silica‐gel‐promoted synthesis of functionalized conjugated dienes by sequential aza‐Michael/Michael reactions by starting from commercially available primary amines and propiolic esters. The scope and usefulness of the method is demonstrated for 31 examples, including a range of propiolic esters, aliphatic amines, and differently substituted aromatic amines. For aliphatic amines, the products were obtained within 0.5 to 4 h in 52 to 85 % yield, compared with 3.5 to 22 h under classical solution‐phase synthesis, which proceeds with similar or lower yields. The method was found to be particularly useful for weakly nucleophilic aromatic amines, which provided products in 21 to 73 % yield over 2.5 to 9.5 h compared with yields of 0 to 49 % over 1 to 6 d under standard solution‐phase conditions, and for more hydrophobic esters that gave products in yields of 47 to 79 % over 1 to 3 h compared with 0 to 45 % over 4 to 114 h in solvent.     

Can a Ketone Be More Reactive than an Aldehyde? Catalytic Asymmetric Synthesis of Substituted Tetrahydrofurans

O‐heterocycles bearing tetrasubstituted stereogenic centers are prepared via catalytic chemo‐ and enantioselective nucleophilic additions to ketoaldehydes, in which the ketone reacts preferentially over the aldehyde. Five‐ and six‐membered rings with both aromatic and aliphatic substituents, as well as an alkynyl substituent, are obtained. Moreover, 2,2,5‐trisubstituted and 2,2,5,5‐tetrasubstituted tetrahydrofurans are synthesized with excellent stereoselectivities. Additionally, the synthetic utility of the described method is demonstrated with a three‐step synthesis of the side chain of anhydroharringtonine.     

Dipyrenylcalix[4]arene—A Fluorescence‐Based Chemosensor for Trinitroaromatic Explosives

A new chemosensor‐based approach to the detection of nitroaromatics is described. It involves the analyte‐induced quenching of excimer emission of a dipyrenyl calix[4]arene ( L ). The chemical and photophysical properties of the complexes formed between L and mono‐, di‐, and trinitrobenzene, and di‐ and trinitrotoluene were studied in acetonitrile and chloroform by using ¹H NMR, UV/Vis, and fluorescence spectroscopy. Fluorescence spectroscopy revealed that the trinitroaromatics engendered the largest response among the various substrates tested, with the sensitivity for these analytes being correspondingly high. Quantitative analysis of the fluorescence titration profile generated from the titration of L with TNT provided evidence that this particular functionalized calix[4]arene receptor allows for the detection of TNT down to the low ppb level in CH₃CN. A single‐crystal X‐ray diffraction analysis revealed that in the solid state the complex L? TNT consists of a supramolecular crystalline polymeric structure, the formation of which appears to be driven by intermolecular π–π interactions between two pyrene units and a TNT molecule held at a distance of 3.2–3.6 Å, as well as by intra‐ and intermolecular hydrogen‐bonds among the amide linkages. Nevertheless, the changes in the ¹H NMR, UV/Vis, and fluorescence spectrum, including sharp color changes, are ascribed to a charge‐transfer interaction arising from complementary π–π overlap between the pyrene subunits and the bound trinitroaromatic substrates. A number of ab initio calculations were also carried out and, considered in concert, they provide further support for the proposed charge‐transfer interactions, particularly in the case of L? TNT.     

Separation of aromatic sulphonic acids by CZE in coated and non‐coated capillaries

Capillary zone electrophoresis (CZE), besides ion‐pairing mode HPLC and salting‐out HPLC, is well‐suited for the analysis of aromatic sulphonic acids widely used as intermediates in the production of synthetic dyes and optical brighteners. The separation selectivity in CZE of many aromatic acids, including positional isomers, can be controlled by the type and concentration of a cyclodextrin additive. The influence of the concentration of β‐cyclodextrin in the working electrolyte on the separation of the positional isomers of naphthalene (poly‐)sulphonic acids, and their amino‐ and hydroxy derivatives, by CZE was studied, both in non‐coated fused silica capillaries and in capillaries coated with polyacrylamide. The migration time scale was calibrated using 4‐alkylbenzenesulphonic acids as the calibration standards. Limiting mobilities of the free acid anions and of their complexes with β‐cyclodextrin were calculated and the effect of the inclusion guest‐host complex formation on the CZE separation was quantitatively characterized. The migration order in coated capillaries is reversed with respect to CZE in non‐coated fused silica capillaries, the separation selectivity is different and the separation of polysulphonic acids such as naphthalene tri‐ and tetrasulphonic acids is significantly accelerated.     

