Site Selectivity in the Gas-Phase Ionic Phenylation of Alcohols and Alkyl Chlorides

Free, unsolvated phenylium ions formed by the spontaneous β decay of [1,4-³H₂]benzene have been allowed to react with gaseous alcohols (ROH: R = Et, CF₃CH₂, Pr, or i-Pr; partial pressure: 3–56 Torr) and alkyl chlorides (R′Cl: R′ = Pr, i-Pr, or Bu; partial pressure: 20–450 Torr), in the presence of a thermal radical scavenger (O₂: 4 Torr). Phenylium ion confirms its considerable site selectivity, demonstrated by the distinct preference toward the n-centre of the substrate (46–100%), although significant insertion into the alkyl group of alcohols is observed as well. Phenylium ion displays significant positional selectivity even between different n-type sites in a bidentate molecule such as CF₃CH₂OH. An affinity F < O < Cl trend is observed, which indicates a direct relationship between the polarizability of the n-centre of the molecule and its orienting properties toward phenylium ion. The stability features of the ionic intermediates from addition of phenylium ion with ROH or R′Cl have been evaluated, as well as their fragmentation and isomerization mechanisms. The behaviour of phenylium ion toward the selected substrates in the gas phase is discussed and compared with previous mechanistic hypotheses from related nuclear-decay studies.     

Reactions of phenylium ions with gaseous hydrocarbons. 1. methane,ethane, and propane

The reaction of free tritiated phenylium ion, generated from nuclear decay of [l,4-T₂]-benzene in the presence of simple gaseous hydrocarbons RH (R = CH₃, C₂H₅, C₃H₇; partial pressure: 10-100 torr), yields predominantly the corresponding tritiated C₆H₅R products. The effects of gaseous nucleophilic acceptors (NuH = NH₃, CH₃OH) on the reaction with CH₄, were also investigated. Phenylium ion confirms its exceedingly high reactivity even toward pure σ- -type substrates, as well as its considerable site selectivity, demonstrated by the distinct preference for the C-H bonds of the substrate. The stability features of the ionic intermediates from addition of phenylium ion with RH have been evaluated, as well as their fragmentation and isomerization mechanisms. The behaviour of phenylium ion toward simple aliphatic hydrocarbons in the gas phase (10-100 torr) is discussed and compared with previous mechanistic hypotheses from ICR mass spectrometric studies, carried out at much lower pressures (10^-5 torr).     

Gas-phase reactions of free phenylium cations with C3H6 hydrocarbons

Free, unsolvated phenylium ions formed by the spontaneous β decay of a constituent atom of multitritiated benzene have been allowed to react with gaseous propene and cyclopropane in the pressure range from 10 to 700 torr. Phenylium ions attack efficiently both the C-H and the C-C bonds of cyclopropane, yielding respectively tritiated cyclopropylbenzene and indane as the major products. Selective attack of phenylium ions on the π bond of propene is suggested by the composition of tritiated products, isomeric phenylpropenes and isopropylbenzene. The different behavior of propene and cyclopropane toward gaseous phenylium ions is consistent with the results of related radiolytic investigations concerning gaseous systems at nearly atmospheric pressure. The reactivity pattern of the isomeric C₃H₆ hydrocarbons toward gaseous phenylium ions is discussed and compared with pertinent mass spectrometric data.     

First evidence for automerization of gaseous phenylium ion.

Tritium atom distribution in the anisole formed from the attack of a nucleogenic tritiated phenylium ion on gaseous methanol provides the first experimental evidence for a gas-phase automerization of phenylium ion.     

Reactions of (η6-Arene)tricarbonylchromium Complexes: Hydrogenation,Nitration, and Bromination

In this study, we explore the reactions of coordinated arenes, e.g., hydrogenation, nitration, and bromination, to prepare compounds which are not accessible from conventional organic synthesis. The reaction products formed from reactions with the coordinated and the uncoordinated arenes are compared. The polycyclic aromatic hydrocarbons (PAHs) employed for this study include phenanthrene, methyl- and acetyl-phenanthrene, and benz[a]anthracene (BA), The tricarbonylchromium group demonstrated various characteristics which influence the reactions in this work, such as an electronic effect to deactivate hydrogenation, a steric effect to exhibit, highly positional selective nitration, and a free radical mechanism to direct bromine to attack at the ring coordinated to tricarbonylchromium.     

