Showing papers on "Substituent published in 2009"

A Meta-Selective Copper-Catalyzed C–H Bond Arylation

Abstract: For over a century, chemical transformations of benzene derivatives have been guided by the high selectivity for electrophilic attack at the ortho/para positions in electron-rich substrates and at the meta position in electron-deficient molecules. We have developed a copper-catalyzed arylation reaction that, in contrast, selectively substitutes phenyl electrophiles at the aromatic carbon-hydrogen sites meta to an amido substituent. This previously elusive class of transformation is applicable to a broad range of aromatic compounds.

Polymeric Modification of Graphene through Esterification of Graphite Oxide and Poly(vinyl alcohol)

Abstract: Soluble graphene covalently functionalized with poly(vinyl alcohol) (PVA) has been synthesized by simple esterification reaction of carboxylic groups in graphite oxide using two different synthetic strategies. Graphene has emerged to be a promising material due to its novel electrical transport properties. However, the use of graphene is limited by the lack of an effective method for large-scale production. Several chemical methods have been explored to obtain soluble graphene including the reduction of graphite oxide (GO) in a stabilization medium and covalent modification by amidation of the carboxylic groups, nucleophilic substitution to epoxy groups, and the diazonuim salts coupling. These modified graphenes provide opportunities for researchers to employ them in designing new materials, such as polymer nanocomposites. In such materials, controlling the interfacial interaction between the filler and the polymer is crucial to control the properties. Although graphene-based polymeric nanocomposites have been developed, polymer chains have not been used to covalently modify graphene. Nevertheless, polymer-bounded carbon nanotubes (CNT) and fullerene (C60) 8 have been widely studied. PVA-functionalized CNTs have been obtained by esterification reaction and used as fillers in nanocomposites. In that sense, the presence of COOH in the edge planes of GO can be exploited to anchorage PVA by using a similar way. In this Communication, we report the covalent functionalization of graphene sheets with PVA (Scheme 1). We employed two synthetic strategies. The first one involves the direct esterification of GO, while the second one goes through its acyl chloride derivative (GOCl) (Supporting Information). The obtained products, named as GO-es-PVA and GOCl-es-PVA, are soluble in DMSO and water with the aid of heat, similar to PVA and PVACNT. In the present research a special interest has been paid to the isolation and characterization of the PVA-functionalizedGO. First, an appropriate elimination of the no reacted GO was achieved by centrifugation, which completely removes the GO and leaves the PVA-functionalized GO (see Supporting Information). A comprehensive spectroscopic analysis was carried out to ensure that the esterification reactions were successfully completed. The HNMR spectrum of the soluble GO-es-PVA andGOCles-PVA in DMSO-d6 are compared with that of neat PVA (Figure S2). The latter exhibits the polymer backbone signals at ∼3.82 ppm (methine) and ∼1.38 ppm (methylene) and the hydroxyl signals at 5-4 ppm, from which the stereoregularity of PVA is estimated as isotactic (mm):hetero (mr): syndiotactic (rr) of roughly 2:5:3. Upon the attachment to GO the PVA proton signals become a littlewider butmaintain similar chemical shifts (Figure S2). The signals are less broadened than in PVACNT suggesting that, in principle, a lower degree of functionalization was achieved in our case. It is interesting to