Multiple Bond Systems Research Articles

Radical Alkynylthiolation with Visible-Light-Sensitive S-Alkynylthio Sulfonates.

A novel kind of S-alkynylthio sulfonate, which can be directly activated under visible-light irradiation, has been developed for the radical addition of multiple bond systems and radical coupling with diazonium salts under photocatalyst-free conditions. This strategy features a broad substrate scope, high regioselectivity, excellent tolerance of functional groups, and the late-stage modification of drugs. Experimental and theoretical mechanistic investigations gave reasonable insight into the photolysis of S-alkynylthio sulfonates and C-S bond formation.

Photolysis of phosphaketenyltetrylenes with a bulky carbazolyl substituent.

Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple bond systems. We have employed the dtbpCbz substituent (dtbpCbz = 1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [(dtbpCbz)EPCO] (E = Ge, Sn, Pb). While the phosphaketenyltetrylenes are thermally very stable, they can be readily decarbonylated photolytically. For the germylene and stannylene derivative, dimeric diphosphene-type products [(dtbpCbz)EP]2 (E = Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [(dtbpCbz)PbP] intermediate to [(dtbpCbz)PPb], afforded an unsymmetric and incompletely decarbonylated product formally comprising a [(dtbpCbz)PPb] and a [(dtbpCbz)PbPCO] moiety.

Orthoamide und Iminiumsalze, IIICa. Weitere Ergebnisse bei der Umsetzung von Orthoamiden der Alkincarbonsäuren mit CH2- und CH2/NH-aciden Verbindungen

Abstract The 1,1-bis(dimethylamino)-1,3-butadienes (keten aminals) 11a–l are prepared from orthoamide derivatives of alkyne carbonxylic acids 9b, d, e, i and CH2-acidic compounds 10a–c, f–h, k, o. The C-silylated orthoamide derivative 9c shows an ambivalent behaviour towards CH-acidic compounds. Reactions of 9c with strong CH2-acidic compounds like the nitro alkanes 10m, n and strongly enolized carbonyl compounds as methyl acetoacetate, cyanoacetamide, dibenzoylmethane, 1,3-dimethylbarbituric acid proceed under desilylation to give the ketene aminals 11u–z. In contrast to these reactions, the C-silylated ketene aminals 11o–t are obtained from 9c and weaker CH2-acidic compounds as dimethyl malonate, cyanoacetic acid derivatives and benzylcyanides. CH2/NH2-acidic compounds [cyanoacetamide (10d) and N-ethyl-cyanoacetamide (10f)] react with the orthoamide derivatives 9b, e–g at the acidic carbon-hydrogen bond to give the ketene aminals 11ac, ad, af, ag, ai, which cyclize to the pyridones 14a–d, d–g on heating. From the reaction of the orthoamide 9d with cyanoacetamide the pyridone 14c results directly. The persubstituted pyridone derivative 19 is formed by the reaction of cyanoacetamide with a mixture of the isomeric orthoamides 15 and 16. The 5,5-diamino-2,4-pentadienamide 11v attacks the orthoamide 9a at C3/C1. In the product 20 a cross conjugated multiple bond system is formed which contains an 1-aza-2,3-diamino function and a further ketene aminal function.

Recent Developments in Visible-Light-Catalyzed Multicomponent Trifluoromethylation of Unsaturated Carbon–Carbon Bonds

Trifluoromethylation has emerged as an important tool for modulating the molecular chemical and physical properties in material, polymer, and medicinal chemistry. In particular, photocatalyzed trifluoromethylation in the presence of visible-light irradiation has potentially different activity under mild conditions compared with traditional methods. This review summarizes the recent advances in trifluoromethylation with multiple bond system such as alkynes and alkenes.1 Introduction2 Trifluoromethylating Reagents3 Multicomponent Reactions of Alkynes4 Multicomponent Reactions of Alkenes5 Conclusion

Electrochemical Arylation Reaction.

Arylated products are found in various fields of chemistry and represent essential entities for many applications. Therefore, the formation of this structural feature represents a central issue of contemporary organic synthesis. By the action of electricity the necessity of leaving groups, metal catalysts, stoichiometric oxidizers, or reducing agents can be omitted in part or even completely. The replacement of conventional reagents by sustainable electricity not only will be environmentally benign but also allows significant short cuts in electrochemical synthesis. In addition, this methodology can be considered as inherently safe. The current survey is organized in cathodic and anodic conversions as well as by the number of leaving groups being involved. In some electroconversions the reagents used are regenerated at the electrode, whereas in other electrotransformations free radical sequences are exploited to afford a highly sustainable process. The electrochemical formation of the aryl-substrate bond is discussed for aromatic substrates, heterocycles, other multiple bond systems, and even at saturated carbon substrates. This survey covers most of the seminal work and the advances of the past two decades in this area.