How difficult are anion-molecule SNAr reactions of unactivated arenes in the gas phase,dimethyl sulfoxide,and methanol solvents?

Nucleophilic substitution on the aromatic ring (S_NAr) is a very important reaction for organic transformations. This kind of reaction is usually difficult to take place, requiring organometallic catalysis or activation of the ring by electron withdrawing groups to turn the nucleophilic attack possible. In this work, the relative importance of intrinsic gas phase barrier and the solvent effect on several S_NAr reactions using theoretical calculations were investigated. The reactions of the anions OH^?, CN^?, and CH₃O^? and the enolates CH₃COCH₂^? and CH₃COCHCOCH₃^? with bromobenzene and (o, m, p)-methoxy bromobenzene in methanol and dimethyl sulfoxide as solvents were considered. The OH^? and CH₃O^? ions are highly reactive in the gas phase. However, the solvent effect induces a high activation barrier in solution, turning the reaction difficult, although feasible. The CN^? and CH₃COCHCOCH₃^? ions have high activation barriers even in the gas phase. The interesting CH₃COCH₂^? ion has a moderate barrier in the gas phase, although the free energy barrier in DMSO solution reaches 33 kcal mol^?1. Our analysis suggests that decreasing the solvent effect, arylation of enolates with unactivated arenes could become possible.

     

The mass spectra of styryl sulfoxides and sulfones

A variety of rearrangement reactions have been documented in the gas phase ion chemistry of styryl sulfoxides and sulfones. The styryl group rearranges from sulfur to oxygen as evidenced by loss of SCH₃ from methyl styryl sulfoxide and loss of SOCH₃ from the corresponding sulfone. The resulting m/e 119 ion loses carbon monoxide in one fragmentation route and alternatively loses a hydrogen atom from the aromatic nucleus to produce the benzofuran molecule ion via an electrophilic aromatic ring closure reaction. Styryl sulfoxides lose both carbon monoxide and formyl radicals directly from their molecule ions, but the corresponding sulfones do not fragment in this manner. The mechanisms of the above reactions, as well as others, were investigated using substituent and deuterium labeling. The styryl group has been shown to migrate in preference to a phenyl or substituted phenyl group by investigation of the mass spectra of appropriate aryl styryl sulfoxides and sulfones.     

Radical-induced aromatic substitution between benzoyl peroxide and benzenediols in the gas phase characterized by mass spectrometry

A radical-induced aromatic substitution mechanism for the reaction between benzoyl peroxide and benzenediols in the gas phase was characterized by mass spectrometry. The benzoyloxy radical produced from the homolysis of benzoyl peroxide associates at its carbonyl group with the phenolic hydroxyl group. The pairing tendency of the unpaired electron on the oxygen of the radical induces electron transfer along the hydrogen bond, which results in the rupture of the O? H bond of the phenol and aromatic substitution at the ortho position of the benzoyloxy radical. Supporting evidence for the mechanism was obtained by isotope labelling.     

Synthesis and binding studies of novel bisthiacalix[4]arenes with diimime linkages

A series of novel bisthiacalix[4]arenes with diimine linkages of different aromatic or heteroaromatic dialdehydes have been synthesized. The structure of one of the bisthiacalixarene has been analyzed by X-ray crystallography. These molecules quantitatively extract silver ion from aqueous into organic phase under neutral conditions.     