pay special attention to the hydroxyl protons resonances which are resolvable in terms of configurational sequences (Figure 1). Several authors have concluded that the hydrogen-bonding tendency, which is dominant for hydroxyl units in a meso configuration, predominantly determines the hydroxyl proton shielding. Since hydrogen bonding leads to downfield shifts, the chemical shifts of hydroxyl sequences resonances increase when passing from iso (4.7 ppm) to hetero (4.5 ppm) and fromhetero to syndio (4.2 ppm) triad.On the other hand, it has been demonstrated that the reactivity of substituent groups along the polymer chain can be influenced by tactic sequence where the substituent atmm sequence exhibited higher reactivity than those at the rr counterpart. By a mere inspection of the evolution of the H spectrum, we can easily observe an increase in the rr signal in detriment of the mm one for both GO-es-PVA and GOCl-es-PVA which suggests that esterification reaction occur at isotactic configuration. Surprisingly, as shown in Figure 1, a new signal at 4.2 ppm upfield, very closed to the rr triads of unmodified PVA, is clearly observed in spite of the low degree of esterification. This signal can be related to hydroxyl protons next to acetate groups as have been reported for esterification of PVA. By integration of this H NMR signal we can evaluate, within the experimental uncertainties, the degree of functionalization, obtaining a modification of around 1.8%. Interestingly, this value is reasonably low due to the huge volume of graphitic laminates (GLs) and is in agreement with the decrease ofmm triad content, as consequence of being less sterically hindered internally than those at syndiotactic counterpart, specifically in the incorporation of the GLs. The FTIR spectra of GO-es-PVA and GOCl-es-PVA retained most of the bands of PVA, although some of them changed in intensity or even disappeared due to the modification, and show new bands (Figure 1). The development of the band at 1715 cm suggests the presence of new carbonyl species. This band is most often related to the CdO stretching motions of COOHgroups situated at the edges of theGO lamellae and has low intensity due to high aspect ratio of GO which makes the relative amount of edge sites very small. Similarly, in our case the band at 1715 cm can be attributed to CdO stretching of ester groups. Indeed, this band was also observed in the esterification reaction of PVA and glycerol, suggesting that esterification is also taking place in our system. This is confirmed by the marked increase in the band around 1640 cm, which appears weakly in PVA and has been assigned to adsorbedwater. However, this is a strong band centered at 1628 cm in the spectrum of the GO (Figure S1), and although may also be due to adsorbed water, it contains a significant contribution from the skeletal vibration of nonoxidized graphitic domains. In addition, some interesting changes in the relative intensities of the characteristics bands of PVA in the 1200-1000 cm region can be observed. These bands are attributed to the C-O of doubly H-bonded OH in crystalline regions (1144 cm) and C-O unbonded in amorphous zones (1096 cm). The intensity ratio of these bands (I1144/I1096) diminishes markedly for the esterified products, suggesting a large decrease in the degree of crystallinity of the modified polymer. Raman data further confirm the presence of GLs covalently bonded to PVA chains (Figure S3). The Raman spectra for *Corresponding author: Fax þ34 915 644 853; Tel þ34 915 622 900; e-mail horacio@ictp.csic.es. D ow nl oa de d by C SI C M L O R A T A M A Y O Q U IM O R G o n Se pt em be r 1, 2 00 9 | h ttp :// pu bs .a cs .o rg

