Tetrabromo Derivatives Research Articles

Charging a Negatively Curved Nanographene and Its Covalent Network.

This study explores a bottom-up approach toward negatively curved carbon allotropes from octabenzo[8]circulene, a negatively curved nanographene. Stepwise chemical reduction reactions of octabenzo[8]circulene with alkali metals lead to a unique highly reduced hydrocarbon pentaanion, which is revealed by X-ray crystallography suggesting a local view for the reduction and alkali metal intercalation processes of negatively curved carbon allotropes. Polymerization of the tetrabromo derivative of octabenzo[8]circulene by the nickel-mediated Yamamoto coupling reaction results in a new type of porous carbon-rich material, which consists of a covalent network of negatively curved nanographenes. It has a specific surface area of 732 m2 g-1 and functions as anode material for lithium ion batteries exhibiting a maximum capacity of 830 mAh·g-1 at a current density of 100 mA·g-1. These results indicate that this covalent network presents the key structural and functional features of negatively curved carbon allotropes.

A 1,2-Dibromosilene: Generation, Spectroscopic Observation, and Isomerization to a Silacyclohexane via Facile 1,2-Bromine Shift

1,2-Dihalosilene is a hitherto unknown but potentially useful functionalizable compound for new silenes and silicon–carbon triply bonded species. We successfully generate 1,2-dibromosilene 1 by the reaction of tetrabromo derivative 2 with BuLi. The formation of 1 is confirmed by NMR studies and trapping experiments. Silene 1 survives under −80 °C, but 1 thermally isomerizes to silacyclohexane 6 via a 1,2-bromine shift to form bis(silyl)carbene 11 and the subsequent intramolecular C–H insertion.

Mass spectrometric study of the bromination of technical mixtures of polychlorinated biphenyls

The products of bromination of polychlorinated biphenyls (PCBs) that constitute Trichlorobiphenyl and Sovol PCB technical mixtures were studied by gas chromatography–mass spectrometry. On the basis of mass spectrometric data, the reaction was shown to result in formation of a mixture of poly(bromochloro)biphenyls containing from one to five bromine atoms and from two to six chlorine atoms in different combinations. It was found that the content of monobromo derivatives increases while the content of di-, tri-, and tetrabromo PCB derivatives decreases when the chlorination degree of the initial PCBs increases.

SYNTHESIS OF 8-HYDROXYQUINOLINE CHALCONES: TRANS CONFIGURATION, INTRAMOLECULAR HYDROGEN BONDS, BROMINATION, AND ANTIFUNGAL ACTIVITY

ABSTRACT Nine (8-Hydroxyquinolin-5-yl)-arylpropenones were synthesized and their structures demonstrated by IR and NMRspectroscopy. These molecules showed transconfiguration and strong intramolecular hydrogen bonding; in the IR spectra of 5-formyl-8-hydroxyquinoline, 5-acetyl-8-hydroxyquinoline, 1-(8-hydroxyquinolin-5-yl)-3-phenylprop-2-en-1-one and 3-(8-hydroxyquinolin-5-yl)-1-phenylprop-2-en-1-one in CHCl 3 , besides the known intermolecular hydrogen band (~3180 сm -1 ), we identified the intramolecular hydrogen band ОН ... N (3460 сm -1 ); the hydrogen bond peaks shifted to low frequency in proton-donor solutions such as phenol and acetic acid (with respect to 8-hydroxyquinoline) and the bonds were broken in trifluoroacetic acid solutions, due to OH protonation; the apolar solvent CCl 4 and electrophilic substituents in position 5 in the quinoline ring, limited the formation of the intermolecular hydrogen bonds and, therefore, shifted the ~3460 сm -1 intramolecularhydrogenband to lower frequencies and made it stronger and sharper. The bromination of 3-(8-hydroxyquinolin-5-yl)-1-(4-tolyl) prop-2-en-1-one occurred on the activated quinoline fragment, producing monobromo and tetrabromo derivatives, instead of bromination on the aliphatic double bond. Three chalcones tested showed strong antifungal activity

Effect of structural factors and solvent nature in bromination of anilines

Reaction of electrophilic bromination of aniline containing various ortho, meta, and para substituents in the aromatic ring was studied. The optimal conditions for synthesis of mono-, di-, tri-, and tetrabromo derivatives of aniline and brominated analog of Aniline Black were found.

