Five-membered Cyclic Structure Research Articles

Regioselective anti-Silyllithiation of Propargylic Amines

AbstractThe regioselective anti-silyllithiation of propargylic amines is developed to facilitate the efficient synthesis of alkenylsilanes. This reaction generates an alkenyllithium intermediate that is stabilized by the formation of a five-membered cyclic structure through intramolecular coordination of the nitrogen functional group. Upon subsequent treatment with an electrophile, the alkenyllithium intermediate is further functionalized to afford tetrasubstituted allylic amines bearing a β-silicon substituent.

Thioacyl-Transfer Ring-Expansion Polymerization of Thiiranes Based on a Cyclic Dithiocarbamate Initiator

We report the novel thioacyl-transfer ring-expansion polymerization (REP) of thiiranes, using 3H-benzothiazol-2-thione (BTT) as the cyclic dithiocarbamate initiator and tetrabutylammonium chloride (TBAC) as the catalyst. REP proceeded in a controlled manner to produce cyclic polysulfides with a narrow Mw/Mn of 1.1 and whose cyclic structures were confirmed by MALDI-TOF mass spectrometry. Time-course studies revealed unique sigmoidal profiles due to the stable five-membered cyclic structure of the BTT initiator. The GPC curves were analyzed by the Gaussian fitting method, which revealed that the cyclic polymers are accompanied by another fraction with nearly twice the molecular weight of the main product due to ring-crossover reactions between cyclic polysulfides during REP. The BTT-initiated cyclic polysulfides produced in this manner act as macroinitiators for the REP of thiiranes, highlighting the living characteristics of the BTT-initiated REP developed herein. Post-polymerization further enabled the preparation of cyclic block copolymers with different combinations of thiiranes.

Synergistic effect of size-dependent PtZn nanoparticles and zinc single-atom sites for electrochemical ozone production in neutral media

Electrochemical ozone production (EOP) via water electrolysis represents an attractive method for the generation of high-purity O 3 . Herein, the X-PtZn/Zn-N-C electrocatalysts show a strong structural sensitive behavior depends on the size of the PtZn nanoparticles and their EOP activity exhibits a volcano-type dependence for the O 3 performance in neutral media. The 7.7-PtZn/Zn-N-C exhibits EOP current efficiency of 4.2%, and shows the prominent performance in the production of gaseous O 3 with a value of 1647 ppb at 30 min, which is almost 4-fold compared to 2.2-PtZn/Zn-N-C. Based on the experiments and theoretical calculations, the performance of the EOP process was determined by the nanoparticle size-effect and the synergistic effect between the PtZn nanoparticles and atomically dispersed Zn-N-C. Furthermore, the five-membered cyclic structure of O 3 can be stabilized between the PtZn nanoparticle and the Zn-N-C support, indicating that O 3 is produced at the interface. The different sizes of PtZn dispersed on support of the Zn-N-C were successfully synthesized and exhibited a volcano-type dependence for the electrochemical ozone production (EOP) performance in neutral media.

Degradation of Adenine on the Martian Surface in the Presence of Perchlorates and Ionizing Radiation: A Reflectron Time-of-flight Mass Spectrometric Study

Abstract The aim of the present work is to unravel the radiolytic decomposition of adenine (C5H5N5) under conditions relevant to the Martian surface. Being the fundamental building block of (deoxy)ribonucleic acids, the possibility of survival of this biomolecule on the Martian surface is of primary importance to the astrobiology community. Here, neat adenine and adenine–magnesium perchlorate mixtures were prepared and irradiated with energetic electrons that simulate the secondary electrons originating from the interaction of the galactic cosmic rays with the Martian surface. Perchlorates were added to the samples since they are abundant—and therefore relevant oxidizers on the surface of Mars—and they have been previously shown to facilitate the radiolysis of organics such as glycine. The degradation of the samples were monitored in situ via Fourier transformation infrared spectroscopy and the electron ionization quadruple mass spectrometric method; temperature-programmed desorption profiles were then collected by means of the state-of-the-art single photon photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), allowing for the detection of the species subliming from the sample. The results showed that perchlorates do increase the destruction rate of adenine by opening alternative reaction channels, including the concurrent radiolysis/oxidation of the sample. This new pathway provides a plethora of different radiolysis products that were identified for the first time. These are carbon dioxide (CO2), isocyanic acid (HNCO), isocyanate (OCN−), carbon monoxide (CO), and nitrogen monoxide (NO); an oxidation product containing carbonyl groups (R1R2–C=O) with a constrained five-membered cyclic structure could also be observed. Cyanamide (H2N–C≡N) was detected in both irradiated samples as well.