A series of halogenated heterodimeric inhibitors of prostate specific membrane antigen (PSMA) as radiolabeled probes for targeting prostate cancer.

Abstract: Prostate specific membrane antigen (PSMA) is a validated molecular marker for prostate cancer. A series of glutamate-urea (Glu-urea-X) heterodimeric inhibitors of PSMA were designed and synthesized where X = epsilon-N-(o-I, m-I, p-I, p-Br, o-Cl, m-Cl, p-Cl, p-F, H)-benzyl-Lys and epsilon-(p-I, p-Br, p-Cl, p-F, H)-phenylureido-Lys. The affinities for PSMA were determined by screening in a competitive binding assay. PSMA binding of the benzyllysine series was significantly affected by the nature of the halogen substituent (IC(50) values, Cl < I = Br << F = H) and the ring position of the halogen atom (IC(50) values, p-I < o-I << m-I). The halogen atom had little affect on the binding affinity in the para substituted phenylureido-Lys series. Two lead iodine compounds were radiolabeled with (123)I and (131)I and demonstrated specific PSMA binding on human prostate cancer cells, warranting evaluation as radioligands for the detection, staging, and monitoring of prostate cancer.

Guide to fluorine NMR for organic chemists

Abstract: PREFACE. 1 GENERAL INTRODUCTION. 1.1. Why Fluorinated Compounds are Interesting. 1.2. Introduction to Fluorine NMR. References. 2 AN OVERVIEW OF FLUORINE NMR. 2.1. Introduction. 2.2. Fluorine Chemical Shifts. 2.3. Spin-Spin Coupling Constants to Fluorine. 2.4. 1 H Spectra of Fluoroorganic Compounds. 2.5. 13 C NMR Spectra of Fluoroorganic Compounds. 2.6. Isotope Effects on Chemical Shifts. 2.7. Advanced Topics. References. 3 THE SINGLE FLUORINE SUBSTITUENT. 3.1. Introduction. 3.2. Saturated Hydrocarbons. 3.3. Influence of Substituents/Functional Groups. 3.4. Carbonyl Functional Groups. 3.5. Nitriles. 3.6. Alkenes with a Single Fluorine Substituent. 3.7. Acetylenic Fluorine. 3.8. Allylic, Propargylic, and Benzylic Fluorides. 3.9. Fluoroaromatics. 3.10. Fluoroheterocycles. 3.11. Other Common Groups with a Single Fluorine Substituent. References. 4 THE CF 2 GROUP. 4.1. Introduction. 4.2. Saturated Hydrocarbons Containing a CF 2 Group. 4.3. Influence of Substituents/Functional Groups. 4.4. Carbonyl Functional Groups. 4.5. Nitriles. 4.6. Bifunctional CF 2 Compounds. 4.7. Alkenes and Alkynes. 4.8. Benzenoid Aromatics Bearing a CF 2 Group. 4.9. Heteroaromatic CF 2 Groups. References. 5 THE TRIFLUOROMETHYL GROUP. 5.1. Introduction. 5.2. Saturated Hydrocarbons Bearing a CF 3 Group. 5.3. Influence of Substituents and Functional Groups. 5.4. Carbonyl Compounds. 5.5. Nitriles. 5.6. Bifunctional Compounds. 5.7. Sulfonic Acid Derivatives. 5.8. Allylic and Propargylic Trifluoromethyl Groups. 5.9. Aryl-Bound Trifluoromethyl Groups. 5.10. Heteroaryl-Bound Trifluoromethyl Groups. References. 6 MORE HIGHLY FLUORINATED GROUPS. 6.1. Introduction. 6.2. The 1,1,2- and 1,2,2-Trifluoroethyl Groups. 6.3. The 1,1,2,2-Tetrafluoroethyl and 2,2,3,3-Tetrafluoropropyl Groups. 6.4. The 1,2,2,2-Tetrafluoroethyl Group. 6.5. The Pentafluoroethyl Group. 6.6. The 2,2,3,3,3-Pentafluoropropyl Group. 6.7. The 1,1,2,3,3,3-Hexafluoropropyl Group. 6.8. The Hexafluoro- iso -Propyl Group. 6.9. The Heptafluoro- n -Propyl Group. 6.10. The Heptafluoro- iso -Propyl Group. 6.11. The Nonafluoro- n -Butyl Group. 6.12. Fluorous Groups. 6.13. 1-Hydro-Perfluoroalkanes. 6.14. Perfluoroalkanes. 6.15. Perfluoro- n -Alkyl Halides. 6.16. Perfluoroalkyl Amines, Ethers, and Carboxylic Acid Derivatives. 6.17. Polyfluoroalkenes. 6.18. Polyfluorinated Aromatics. 6.19. Polyfluoroheterocyclics. References. 7 COMPOUNDS AND SUBSTITUENTS WITH FLUORIDE DIRECTLY BOUND TO A HETEROATOM. 7.1. Introduction. 7.2. Boron Fluorides. 7.3. Fluorosilanes. 7.4. Nitrogen Fluorides. 7.5. Phosphorous Fluorides. 7.6. Oxygen Fluorides (Hypofluorites). 7.7. Sulfur Fluorides. 7.8. The Pentafluorosulfanyl (SF 5 ) Group. 7.9. Bromine Trifluoride and Iodine Pentafluoride. 7.10. Aryl Halogen Difluorides and Tetrafluorides. 7.11. Xenon Difluoride. References. GENERAL INDEX. COMPOUND INDEX.

Intermolecular olefin functionalisation involving aryl radicals generated from arenediazonium salts.

Abstract: This minireview is aimed at giving an overview of recent advances in olefin functionalisation reactions involving aryl radicals generated from arenediazonium salts. Based on the well-known Meerwein arylation, in which an aryl and a halogen substituent are coupled to an olefinic substrate, new reaction types have been developed that allow the introduction of a broad spectrum of other atoms and functional groups at the place of the original halogen atom and that are applicable to an extended range of olefinic substrates.