A High-Spin (S = 2) Macrocycle

The nitroxide radicals in macro­cycle 2 form a quintett state (S = 2) as shown by two-dimensional pulse-based electron-spin transient nutation (2D-ESTN) spectroscopy. Compound 2 crystallizes in a 1,3-alternate conformation and was obtained from the tetrabromo derivative 1 by lithiation, reaction with (t-BuNO)2 and subsequent oxidation. The monomeric unit 4 was also prepared to study differences in the spin structures of 4 and 2.

Bromination of Alkenes and Alkynes with (Bromodimethyl)Sulfonium Bromide

Alkenes and alkynes were brominated efficiently in high yields with (bromodimethyl)sulfonium bromide in acetonitrile at room temperature. Alkenes produced the corresponding trans-dibromo compounds while alkynes (except phenylacetylene) afforded both the trans-dibromo products (major) and the tetrabromo derivatives (minor). However, phenylacetylene furnished solely the tetrabromo compound.

Synthesis of ditopic ligands containing bis(1H-pyrazol-1-yl)-methane fragments

New approaches have been proposed for the synthesis of compounds containing two bis(1H-pyrazol-1-yl)methane fragments. Nucleophilic replacement of the halogen atoms in appropriate tetrabromo derivatives by pyrazoles in the superbasic system KOH-DMSO gave ditopic chelating ligands: 1,1,2,2-tetrakis(1H-pyrazol-1-yl)ethane, 1,4-bis[bis(1H-pyrazol-1-yl)methyl]benzene, and 1,4-bis[bis(3,5-dimethyl-1H-pyrazol-1-yl)methyl]benzene. 1,4-Bis[bis(1H-pyrazol-1-yl)methyl]benzene was also synthesized by reaction of 1H-pyrazole with terephthalaldehyde in the presence of thionyl chloride. 1,1,2,2-Tetrakis(1H-pyrazol-1-yl)ethane was converted into the corresponding tetraiodo and tetranitro derivatives.

An efficient synthesis of carboxaldehyde derivatives of 4H-pyran-4-one

We developed a general method for the synthesis of various 2-mono- and 2,6-di-carboxaldehyde substituted derivatives of 3,5-diphenyl-4H-pyran-4-one and 4H-pyran-4-one. 3,5-Diphenyl-6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4a), 6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4b), 3,5-diphenyl-4-oxo-4H-pyran-2,6-dicarboxaldehyde (5a), 4-oxo-4H-pyran-2,6-dicarboxaldehyde (5b), 3,5-diphenyl-6-hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10a), and 6-hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10b) were obtained from the corresponding di-, tri-, and tetra-bromo derivatives of 2,6-dimethyl-3,5-diphenyl-4H-pyran-4-one (1a) and 2,6-dimethyl-4H-pyran-4-one (1b) by treatment with silver acetate followed by hydrolysis. Compounds 4a and 4b were also obtained by the oxidation of 10a and 10b with barium manganate.Key words: 4H-pyran-4-one, hydroxymethyl and carboxaldehyde derivatives, acetoxylation, hydrolysis, oxidation.

Crystal structure of a tetrabromo derivative of cyclopropyldihydroarglabin and its antifungal activity

A tetrabromo derivative of arglabin was synthesized stereoselectively. The molecular structure of the new compound was established using PMR and 13C NMR spectra and an x-ray structure analysis. Its antifungal activity was demonstrated.