Oligo(p‐phenylene‐ethynylene)s with Backbone Conformation Controlled by Competitive Intramolecular Hydrogen Bonds

A series of conjugated oligo(p-phenylene-ethynylene) (OPE) molecules with backbone conformations (that is, the relative orientations of the contained phenylene units) controlled by competitive intramolecular hydrogen bonds to be either co-planar or random were synthesised and studied. In these oligomers, carboxylate and amido substituents were attached to alternate phenylene units in the OPE backbone. These functional groups were able to form intramolecular hydrogen bonds between neighbouring phenylene units. Thereby, all phenylene units in the backbone were confined in a co-planar conformation. This planarised structure featured a more extended effective conjugation length than that of regular OPEs with phenylene units adopting random orientation due to a low rotational-energy barrier. However, if a tri(ethylene glycol) (Tg) side chain was appended to the amido group, it enabled another type of intramolecular hydrogen bond, formed by the Tg chain folding back and the contained ether oxygen atom competing with the ester carbonyl group as the hydrogen-bond acceptor. The outcome of this competition was proven to depend on the length of the alkylene linker joining the ether oxygen atom to the amido group. Specifically, if the Tg chain folded back to form a five-membered cyclic structure, this hydrogen-bonding motif was sufficiently robust to overrule the hydrogen bonds between adjacent phenylene units. Consequently, the oligomers assumed non-planar conformations. However, if the side chain formed a six-membered ring by hydrogen bonding with the amido NH group, such a motif was much less stable and yielded in the competition with the ester carbonyl group from the adjacent phenylene unit. Thus, the hydrogen bonds between the phenylene units remained, and the co-planar conformation was manifested. In our system, the hydrogen bonds formed by the back-folded Tg chain and amido NH group relied on a single oxygen atom as the hydrogen-bond acceptor. The additional oxygen atoms in the Tg chain made a negligible contribution. A bifurcated hydrogen-bond motif was unimportant. From our results, in combination with the results from an independent study by Meijer et al., it is evident that intramolecular hydrogen bonds involving back-folded oligo(ethylene glycol) moieties may differ in their structural details. Absorption spectroscopy served as a convenient yet sensitive technique for analysing hydrogen-bonding motifs in our study.

Quantum mechanical study of putative intermediates in adduct formation by the suicide substrate ethylene with cytochrome P-450

We report INDO calculations on putative intermediates in the oxidative metabolism of ethylene by cytochrome P-450 leading to either the epoxide or the formation of an adduct at the pyrrole nitrogen of the porphyrin. We also report the characterization of a ferryl model which has been postulated to be the active oxygen state involved in oxidation reactions involving cytochrome P-450. Our results suggest that adduct formation proceeds via a radical process which leaves the oxygen bound to the iron forming a five-membered cyclic structure. The possibility of an intermediate which could lead to either the epoxide or the N-alkylated porphyrin is discussed.

Participation of propargyl moiety in Butler's cyclopolymerization process

In order to investigate the possible participation of propargyl group in Butler's cyclopolymerization process, a number of quaternary ammonium chlorides containing allyl and propargyl units are prepared in excellent yields. While the monomer containing two propargyl units as the only unsaturated groups did not undergo cyclopolymerization or cyclocopolymerization with sulfur dioxide, the monomer having one allyl and one propargyl groups afforded water-soluble homo- and co-polymers. The monomer diallylmethylpropargylammonium chloride gave cross-linked homopolymers, whereas its copolymer with sulfur dioxide was found to be linear and water-soluble. Careful analysis of the 1H and 13C NMR spectra revealed for the first time the participation of the propargyl units in Butler's cyclopolymerization process to yield polymers having five-membered cyclic structure embedded in the polymer chain.

Photoelectron spectroscopy and density functional theory of puckered ring structures of Group 13 metal-ethylenediamine.

The ethylenediamine (en) complexes of Al, Ga, and In atoms were prepared in laser-vaporization supersonic molecular beams and studied with pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and density functional theory. Several conformers of each metal complex are obtained by B3LYP calculations, and a five-membered cyclic structure is identified by combining the experimental measurements and theoretical calculations. Adiabatic ionization potentials, vibrational frequencies, and bond dissociation energies are determined for the ring structure. The ionization potentials of the Al, Ga, and In species are measured to be 32 784 (5), 33 324 (5), and 33 637 (7) cm(-1), respectively, and metal-ligand dissociation energies of the ionic and neutral complexes are calculated to be 60.2/16.2 (Al(+)/Al), 55.5/13.0 (Ga(+)/Ga), and 50.0/11.4 (In(+)/In) kcal mol(-1). Metal-ligand stretch and bend as well as a number of ligand-based vibrations are measured. Harmonic frequencies and anharmonicities of the M(+)-N (M=Al,Ga,In) stretch are determined for all three M(+)-en ions and the C-C-N bend of Ga(+)-en and In(+)-en. In comparison to monodentate methylamine, the bidentate binding of ethylenediamine leads to a significantly lower ionization potential and higher metal-ligand bond strength of the metal complexes.