Pyrimidine compound and pests controlling composition containing the same

Abstract: The present invention relates to a pyrimidine compound of the formula (I):wherein R1 represents a hydrogen atom, halogen atom or C1-C4 alkyl; R2 represents C3-C7 alkynyloxy; R3 represents a hydrogen atom, halogen atom or C1-C3 alkyl; X represents C4-C7 polymethylene, in which a CH?2#191-CH?2#191 may be replaced with a CH=CH, optionally substituted with at least one substituent selected from the group consisting of halogen atoms, trifluoromethyl and C1-C4 alkyls. This pyrimidine compound has an excellent activity of controlling pests.

Precursors for depositing silicon-containing films and methods for making and using same

Abstract: Aminosilane precursors for depositing silicon-containing films, and methods for depositing silicon-containing films from these aminosilane precursors, are described herein. In one embodiment, there is provided an aminosilane precursor for depositing silicon-containing film comprising the following formula (I): (R 1 R 2 N) n SiR 3 4-n (I) wherein substituents R 1 and R 2 are each independently chosen from an alkyl group comprising from 1 to 20 carbon atoms and an aryl group comprising from 6 to 30 carbon atoms, at least one of substituents R 1 and R 2 comprises at least one electron withdrawing substituent chosen from F, Cl, Br, I, CN, NO 2 , PO(OR) 2 , OR, SO, SO 2 , SO 2 R and wherein R in the at least one electron withdrawing substituent is chosen from an alkyl group or an aryl group, R 3 is chosen from H, an alkyl group, or an aryl group, and n is a number ranging from 1 to 4.

Catalytic Asymmetric Intermolecular Stetter Reaction of Heterocyclic Aldehydes with Nitroalkenes: Backbone Fluorination Improves Selectivity

Abstract: The catalytic asymmetric intermolecular Stetter reaction of heterocyclic aldehydes and nitroalkenes has been developed. We have identified a strong stereoelectronic effect on catalyst structure when a fluorine substituent is placed in the backbone. X-ray structure analysis provides evidence that hyperconjugative effects are responsible for a change in conformation in the azolium precatalyst. This new N-heterocyclic carbene precursor bearing fluorine substitution in the backbone results in significantly improved enantioselectivities across a range of substrates.

Substituent Effects in Cation/π Interactions and Electrostatic Potentials above the Centers of Substituted Benzenes Are Due Primarily to Through-Space Effects of the Substituents

Abstract: Substituent effects in cation/π interactions have been examined using the M05-2X DFT functional and CCSD(T) paired with triple-ζ-quality basis sets. In contrast to popular, intuitive models, trends in substituent effects are explained primarily in terms of direct through-space interactions with the substituents. While there is some scatter in the data, which is attributed to π polarization, the trend in substituent effects in cation/π interactions is captured by an additive model in which the substituent is isolated from the aryl ring. Similarly, changes in the electrostatic potential at a point above the center of a substituted benzene arise largely from through-space effects of the substituents; π polarization is not the dominant underlying cause.

Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds. Substituent Effects in Phenethyl Phenyl Ethers

Abstract: Lignin is an abundant natural resource that is a potential source of valuable chemicals. Improved understanding of the pyrolysis of lignin occurs through the study of model compounds for which phenethyl phenyl ether (PhCH2CH2OPh, PPE) is the simplest example representing the dominant β-O-4 ether linkage. The initial step in the thermal decomposition of PPE is the homolytic cleavage of the oxygen−carbon bond. The rate of this key step will depend on the bond dissociation enthalpy, which in turn will depend on the nature and location of relevant substituents. We used modern density functional methods to calculate the oxygen−carbon bond dissociation enthalpies for PPE and several oxygen-substituted derivatives. Since carbon−carbon bond cleavage in PPE could be a competitive initial reaction under high-temperature pyrolysis conditions, we also calculated substituent effects on these bond dissociation enthalpies. We found that the oxygen−carbon bond dissociation enthalpy is substantially lowered by oxygen subs...