Free radical 4‐nitrophenylation of thieno[2,3‐b]pyridine. Part 1: General experimental procedure and prediction of isomeric ratios of products

Thieno[2,3‐b]pyridine (1) was warmed at 45 ± 7° with diazotized 4‐nitroaniline ( 2 ) (molar ratio 1:2 = 3.6:1) in buffered (sodium acetate‐acetic acid) aqueous solution until gas evolution ceased. The reaction mixture was separated into these fractions: (a) water‐soluble (discarded), (b) acetone‐soluble (tars), (c) ether‐soluble, and (d) ether‐ and chloroform‐soluble, but acetone‐insoluble (rust‐colored solids, Y , 12% yield as 4‐nitrophenyl‐ 1 isomers, 3 ). Fractional evaporative distillations of (b) and (c) gave recovered 1 (69%) and yellow‐red sublimates (Z, 20% yield as 3 ). Y and Z were handled separately for isolation and identification of isomers [2]. Three general methods for predicting the isomeric ratios of 3 which one should obtain are presented, viz. (1) an amalgamation of reported free‐radical phenylation results for quinoline and benzo[b]thiophene, (2) calculations of Frontier Radical Densities for positions 2‐6 only, and (3) Molecular Orbital calculations for electron densities and superdelocalizabilities for free‐radical attack at positions 1‐7, as modified by a proposed rearrangement of the attacking group from the heteroatomic N and S positions to adjacent alpha positions.     

Extractive Refining of the Kerosene Fraction with Recovery of Aromatic Petroleum Solvents

Jet fuel containing less than 10 wt % arenes and aromatic petroleum solvents of the Nefras AR-120/200 type was prepared by combination of arene extraction from the hydrorefined kerosene fraction with the acetonitrile-pentane system, followed by concentration of arenes in the course of acetonitrile regeneration from the extract phase, based on the formation of azeotropes of acetonitrile with saturated C₉-C₁₀ hydrocarbons.     

Catalyst‐Free Polyhydroboration of Dodecaborate Yields Highly Photoluminescent Ionic Polyarylated Clusters

The incorporation of polyhedral boranes into novel photoluminescent materials is an area with increasing interest. While the neutral carboranes have been widely investigated for this purpose, the dodecaborate ion has received much less attention. Herein we report a significant expansion to the scope of substitution reactions for the dodecaborate ion, whereby this cluster was observed to react directly with a wide range of arenes in a step‐wise and controlled manner. In the products of these reactions, the dodecaborate ion serves as a core upon which up to nine mono‐ or polycyclic aromatic hydrocarbon ligands are exohedrally bonded. Spectroscopic evidence suggests the presence of conjugation between the π systems of the aryl ligands and the dodecaborate core, resulting in materials which exhibit high solution‐phase photoluminescence, as well as molar absorptivities and Stokes shifts that are significantly larger than those of the free arenes from which they were derived. We propose that this broad reactivity is a valuable synthetic tool for the incorporation of polyhedral boron into novel organic structures.     

Open‐tubular capillary electrochromatography using carboxylatopillar[5]arene as stationary phase

Pillar[n]arenes have achieved much interest in material chemistry and supramolecular chemistry due to unusual pillar shape structure and high selectivity toward guest. However, pillar[n]arenes have not yet been applied in capillary electrochromatography. This work at first time reports that carboxylatopillar[5]arene is used as a stationary phase in open‐tubular capillary electrochromatography. Carboxylatopillar[5]arene not only possess the advantages of pillar[n]arenes but also provide free carboxy groups for immobilizing on the inner wall of capillary column via covalent bonding. The characterization of SEM and FT‐IR indicated that carboxylatopillar[5]arene was successfully grafted on the inner wall of capillary. The baseline separation of model analytes including neutral, basic, and acidic compounds, nonsteroidal anti‐inflammatory drugs and dansyl‐amino acids have been achieved thanks to the electron‐rich cavity of carboxylatopillar[5]arene and hydrophobic interactions between the analytes and stationary phase. The intraday, interday, and column‐to‐column precisions (RSDs) of retention time and peak area for the neutral analytes were all less than 3.34 and 9.65%, respectively. This work indicates that pillar[n]arenes have great potential in capillary electrochromatography as novel stationary phase.     