Synthesis and solution properties of hydrophobically associating ionic polymers made from diallylammonium salts/sulfur dioxide cyclocopolymerization

Sulfur dioxide, N, N-diallyl- N-carboethoxymethylammonium chloride and the hydrophobic monomers N, N-diallyl- N-dodecylammonium chloride or N, N-diallyl- N-octadecylammonium chloride were cyclocopolymerized in dimethyl sulfoxide using azobisisobutyronitrile (AIBN) as the initiator to afford water-soluble cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) which was converted to the anionic polyelectrolyte (APE) by treatment with sodium hydroxide. The solution properties of the CPE and APE containing varying amount of the hydrophobic monomers in the range 0–10 mol% were investigated by viscometric techniques. The polymers showed that concentration (C ∗ HA) of less than 1 wt% was required for the manifestation of hydrophobic association, and displayed significant hydrophobic association in salt (NaCl)-free as well as salt-added solutions.

Isolation and structural characterization of 1-zirconacyclopent-3-yne, five-membered cyclic alkynes.

Stable five-membered cyclic alkynes were synthesized, isolated, and fully characterized. Divalent zirconium species, bis(cyclopentadienyl)zirconium(II) equivalent, reacted with (Z)-1,4-disubstituted 1,2,3-butatrienes [(Z)-R-CH=C=C=CH-R, 1a: R = (CH3)3Si-, 1b: R = tert-C4H9-] to give 1-zirconacyclopent-3-yne compounds (2a-b) in good yields. X-ray diffraction analysis revealed their five-membered cyclic structure with a sufficiently short triple bond to regard this compound as a metallacyclopentyne.

Synthesis and solution properties of a new ionic polymer and its behavior in aqueous two-phase polymer systems

The amine salt, N,N-diallyl-N-carboethoxymethylammonium chloride was copolymerized in dimethyl sulfoxide using ammonium persulfate or azo-bis-isobutyronitrile (AIBN) to afford the cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) having the equivalent of chloride salt of N,N-diallylammonio ethanoic acid as monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB) [having the monomeric unit equivalent of sodium N,N-diallylaminoethanoate and N,N-diallylammonioethanoate] by treatment with two and one equivalent of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. Basicity constant of the amine functionality in APE is found to be ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; the protonation of the APE becomes more and more difficult as the degree of protonation (α) of the whole macromolecule increases. The composition and phase diagram of the aqueous two-phase systems of APE and poly(ethyelene glycol) (PEG) has been studied for the first time for this class of ionic polymers. The CAS and PB were found to be virtually insoluble in water.

Synthesis and solution properties of a quaternary ammonium polyelectrolyte and its corresponding polyampholyte

The quaternary ammonium salt, N, N-diallyl- N-5-carbomethoxypentyl- N-methylammonium chloride (DACPMAC), on cyclopolymerization in aqueous solution using tert-butylhydroperoxide, afforded the polyelectrolyte poly(DACPMAC), having five-membered cyclic structure on the polymeric backbone, in excellent yield. The polyelectrolyte on acidic hydrolysis of the pendent ester groups gave the corresponding polyampholyte poly(DAMAH) having the equivalent of 6-( N, N-diallyl- N-methyl ammonio) hexanoate (DAMAH) as monomeric unit. The solution properties of these polymers as well as the polyelectrolyte, poly(DACMMAC), and its corresponding polyampholyte, poly(DAMAE), [having the monomeric unit equivalent of N, N-diallyl- N-carboethoxymethyl- N-methylammonium chloride (DACMMAC) and N, N-diallyl- N-methyl ammonio ethanoate (DAMAE)] are investigated by potentiometric and viscometric techniques. Basicity constants of the polyampholytes are found to be ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation. While the protonation of the polyampholyte poly(DAMAH) becomes more and more difficult as the degree of protonation ( α) of the whole macromolecule increases, the polyampholyte poly(DAMAE), exhibits the reverse trend i.e. the protonation process becomes easier and easier with increasing α.