Fe‐enriched Clay‐coated and Reduced Graphene Oxide‐modified N‐doped Polymer Nanocomposite: A Natural Recognition Element‐based Sensing Electrode for DNT

Dinitrotoluene (DNT) is a signature material of all nitro‐aromatic explosives including the lethal 2,4,6‐trinitrotoluene (TNT). A clay‐modified reduced graphene oxide (rGO)‐polymer nanocomposite was prepared as sensing electrode for the detection of (DNT) in the aquatic systems. rGO was in situ dispersed in the electro‐conductive N‐doped phenol/formaldehyde polymer and the clay ‘montmorillonite’ was coated on the nanocomposite. The clay, containing iron as one of its mineral components, served as the recognition element for DNT. Tested using electrochemical measurement techniques – cyclic voltammetry and differential pulse voltammetry, the prepared sensing electrode exhibited a low detection limit (0.0016 μM) on signal to noise ratio basis (S/N=3) and excellent linearity (R²=0.997) over 0.02–10 mg L^?1 with high sensitivity value (428 μA mM^?1 cm^?2) for DNT. The electrode showed negligible interference with the gravimetric and volumetric salts commonly present in seawater, and also, with explosive derivatives. The separate tests performed in a simulated seawater confirmed the suitability of the prepared electrode for use in field applications.     

Effects of Side Arm Length and Structure of Para-Substituted Phenyl Derivatives on Their Binding to the Host Cyclobis(paraquat-p-phenylene)

The binding constants with the host cyclobis(paraquat-p-phenylene), 1(4+), have been determined in CH(3)CN by UV-vis spectrophotometry for a series of p-phenylene guests, symmetrically substituted with side arms of varying length and functionality. Semiempirical molecular orbital theory was employed to provide a detailed structural and energetic interpretation of the experimental binding data. In particular, the length of the side arms and the type and position of the heteroatoms on the side arms were systematically varied in order to understand the effects of external interactions on the association constants of the guests with host 1(4+). A large chelate effect involving the ethyleneoxy side arm oxygen atoms and a cooperative effect between the guest aromatic core and the side arms are significant factors which determine the binding with this host. Sequential ethyleneoxy linkages along the side arms markedly increase the binding constant with respect to a compound in which the same number of oxygens along the side arms are separated by longer aliphatic linkages. In addition, a multiplicative rather than additive effect on the binding constant is observed which demonstrates that the oxygen atoms exhibit a strong chelate effect. It was also discovered that while the side arms of these guests contribute most of the driving force for complexation, an aromatic core is necessary for the guest to reside in the cavity of the host. The binding of these guests then is dependent upon cooperation between the arms and the aromatic core. Furthermore, elongation of the central aromatic core with aliphatic side arms containing no heteroatoms leaves the association constant relatively unchanged and replacement of the oxygen atoms with sulfur markedly decreases the observed binding. These effects have been used to rationalize several observations regarding this system in the literature and may serve to improve the design of new supramolecular systems and to better understand the host/guest interaction process.     

Reductive Molybdenum‐Catalyzed Direct Amination of Boronic Acids with Nitro Compounds

The synthesis of aromatic amines is of utmost importance in a wide range of chemical contexts. We report a direct amination of boronic acids with nitro compounds to yield (hetero)aryl amines. The novel combination of a dioxomolybdenum(VI) catalyst and triphenylphosphine as inexpensive reductant has revealed to be decisive to achieve this new C?N coupling. Our methodology has proven to be scalable, air and moisture tolerant, highly chemoselective and engages both aliphatic and aromatic nitro compounds. Moreover, this general and step‐economical synthesis of aromatic secondary amines showcases orthogonality to other aromatic amine syntheses as it tolerates aryl halides and carbonyl compounds.     

Multinuclear enantiopure titanium self‐assembly complexes—synthesis,characterization and application to organic synthesis

Hexa‐ and nonanuclear titanium complexes were obtained by self‐assembly of titanium(IV)‐tert‐butoxide and D ‐mandelic acid. Suitable single crystals of these complexes were characterized by X‐ray structure analysis. When used with these complexes, aldol adducts were isolated with a high degree of regioselectivity in direct aldol additions of aromatic and aliphatic aldehydes to functionalized unsymmetrical ketones. High syn‐diastereoselectivities were obtained in aldol additions of enolizable aldehydes with hydroxyacetone and methoxyacetone. Copyright © 2007 John Wiley & Sons, Ltd.     

Role of Intramolecular Aromatic π–π Interactions in the Self‐Assembly of Di‐l‐Phenylalanine Dipeptide Driven by Intermolecular Interactions: Effect of Alanine Substitution

Although the role of intermolecular aromatic π–π interactions in the self‐assembly of di‐l ‐phenylalanine (l ‐Phe‐l ‐Phe, FF), a peptide that is known for hierarchical structure, is well established, the influence of intramolecular π–π interactions on the morphology of the self‐assembled structure of FF has not been studied. Herein, the role of intramolecular aromatic π–π interactions is investigated for FF and analogous alanine (Ala)‐containing dipeptides, namely, l ‐Phe‐l ‐Ala (FA) and l ‐Ala‐l ‐Phe (AF). The results reveal that these dipeptides not only form self‐assemblies, but also exhibit remarkable differences in structural morphology. The morphological differences between FF and the analogues indicate the importance of intramolecular π–π interactions, and the structural difference between FA and AF demonstrates the crucial role of the nature of intramolecular side‐chain interactions (aromatic–aliphatic or aliphatic–aromatic), in addition to intermolecular interactions, in deciding the final morphology of the self‐assembled structure. The current results emphasise that intramolecular aromatic π–π interaction may not be essential to induce self‐assembly in smaller peptides, and π (aromatic)–alkyl or alkyl–π (aromatic) interactions may be sufficient. This work also illustrates the versatility of aromatic and a combination of aromatic and aliphatic residues in dipeptides in the formation of structurally diverse self‐assembled structures.     