Carbon-carbon coupling of C(sp3)-F bonds using alumenium catalysis.

Abstract: Dialkylalumenium cation equivalents coupled with the hexabromocarborane anion function as efficient and long-lived catalysts for alkylation of aliphatic C-F bonds (alkylative defluorination or AlkDF) by alkylaluminum compounds. Only C(sp(3))-F bonds undergo AlkDF; C(sp(2))-F bonds are unaffected. Examples of compounds undergoing AlkDF include monofluoroalkanes, gem-difluorocyclopentane, and compounds containing a CF(3) group attached to either an aryl or an alkyl substituent. Conversion of C-F bonds to C-Me bonds is accomplished with high fidelity using Me(3)Al as the stoichiometric reagent. In reactions with Et(3)Al, hydrodefluorination of the C-F bonds is competitive with alkylation, indicative presumably of competitive hydride vs alkyl transfer from Et(3)Al. In a trialkylaluminum reagent, 1.1-1.4 alkyl groups per Al can be used to replace C-F bonds. Organoaluminum compounds efficiently remove water from the reaction mixture, obviating the need for rigorously dry solvents. Some organoaluminum compounds, especially methylaluminoxane, are capable of AlkDF with more reactive substrates, but catalysis by alumenium offers an advantage over the uncatalyzed C-F activation in terms of both increased rate and, in some cases, a dramatically increased selectivity.

Highly Enantioselective Benzoin Condensation Reactions Involving a Bifunctional Protic Pentafluorophenyl-Substituted Triazolium Precatalyst

Abstract: Improved catalyst design by incorporating a hydrogen bond donating substituent to improve enantiocontrol together with an acidifying pentafluorophenyl substituent to enhance catalyst efficiency results in a triazolium ion precatalyst that promotes the asymmetric archetypal benzoin condensation with excellent efficiency and unprecedented enantioselectivity.

Phosphorescence color tuning by ligand, and substituent effects of multifunctional iridium(III) cyclometalates with 9-arylcarbazole moieties.

Abstract: The synthesis, isomeric studies, and photophysical characterization of a series of multifunctional cyclometalated iridium(III) complexes containing a fluoro- or methyl-substituted 2-[3-(N-phenylcarbazolyl)]pyridine molecular framework are presented. All of the complexes are thermally stable solids and highly efficient electrophosphors. The optical, electrochemical, photo-, and electrophosphorescence traits of these iridium phosphors have been studied in terms of the electronic nature and coordinating site of the aryl or pyridyl ring substituents. The correlation between the functional properties of these phosphors and the results of density functional theory calculations was made. Arising from the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such a moiety can increase the highest-occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent phosphor with 2-phenylpyridine ligands. Remarkably, the excited-state properties can be manipulated through ligand and substituent effects that allow the tuning of phosphorescence energies from bluish green to deep red. Electrophosphorescent organic light-emitting diodes (OLEDs) with outstanding device performance can be fabricated based on these materials, which show a maximum current efficiency of approximately 43.4 cd A(-1), corresponding to an external quantum efficiency of approximately 12.9 % ph/el (photons per electron) and a power efficiency of approximately 33.4 Lm W(-1) for the best device. The present work provides a new avenue for the rational design of multifunctional iridium-carbazolyl electrophosphors, by synthetically tailoring the carbazolyl pyridine ring that can reveal a superior device performance coupled with good color-tuning versatility, suitable for multicolor-display technology.

Iridium/Monodentate Phosphoramidite Catalyzed Asymmetric Hydrogenation of N-Aryl Imines

Abstract: Asymmetric hydrogenation of N-aryl acetophenone imines using iridium/PipPhos leads to very high enantioselectivities up to >99% depending on the presence of electron-donating substituents in the 2-, 3-, and 5-position of the aryl ring. If the substituent is 2-methoxy, the resultant secondary amines are easily oxidatively deprotected using trichloroisocyanuric acid to give the primary amines in good yield with full retention of enantioselectivity.

Di- and tri-zinc catalysts for the low-pressure copolymerization of CO2 and cyclohexene oxide.