ESR parameters and dynamic behavior of β-phosphorylated nitroxide radicals in glycerol solution

The magnetic and dynamic properties of several β-phosphorylated nitroxide radicals in glycerol solution were studied by X-band ESR spectroscopy in the 180–380 K range. The parameters of interest were obtained from the least-squares fit of experimental spectra. These radicals display a large, weakly anisotropic 31P hyperfine coupling varying from 3 to 6 mT according to the orientation of the C(2)—P bond in the molecular frame and nearly independent of the temperature. Some of these radicals, with a five-membered cyclic structure, undergo an exchange between two conformers due to ring puckering, whose kinetics have been determined from the evolution of spectral shapes between 230 and 280 K. This motion, which modulates the 31P hyperfine coupling and leaves that of nitrogen unchanged, is hindered by substitution in position 4 of the ring of a proton by a phenyl group. All these radicals are found to undergo an anisotropic tumbling motion with correlation times decreasing from 100 to 0.1 ns between 280 and 380 K. © 1998 John Wiley & Sons, Ltd.

Epoxidation of Lower Olefins with Hydrogen Peroxide and Titanium Silicalite

The epoxidation of lower olefins, catalysed by titanium silicalite (TS-1) under mild conditions, is reported. The reaction may be performed at near room temperature, in dilute alcoholic or aqueous solutions of hydrogen peroxide. In methanol C4-C8 linear olefins, allyl chloride, and allyl alcohol show fast reaction rates and high selectivities (72-97% on H2O2). The solvolysis of the oxirane ring and the oxidation of the solvent are the main side reactions. Yields and kinetics are decreased by increasing the chain length or the cross-section of the olefin (n-Cn > n-Cn+1, 1-hexene ⪢ cyclohexene), by electron-withdrawing substituents (1-butene > allyl chloride > allyl alcohol), and by solvents in the order methanol > ethanol > t-butanol. The rate of reaction also depends on the position and steric configuration of the double bond and on the branching, as a result of inductive and shape selectivity effects: trans 2-butene < iso-butene < 1-butene < cis 2-butene, 2-methyl-1-butene < 1-pentene, and 3-methyl-1-butene < 2-methyl-1-butene < 2-methyl-2-butene. The epoxidation occurs with retention of configuration. Basic compounds at low concentration do not slow the kinetics, but do improve significantly the yields, up to 97% in the epoxidation of 1-butene. At higher concentrations, TS-1 activity is decreased and eventually inhibited by bases. No effect on kinetics is exerted by tetrapropylammonium hydroxide. Catalytic activity is improved by acids. A heterolytic peracid-like mechanism is envisaged in the oxygen-transfer step. A five-membered cyclic structure, formed by a titanium hydroperoxo moiety Ti-OOH, and a protic molecule ROH at Ti sites, is proposed as the active species.

Mechanism for chelated sulfate formation from sulfur dioxide and bis(triphenylphosphine)platinum

Structure and energy surface calculations using the atom superposition and electron delocalization molecular orbital theory show that the first step in the reaction between SO2 and the dioxygen complex (PPh3)2PtO2 is the coordination of SO2 with one oxygen atom of the complex, followed by metal-oxygen bond breaking and reorientation, leading to a five-membered cyclic structure. This then rearranges to form the bidentate coordinated sulfate. Alternative pathways are considered and are found to be less favorable.

Equilibrium structure of the molecular cation radical of ethyl acetate in the gas phase: Mechanism of formation of rearrangement ions

The equilibrium (spatial and geometric) structures of the molecular cation radical of ethyl acetate have been studied using the SCF MO LCAO method in t The molecular ion in the equilibrium state is shown to have a five-membered cyclic structure. Vertical and adiabatic ionization energies have been calc

ChemInform Abstract: RINGERWEITERUNG IN ORGANISCHEN MOLEKELN UNTER ELEKTRONENBESCHUSS, DIE MASSENSPEKTROMETRISCHE FRAGMENTIERUNG VON 2,3‐DICARBALKOXY‐SPIRO‐CYCLOPROPAN‐1,9′‐FLUORENEN

Chemischer InformationsdienstVolume 4, Issue 20 Physical Organic Chemistry ChemInform Abstract: RINGERWEITERUNG IN ORGANISCHEN MOLEKELN UNTER ELEKTRONENBESCHUSS, DIE MASSENSPEKTROMETRISCHE FRAGMENTIERUNG VON 2,3-DICARBALKOXY-SPIRO-CYCLOPROPAN-1,9′-FLUORENEN WILHELM J. RICHTER, WILHELM J. RICHTERSearch for more papers by this authorANDRE M. BRAUN, ANDRE M. BRAUNSearch for more papers by this author WILHELM J. RICHTER, WILHELM J. RICHTERSearch for more papers by this authorANDRE M. BRAUN, ANDRE M. BRAUNSearch for more papers by this author First published: May 15, 1973 https://doi.org/10.1002/chin.197320085AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume4, Issue20May 15, 1973 RelatedInformation