Visible Light-Mediated Installation of Halogen Functionalities into Multiple Bond Systems

Photoredox catalysis has emerged as a useful tool for organic, synthetic, and material chemists to approach target molecules with new functionalities and structural complexity. This review focuses on the recent advances in the visible light-promoted halogenation and trifluoromethylation/difluoromethylation of multiple bonds. Halogen functionalities are important chemical handles and building blocks in organic synthesis. Both electrophilic addition of halogens and radical halogenations are widely utilized in organic synthesis to install halogen functionalities. However, harsh conditions and low regioselectivity could present challenges. Despite these concerns, recent efforts have led to obvious advances in the visible light-promoted halogenation of multiple bonds. In this context, we address the recent achievements in the visible light-mediated installation of different types of halogen-containing functionalities, which include (i) halogenation of unsaturated carbon-carbon bonds, (ii) trifluoromethylation and difluoromethylation of π-systems, and (iii) photoredox cyclization by insertion of fluorine sources. A variety of active catalytic species in the photoredox halogenations are also discussed in terms of their unique reactivity for the future development of highly practical and efficient processes.

Direct Access to Inversely Polarized Phosphaalkenes from Elemental Phosphorus or Polyphosphides

AbstractPhosphorus‐containing multiple‐bond systems have received great interest in various applications but often require elaborate syntheses and special precursors. In this paper, we describe simple methods for the synthesis of imidazoyl phosphinidenes and bis(imidazolyl)–P(I) halides from elemental phosphorus or the heptaphosphides Na3P7 and (Me3Si)3P7. The reactions of imidazolium salts with KOtBu and P4 afford mixtures of imidazoyl phosphinidenes and Pn compounds and, for N‐methylated imidazolium salts, also bis(imidazolyl)–P(I) halides. NMR spectroscopy studies revealed the formation of a bis(imidazoyl)‐substituted tetraphosphatriene and the bicyclic anion HP4– as transient intermediates and indicated the participation of tBuOH in the formation of imidazoyl phosphinidenes. Na3P7 and (Me3Si)3P7 can be obtained from P4 and Pred in excellent yields by a safe and simple method and are versatile precursors for the synthesis of imidazoyl phosphinidenes with varying steric demand.

Effect of loading conditions on the dissociation behaviour of catch bond clusters

Under increasing tensile load, the lifetime of a single catch bond counterintuitively increases up to a maximum and then decreases exponentially like a slip bond. So far, the characteristics of single catch bond dissociation have been extensively studied. However, it remains unclear how a cluster of catch bonds behaves under tensile load. We perform computational analysis on the following models to examine the characteristics of clustered catch bonds: (i) clusters of catch bonds with equal load sharing, (ii) clusters of catch bonds with linear load sharing, and (iii) clusters of catch bonds in micropipette-manipulated cell detachment. We focus on the differences between the slip and catch bond clusters, identifying the critical factors for exhibiting the characteristics of catch bond mechanism for the multiple-bond system. Our computation reveals that for a multiple-bond cluster, the catch bond behaviour could only manifest itself under relatively uniform loading conditions and at certain stages of decohesion, explaining the difficulties in observing the catch bond mechanism under real biological conditions.

ChemInform Abstract: Copper‐Mediated and Copper‐Catalyzed Addition and Substitution Reactions of Extended Multiple Bond Systems

AbstractReview: 206 refs.

On the Importance of the Nature of Hydrogen Bond Donors in Multiple Hydrogen Bond Systems

AbstractAssociation constants for the reaction between a fourfold hydrogen bond receptor 4 possessing an AADA hydrogen bond pattern and several complementary partners 5–7 with DDAD and DDA patterns have been determined by NMR titration and by isothermal titration calorimetry (ITC). A variation of one donor site in the DDAD pattern resulted in the following, surprising sequence of stability of the complexes: KAss(6, X = NHCOR) > KAss(7, X = H) > KAss(5, X = NHR). The synthesis of a well soluble DDAD receptor, the amidopyridylurea 6b with a triethylene glycol chain, is described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Strength of Multiple Parallel Biological Bonds

Multivalent interactions play a critical role in a variety of biological processes on both molecular and cellular levels. We have used molecular force spectroscopy to investigate the strength of multiple parallel peptide-antibody bonds using a system that allowed us to determine the rupture forces and the number of ruptured bonds independently. In our experiments the interacting molecules were attached to the surfaces of the probe and sample of the atomic force microscope with flexible polymer tethers, and the unique mechanical signatures of the tethers determined the number of ruptured bonds. We show that the rupture forces increase with the number of interacting molecules and that the measured forces obey the predictions of a Markovian model for the strength of multiple parallel bonds. We also discuss the implications of our results to the interpretation of force spectroscopy measurements in multiple bond systems.