Abstract: The syntheses and characterization of three new macrocyclic proligands, with variation of the para aryl ring substituent, are reported. Dizinc and trizinc acetate complexes are prepared using these ligands and are characterized using infrared and nuclear magnetic resonance spectroscopies, mass spectrometry, elemental analysis, and, for the three trizinc complexes, single-crystal X-ray diffraction. The X-ray crystallographic and spectroscopic data indicate bridging and terminal acetate coordination modes, both in the solid state and in solution, for the trizinc complexes. All of the complexes show good turnover numbers and frequencies, under 1 atm of pressure of carbon dioxide, for the copolymerization of CO(2) and cyclohexene oxide to produce poly(cyclohexene carbonate). The electronic nature of the ancillary ligands' substituents influences the catalytic activity of the complex, with the electron-donating substituent reducing the activity. The dizinc catalysts show markedly higher activities than the trizinc analogues, suggesting that the coordination environment within the macrocycle is crucial to controlling the catalytic activity.

Double Bond Isomerization/Enantioselective Aza-Petasis−Ferrier Rearrangement Sequence as an Efficient Entry to Anti- and Enantioenriched β-Amino Aldehydes

Abstract: Highly anti- and enantioselective synthesis of β-amino aldehydes having an aliphatic substituent at the β-position was accomplished by a combination of two catalytic reactions, that is, an initial Ni(II) complex-catalyzed isomerization of a double bond followed by a chiral phosphoric acid catalyzed aza-Petasis−Ferrier rearrangement, using hemiaminal allyl ethers as the initial substrate. The chiral phosphoric acid also functioned as an efficient resolving catalyst of racemic hemiaminal vinyl ethers.

Palladium-catalyzed insertion of alpha-diazoesters into vinyl halides to generate alpha,beta-unsaturated gamma-amino esters.

Abstract: As easy as 1, 2, 3: A palladium-catalyzed three-component coupling generates alpha,beta-unsaturated gamma-amino acids in a single step (see scheme). The reaction is believed to involve migration of a vinyl substituent to a highly electrophilic palladium carbene. Unlike previous synthetic approaches, this synthesis provides access to gamma-amino acids with non-natural side chains.

Substituent Effect on the Meso-Substituted Porphyrins: Theoretical Screening of Sensitizer Candidates for Dye-Sensitized Solar Cells

Abstract: According to the concepts of attribute axis and attribute coordinate system, porphine and 11 kinds of bridge carbon substituted porphyrins as donors and 9 common acceptors A-I have been designed and calculated at the density functional B3LYP level. The substituent effects on the molecular orbital energy levels of the porphyrin derivatives have been discussed and promising donor-acceptor combinations are screened. Several novel zinc metalloporphyrins selected were then calculated by means of the DFT/TDDFT method in THF solvent. The electronic and spectroscopic properties of ZnTPP and the selected novel zinc porphyrin complexes have been investigated as solar cell senstizers. The results show that the candidates selected are very promising to provide good performances as sensitizers, in which ZnTPPG is promising to challenge the current photoelectric conversion efficiency record 7.1% of porphyrin-sensitized solar cells. The concepts of attribute axis and attribute coordinate system are shown very helpful for tuning the molecular properties and the rational design of functional molecules with anticipated good properties.

Why do non-symmetric dimers intercalate? The synthesis and characterisation of the α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-(2-methylbutyl-4′-(4″-phenyl)benzoateoxy)alkanes

Abstract: Ten new non-symmetric liquid crystal dimers belonging to the family of compounds α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-(2-methylbutyl-4′-(4″-phenyl)benzoateoxy)-alkanes have been synthesised and their transitional properties characterised. The dimers contain either a hexamethylene or octamethylene spacer, while the terminal substituents on the 4-benzylideneaniline fragment are H, CH3, F, Cl and Br. The unsubstituted dimers are not liquid crystalline, while the remaining compounds exhibit enantiotropic nematic behaviour. The trends in the clearing temperatures, according to the chemical nature of the terminal substituent, are largely consistent with those established for conventional low molar mass liquid crystals. Three of the dimers also exhibit an intercalated smectic A phase, specifically the two bromo-substituted dimers and the chloro-substituted dimer containing a hexamethylene spacer. The driving force for the formation of this phase is considered to be, at least in part, the specific aniso...