Synthesis of novel, boron-containing cavitands derived from calix[4]resorcinarenes and their molecular recognition of biologically important polyols in Langmuir films

An efficient synthetic route for the synthesis of cavitands derived from calix[4]resorcinarene and its tetrabromo derivative was elaborated. A large-scale preparation was achieved in excellent yield, by replacing the high-boiling solvents with acetone. The tetrabromocavitands were transformed into tetra-boronic acid cavitands via lithiation with butyllithium and reaction with triethylborate. Two lipophilic cavitands bearing four boronic acid residues were demonstrated to form stable Langmuir monolayers at the water–air interface. These cavitand receptors differ in bridging unit between oxygen atoms, i.e. one contains a one-carbon unit and the other a two-carbon unit. l-sorbose, d-galactose, d-glucose, and d-cellobiose were selected for molecular recognition studies using the Langmuir techniques. The unsubstituted tetra- n-undecyl calix[4]resorcinarene was used as a reference receptor compound. Differences in surface potential were diagnostic of the different types of binding forces, which can occur.

An Ia3¯d thermotropic cubic phase from N-alkylpyridinium tetrahalocuprates

The thermotropic liquid crystalline behaviour of two N-alkylpyridinium tetrahalocuprates was investigated. The n-pentadecyl tetrachloro and tetrabromo derivatives (CU15-CL and CU15-BR, respectively) exhibit very similar behaviour on cooling, and specifically, a high temperature smectic phase followed by a cubic phase. We fully elucidated the Ia3¯d space group for the cubic phase from X-ray diffraction on single crystals. The type of cubic phase is still under discussion, but we suggest that it is a direct type of structure based on the known phase sequence of lower and higher homologues. A model for the local organization of CU15-CL and CU15-BR in the cubic and smectic mesophases is also proposed.

New Bis(chalcones) and Their Transformation into Bis(pyrazoline) and Bis(pyrazole) Derivatives

AbstractThe reaction of bis(chalcones) 1a−d and bis(chalcone) tetrabromo derivatives 3a−d with hydrazine hydrate gave bis(pyrazolines) 4a−d and bis(pyrazoles) 5a−d, respectively. Bis(pyrazoles) 5e,f bearing hydroxyphenyl substituents have been prepared from the reaction of bis(chromones) 6c,d with hydrazine hydrate, because their synthesis from the corresponding benzyloxy‐substituted 5c,d gave very poor yields. The structures of all new compounds have been established by extensive NMR spectroscopic studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis of tetrakis(2-thienyl)methane

Tetrakis(2-thienyl)methane was synthesized for the first time by sodium sulfide induced cyclization of 5,5,5-tris(2-thienyl)pentadiyne which was obtained from tris(2-thienyl)methyl cation, and the molecular structure was elucidated by X-ray analysis for the tetrabromo derivative.

Synthesis and Solid-State Structural Analysis of Exotetradentate Ligands Based on Mesitylene-Derived [1.1.1.1]Metacyclophane Fixed in a 1,3-Alternate Conformation

A series of new tetradentate ligands based on the [1.1.1.1]metacyclophane backbone fixed in a 1,3-alternate conformation was achieved. For the strategy developed, the common synthon for the preparation of twelve ligands bearing four interaction sites occupying the apices of a pseudo-tetrahedron [H, SH, CN, SCH3, CO2H, CHO, PPh2, P(O)Ph2, NO2, NH2, pyridine, and para-methoxyphenyl] was the tetrabromo derivative 7. In addition to the classical characterisation methods applied to all reported ligands, compounds 7, 9, 12, and 13 were structurally studied in the solid state by single-crystal X-ray diffraction, which indeed confirmed their 1,3-alternate conformation.

Upper rim substitution of thiacalix[4]arene

Upper rim bromination of thiacalix[4]arene has been achieved for the first time using a distally disubstituted thiacalix[4]arene as a starting material. Depending on the bromine:thiacalix[4]arene ratios, the corresponding dibromo- and tetrabromo derivatives were obtained which opens the door for subsequent derivatisation of the upper rim of thiacalix[4]arenes. Interestingly, direct bromination of tetraalkylated compounds did not yield brominated derivatives. The structure of the tetrabromo derivative in the 1,3-alternate conformation was proven by X-ray crystallography.