Pressure-induced transformations of materials: light spectroscopy investigations

Drastic changes of material properties, such as insulator-to-superconductor, are obtained by strong static compression. Striking examples are given and, depending on the starting materials, some general rules are recalled. Light spectroscopies offer convenient tools to characterise pressure-induced phase transformations. Principles of these methods are shortly recalled. Emphasis is placed on the vanishing of ferroelectricity, in perovskites and hydrogen bonded systems, which may occur through classical and quantum regimes, depending on the temperature range. Similar effects at ambient pressure may be obtained from chemical substitution. Compression of benzene illustrates irreversible transformations, obtained from multiple bond systems, leading to a dense amorphous material.

Polarization processes in electrorheological fluids based on conductive polymers

AbstractElectrorheological (ER) fluids are composed of dielectric particles dispersed in an inert liquid of low electric permittivity. Upon the application of an electric field ER fluids rapidly solidify, or increase their viscosity. Characteristic increase of the viscosity of ER fluids is due to the formation of particle chains that bridge the electrodes. This process is greatly affected by polarization processes within the solid phase and at the surface of the grains. These phenomena are governed by dopants, functional groups, structure of the solid particles and the solid/liquid interface. To find relations between parameters of the ER effect and material properties of components of ER fluids, two main types of the materials were investigated: conjugated polymers [polyphenylene (PPP), pyrolyzed polyacrylonitrile (PAN) and polythiophene] and solid electrolytes based on polyacrylonitrile complexed with inorganic salts. It was found that the ER activity resulted from surface polarization processes due to the presence of polar species (PAN) or bulk polarization related to mobile ions (PPP). Polythiophene, despite the presence of a conjugated system of multiple bonds, showed only residual ER effect. Solid electrolyte‐based fluids exhibited relatively high activity originated from ionic polarization. Copyright © 2006 John Wiley & Sons, Ltd.

CONJUGATED POLYMERS AS ACTIVE COMPONENTS OF ELECTRORHEOLOGICAL FLUIDS

ER properties of suspensions of four conjugated polymers - polyaniline, polyphenylene, polythiophene and pyrolysed polyacrylonitrile - in relation to their electric properties and chemical nature were studied. The polymer samples were synthesized and characterized by various methods and flow curves of their mixtures with silicone oil were recorded under electric field. It was found that the ER activity resulted from surface polarization processes due to presence of polar species (polyaniline and pyrolysed polyacrylonitrile) or bulk polarization related to mobile ions (polyphenylene). Polythiophene, despite its conjugation, showed only residual ER effect. The main conclusion is that many conducting (conjugated) polymers exhibit ER activity but the most characteristic and important feature of these materials – the conjugated system of multiple bonds – does not seem to be responsible for that. The electronic conductivity resulting from the conjugation contributes to higher currents which is unfavourable for technical applications. Conjugated polymers are ER active due to the enhanced mobility of ions within the bulk of particles dispersed in a liquid matrix and/or polar groups present on their surface.

Modification of the Wiener Index. 2.

A novel topological index based on the Wiener Index is proposed as W = 1/2, summation(n/ij)=S*(ij) the element S*(ij) of the distance matrix is defined either as S*(ij)= square root (E(i)E(j)/R(ij) (atoms i and j are adjacent) or as S*(ij)=(j-i+1)square root (E(i)...xE /R(ij) (atoms i and j are not adjacent), where E(i) and E(j) represent the total energy of the valence electrons of vertexes i and j, respectively, R(ij) is the sum of the distance between the vertexes i and j in a molecular graph. The distance and the energy of the vertexes in a molecule are taken into account in this definition. Hence the application of the index W to multiple bond and heteroatom-containing organic systems and inorganic systems is possible. Good correlation coefficients are achieved not only in the standard formation enthalpy of methyl halides, halogen-silicon, but also in the retention index of gas chromatography of the hydrocarbons.

Copper‐Mediated Addition and Substitution Reactions of Extended Multiple Bond Systems

AbstractFor Abstract see ChemInform Abstract in Full Text.