O2‐Mediated Oxidation of Aminoboranes through 1,2‐N Migration

In analogy to the classical reaction of C?B bonds with peroxides, the first oxidative functionalization of aminoboranes through a 1,2‐N migration was realized. Readily available aliphatic nitro compounds are thereby transformed into N‐ and O‐functionalized hydroxylamines in a single synthetic operation. Addition of hazardous peroxides is avoided. Instead, the insertion of O₂, as the terminal oxidant, into Zn?C bonds provides the necessary peroxides. The required zinc organyls, in turn, are formed through a boron‐to‐zinc exchange, from an organoboronic ester byproduct of the nitro‐to‐aminoborane transformation.     

Stereoselective Access to γ‐Nitro Carboxylates,Precursors for Highly Functionalized γ‐Lactams

A straightforward synthesis of the enantiomerically pure nitro derivatives 31 and epi‐ 32 , which are particularly useful intermediates for the synthesis of highly functionalized γ‐lactams, is presented. (+)‐(R)‐3‐Hydroxy‐3‐phenylpropanoic acid ( 20 ) and its ethyl ester 25 were prepared from (+)‐L ‐mandelic acid ( 21 ). Condensation of 20 with pivalaldehyde furnished the novel enantiomerically pure 1,3‐dioxan‐4‐one 17 , the absolute configuration of which was established by X‐ray crystal‐structure analysis. Treating the lithium enolate of 17 with the nitro alkene 18 led, in a Michael‐type addition, to a 1 : 1 mixture of two diastereoisomeric products. The stereocontrol of the addition was limited to the novel stereogenic center next to the lactone function. When the lithium enolate of 25 was treated with 18 , the same selectivity was observed but with a lower chemical yield. Very facile separation of the isomers was achieved later in the synthetic sequence, when one isomer cyclized selectively to the nitro lactone 31 , while the other one was isolated as hydroxy ester epi‐ 32 . The relative configuration of racemic epi‐ 32 could be established by X‐ray crystal‐structure analysis.     

Inverted Opal Fluorescent Film Chemosensor for the Detection of Explosive Nitroaromatic Vapors through Fluorescence Resonance Energy Transfer

This paper reports an inverted opal fluorescence chemosensor for the ultrasensitive detection of explosive nitroaromatic vapors through resonance‐energy‐transfer‐amplified fluorescence quenching. The inverted opal silica film with amino ligands was first fabricated by the acid–base interaction between 3‐aminopropyltriethoxysilane and surface sulfonic groups on polystyrene microsphere templates. The fluorescent dye was then chemically anchored onto the interconnected porous surface to form a hybrid monolayer of amino ligands and dye molecules. The amino ligands can efficiently capture vapor molecules of nitroaromatics such as 2,4,6‐trinitrotoluene (TNT) through the charge‐transfer complexing interaction between electron‐rich amino ligands and electron‐deficient aromatic rings. Meanwhile, the resultant TNT–amine complexes can strongly suppress the fluorescence emission of the chosen dye by the fluorescent resonance energy transfer (FRET) from the dye donor to the irradiative TNT–amino acceptor through intermolecular polar–polar resonance at spatial proximity. The quenching response of the highly ordered porous films with TNT is greatly amplified by at least 10‐fold that of the amorphous silica films, due to the interconnected porous structure and large surface‐to‐volume ratio. The inverted opal film with a stable fluorescence brightness and strong analyte affinity has lead to an ultrasensitive detection of several ppb of TNT vapor in air.     

Electrochemical study of methylene blue/titanate nanotubes nanocomposite and its layer-by-layer assembly multilayer films

Titanate nanotubes (TNT) were proven to be efficient support for the immobilization of methylene blue (MB). UV–vis absorption and Fourier transform infrared spectra showed that the effect of MB absorbed on TNT was better than nanocrystalline anatase TiO₂ (TNP). The quantity of MB absorbed onto TNT was found to be greater than that of TNP and the electrode modified with the MB–TNT film was more stable due to the strong interaction between TNT and MB as well. The absorption of MB on TNT was impacted by the pH value of the reaction solution for the change of surface charge. Electrochemical oxidation of dopamine (DA) at different electrodes was studied. The result showed that the MB–TNT composite film exhibited excellent catalytic activities to DA compared to those of pure TNT, which is a result of the great promotion of the electron-transfer rate between DA and the electrode surface by the MB–TNT film. Furthermore, the layer-by-layer self-assembly behavior of the electrochemically functional MB–TNT nanocomposite was also discussed after obtaining the stable colloid suspension of MB–TNT. The excellent electrochemical ability and the easy fabrication of layered nanocomposite make the MB–TNT nanocomposite very promising in electrochemistry study and new nanotube-based devices.