The effect of electrostatic interactions on conformational equilibria of multiply substituted tetrahydropyran oxocarbenium ions.

Abstract: The three-dimensional structures of dioxocarbenium ions related to glycosyl cations were determined by an analysis of spectroscopic, computational, and reactivity data. Hypothetical low-energy structures of the dioxocarbenium ions were correlated with both experimentally determined (1)H NMR coupling constants and diastereoselectivity results from nucleophilic substitution reactions. This method confirmed the pseudoaxial preference of C-3 alkoxy-substituted systems and revealed the conformational preference of the C-5 alkoxymethyl group. Although the monosubstituted C-5 alkoxymethyl substituent preferred a pseudoequatorial orientation, the C-5-C-6 bond rotation was controlled by an electrostatic effect. The preferred diaxial conformer of the trans-4,5-disubstituted tetrahydropyranyl system underscored the importance of electrostatic effects in dictating conformational equilibria. In the 2-deoxymannose system, although steric effects influenced the orientation of the C-5 alkoxymethyl substituent, the all-axial conformer was favored because of electrostatic stabilization.

Platinum and Ruthenium Chloride-Catalyzed Cycloisomerization of 1-Alkyl-2-ethynylbenzenes: Interception of π-Activated Alkynes with a Benzylic C−H Bond

Abstract: Air-stable and commercially available alkynophilic metal salts, such as PtCl2, PtCl4, and [RuCl2(CO)3]2, catalyze the cycloisomerization of 1-alkyl-2-ethynylbenzenes to produce substituted indenes even at an ambient temperature. Electrophilically activated alkynes can be intercepted by simple benzylic C−H bonds at primary, secondary, and tertiary carbon centers. Mechanistic studies, such as labeling studies and kinetic isotope and substituent effects, indicate that the cycloisomerization proceeds through the formation of a vinylidene intermediate and turnover-limiting 1,5-shift of benzylic hydrogen.

Triphenylamine−Fluorene Alternating Conjugated Copolymers with Pendant Acceptor Groups: Synthesis, Structure−Property Relationship, and Photovoltaic Application

Abstract: Three triphenylamine−fluorene alternating conjugated copolymers, differing only in the aldehyde (PTCHO), monocyano (PTCN), and dicyano (PTDCN) pendant acceptor groups, have been designed and synthesized. The structures and properties of the conjugated copolymers were characterized by 1H NMR, elemental analysis, gel permeation chromatography (GPC), thermal gravimetric analysis (TGA), UV−visible absorption spectroscopy, photoluminescence (PL) spectroscopy, and cyclic voltammetry (CV). Through manipulating the acceptor attached to the same π-conjugated backbone, the electronic properties and energy levels of the copolymers were effectively tuned for blue, yellowish-green, and yellowish-orange emissions, resembling those of the primary colors. The effect of substituent on the electronic structure of the copolymers was also studied by molecular simulation. The blue shift in the π-π* transition of the backbone was associated with the variation in the structural geometry, whereas the charge transfer, excimer for...

Synthesis and Ligand Properties of a Persistent, All‐Carbon Four‐Membered‐Ring Allene

Abstract: A single donor substituent at each terminus is sufficient to make the CCC skeleton of allenes very flexible and give carbon(0) character to the central carbon atom. This allows the synthesis of a four-membered carbocyclic allene, which can be doubly protonated and behaves as a very strong eta(1)-donor ligand for transition metals (see scheme).

Hydrogen Elimination in Bulky Calcium Amidoborane Complexes: Isolation of a Calcium Borylamide Complex

Abstract: The decomposition route of N-substituted calcium amidoborane complexes depends on the steric bulk of the substituent. Relatively small substituents (R = H, Me, iPr) gave dehydrogenation to dimeric complexes with a bridging RN-BH-N(R)-BH(3)(2-) ion, whereas the larger 2,6-di-isopropylphenyl substituent resulted in formation of a complex with a borylamide anion: H(2)B(R)N(-). This product is a promising species for (catalytic) regeneration with H(2), i.e., hydrogenation to the amidoborane anion H(3)B(R)NH(-).