Ruthenium-Capping of Di- and Tetraethynylbiphenyls

The di- and tetraalkynyl biphenyls 3 and 5 have been synthesized from the tetrabromo derivative 1 by using Pd-catalyzed cross-coupling reactions. The reaction of 3 or 5 with cis-[RuCl2(dppe)2] (8) affords vinylidene ruthenium complexes, which were deprotonated with Et3N to give the terminal σ-alkynylruthenium derivatives 9−12. The reaction of 3 or 5 with [Ru(CO)ClH(PPh3)3] (13) gave the corresponding di-σ-alkenyl ruthenium complexes 14 and 15.

A comparative study of the crystal structures of tetrahalogenated hydroquinones and gamma-hydroquinone.

gamma-Hydroquinone (1) and its tetrafluoro, tetrachloro and tetrabromo derivatives (2), (3) and (4) adopt crystal structures that have an almost invariant system of O-H.O hydrogen bonds. However, within this O-H.O framework, the four structures display variations that are characteristic of the C-H, C-F, C-Cl and C-Br groups. In the parent compound (1) aromatic rings are packed with a herringbone geometry, whilst in the halogenated derivatives (3) and (4), polarization-type halogen.halogen contacts are optimized. The fluoro derivative (2) is exceptional in that neither of the above possibilities is adopted, even though the O-H.O scaffolding does not per se prohibit either of them geometrically.

A New Synthesis of Tetrakis(C-methyl)octakis(hydroxyethyl)calix[4]- resorcinarene via an Ethoxy-Tethered Trimethylsiloxy Precursor

Abstract The octakis(trimethylsiloxy)calix[4]resorcinarenes, 3 and 4, were synthesized by reaction of 1 and its tetrabromo derivative 2 with hexamethyldisilazane, and were found to exhibit dynamic behaviour in solution. Temperature-dependent NMR investigations confirmed the presence of at least two conformational isomers of 3 in solution. The conformation of 3 in the solid state was determined by an X-ray crystal structure analysis; the calixarene displays a boat conformation. The introduction of the ethoxy group as a spacer into the molecule of 1 was effected via its reaction with ethyl bromoacetate and subsequent reduction with lithium aluminium hydride forming the ethoxy-tethered C-methylcalix[4]resorcinarene 6 in an impure state. Reaction of crude 6 with hexamethyldisilazane furnished the ethoxy-tethered octakis( trimethylsiloxy)calix[4]resorcinarene 7; its hydrolysis led to pure 6.

Functionalization of the periphery of calix[4]resorcinarenes with P(III)-containing substituents via hydroxy, trimethylsiloxy, and ethoxy-tethered trimethylsiloxy intermediates

Unlike C-undecylcalix[4]resorcinarene, C-methylcalix[4]resorcinarene 1 reacted with chlorodifluorophosphine in the absence of an auxiliary base to give the unstable octakis(difluorophosphite)-substituted derivative 2. The existence of two conformational isomers of 2 in solution was observed by 19F and 31P NMR spectroscopy. Attempts to react the octakis(trimethylsilyl)calix[4]resorcinarene 3 and its tetrabromo derivative 4 with phosphorus trichloride and chlorodifluorophosphine were unsuccessful. The ethoxy-tethered C-methyl-octakis(trimeth-ylsilyl)calix[4]resorcinarene 5 was allowed to react with 2-chloro-1,3,5-trimethyl-1,3,5-triaza-2σ3λ3-phosphorin-4,6-dione and chlorodifluorophosphine. By substitution of all trimethylsilyl groups, the octakis(phosphorus(III))-substituted compounds 6 and 7 were formed. As for 2, dynamic behavior in solution was observed for 6 and 7, arising from the equilibrium between different conformational isomers. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:553–558, 1998