Hydrophosphination with cationic primary phosphine iron complexes: synthesis of P-chiral functionalized phosphines

The synthesis of P-chiral secondary phosphines, characterized by phosphorus and side chain chirality, has been realized via insertion of various organic multiple bond systems into the PH-bond of the primary phosphine complexes {C 5R 5(OC) 2Fe[P(R′)H 2]}BF 4 (R=H, Me; R′=alkyl, aryl). In the case of acetylenedicarboxylic acid dimethylester a double hydrophosphination is observed, leading diastereospecifically to the dinuclear complexes {C 5R 5(OC) 2Fe{P(H)(R′)[C(H)(CO 2Me)]}} 2(BF 4) 2 (R=H, Me; R′= t-Bu, 2-py), bearing four stereogenic centers. The use of p-benzoquinone gives access to secondary 2,5-bis(hydroxy)aryl phosphine ligands, suitable for further derivatizations. α-Hydroxyalkyl phosphine iron complexes can be obtained by hydrophosphination of aldehydes and ketones. Transformation into highly functionalized tertiary phosphine complexes is performed by a further hydrophosphination step using the alkenes H 2CCHX (X=CN, 2-py), diazoacetic ethylester, p-benzoquinone or ethylisocyanate, respectively, in special cases formation of functionalized azaphospholane ligands is observed. Release of the phosphines from the metal is achieved by photoinduced ligand exchange. In addition, primary phosphine iron complexes {C 5H 5(diphos)Fe[P(R)H 2]}BF 4 (diphos=DIOP, CHIRAPHOS) bearing chiral bis(phosphine) ligands have been used to provide the stereocontrol of the hydrophosphination process.

Synthesis of Phosporus Heterocycles using the Donor-Stabilized Dithiomonometaphosphoryl Chloride as Preparative Tool

The reactivity of the donor-stabilized monometaphosphoryl chloride Py⇒PS2Cl (1) versus multiple bond systems and organometallic compounds has been studied. Thus, on the reaction of 1 with diphenyl acetylene at elevated temperature the five-membered ring systems 2–4 are formed. In the first step probably cycloaddition of the intermediary liberated free monometaphosphoryl chloride PS2Cl with diphenyl acetylene leads to the 1-thia-phosphacyclobut-3-ene 6. This assumption will be supported by theoretical calculations. Attempts to eliminate one sulfur atom from the disulfide bridge in 2 result in the bicyclic ring system 5 besides a compound which is assumed to be 6. The reaction of 1 with tertBuLi gives the dithiaphosphetane 7 whereas with NaN(SiMe3)2 the diazadiphosphetidine 8 is obtained.

Protonation of 5,10,15,20-tetraphenylsapphyrin—identification of inverted and planar dicationic forms

5,10,15,20-Tetraphenylsapphyrin (TPSH3, I0) presents an unusual structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrolic unit. The acid–base chemistry of sapphyrin, involving hydrogen chloride, dichloroacetic acid or trifluoroacetic acid in chloroform, dichloromethane (293 and 203 K) and DMSO (293 K) has been followed by means of UV–VIS electronic and 1H NMR spectroscopy. The protonation of TPSH3 proceeds stepwise via a mono- and a variety of di-cationic forms. The monoprotonated species (I1) preserves the inverted skeleton of I0. Two fundamental structures, inverted (I2) and expanded (P2), have been detected in the case of dications. The transformation of the macrocycle involves a reversible flip of a single pyrrole unit which relocates the 27-NH pyrrolic nitrogen between the periphery and the centre of macrocycle (I⇌P). The rearrangement is triggered by proton and/or anion addition and involves binding of anion(s) via a system of multiple NH-anion hydrogen bonds. The sequence of structural transformation is solvent dependent: I0→I1→P2→I2 in dichloromethane (chloroform) but I0→I1→I2→P2 in DMSO for all investigated acids.

High-levelab initio versus DFT calculations on (H2O2)2 and H2O2-H2O complexes as prototypes of multiple hydrogen bond systems

The performance of B-LYP, B-P86, B3-LYP, B3-P86, and B3-PW91 density functionals to describe multiple hydrogen bond systems was studied. For this purpose we have chosen the dimers of hydrogen peroxide and the hydrogen peroxide–water complexes. The geometries and vibrational frequencies obtained with a 6-311+G(d,p) basis set were compared with those obtained at the MP2 level using the same basis set expansion. The corresponding dimerization energies were obtained using a 6-311+G(3df,2p) basis set and compared with those obtained using the G2(MP2) theory. Red shiftings of the OH donor stretching frequencies were predicted by all approaches investigated; however, in all cases, the DFT values were sizably larger than the MP2 ones. Similarly, the blue shifting of the torsion of the hydrogen peroxide subunit was larger when evaluated at the DFT level. All functionals reproduced the G2(MP2) relative stabilities of the different local minima quite well. With the exception of the B-LYP and B3-PW91 approaches, all functionals yielded binding energies which deviated from the G2(MP2) values by less than 0.5 kcal/mol, provided that G2-type basis sets were used and that the corresponding BSSE corrections were included. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1124–1135