Origin of the Regioselectivity in the Gas‐Phase Aniline+CH3+ Electrophilic Aromatic Substitution

Nonadiabatic ab initio molecular dynamics simulations are carried out to monitor the attack of CH₃⁺ on aniline in the gas phase to form the corresponding σ complexes. The reaction is ultrafast and is governed by a single electron transfer within 30 fs, which involves two sequential conical intersections and finally produces a radical pair. Positive‐charge allocation in the aromatic compound is found to govern the substitution pattern in ortho, meta, or para position. Although the major products in the first step of the electrophilic aromatic substitution are the ortho and para σ complexes, initially 26 % of the simulated trajectories also form meta complexes, which then undergo H shifts, mainly to the para position.     

Towards Ideal Synthesis: Alkenylation of Aryl CH Bonds by a Fujiwara–Moritani Reaction

An overview of recent progress in the Fujiwara–Moritani reaction, which is the palladium‐catalyzed oxidative coupling of arenes with olefins to afford alkenyl arenes, is described. It is emphasized that regioselectivity on aryl ortho‐ or meta‐C?H activation could be controlled very well in the presence of Pd, Rh, or Ru catalysts with the assistance of various chelation groups on aromatic rings in this coupling reaction. Catalytic alkenylation of aryl C?H bonds from simple arenes is also discussed, especially from electron‐deficient arenes. These advanced protocols would not only make the Fujiwara–Moritani reaction more useful and applicable in organic synthesis but also light the way for the further development of the functionalization of normal C?H bonds.     

Remote Enantioselective Friedel–Crafts Alkylations of Furans through HOMO Activation

Catalytic asymmetric Friedel–Crafts alkylation is a powerful protocol for constructing a chiral C(sp²)? C(sp³) bond. Most previous examples rely on LUMO activation of the electrophiles using chiral catalysts with subsequent attack by electron‐rich arenes. Presented herein is an alternative strategy in which the HOMO of the aromatic π system of 2‐furfuryl ketones is raised through the formation of a formal trienamine species using a chiral primary amine. Exclusive regioselective alkylation at the 5‐position occurred with alkylidenemalononitriles, and high reactivity and excellent enantioselectivity (up to 95 % ee) was obtained by this remote activation.     

Combined molecular mechanical and quantum mechanical potential study of a nucleophilic addition reaction in solution

The procedure of combined semiempirical quantum mechanical (AM1) and molecular mechanical potential⁷ was used to study the nucleophilic addition of hydroxide to formaldehyde in solution. The gas phase AM1 potential surface is approximately 26 kcal/mol more exothermic than the corresponding ab initio 6-31 + G* calculation results. The free energy profile for the reaction in solution was determined by means of molecular dynamic simulations. The resulting free energy of activation is approximately 5 kcal/mol. The difference of the free energy of solvation between the reactant and the product states is about 38 kcal/mol. As the reaction goes on, the number of hydrogen bonds formed by the hydroxide oxygen with the surrounding water molecules decreases, whereas the number of hydrogen bonds formed by the carbonyl oxygen increases. There is no significant change in the total number of hydrogen bonds between the solute and the solvent molecules, and the average number of these hydrogen bonds is between five and six during the entire reaction process. These results are consistent with previous studies using a model based on ad initio 6-31 + G* calculations in the gas phase. The reaction path in solution is different from the gas phase minimum energy reaction path. When the two reactants are at a large distance, the attack route of the hydroxide anion in solution is close to perpendicular to the formaldehyde plane, whereas in the gas phase the route is collinear with the carbonyl group. These results suggests that although AM1 does not yield accurate energies in the gas phase, valuable insights into the solvent effects can be obtained through computer simulations with this combined potential. This combined procedure could be applied to chemical reactions within macromolecules, in which a quantitative estimation of the effects of the environment would not be easily attainable by another technique. © 1994 by John Wiley & Sons, Inc.     

Noncovalent complex formation of tetratosylated resorcarene with aromatic,aliphatic, and cyclic alkyl ammonium ions: a mass spectrometric study of complex properties

The ability of tetratosylated resorcarene to form complexes with aromatic ammonium ions was investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The formation of noncovalent complexes, [1+guest]⁺ and [1 · 1+guest]⁺, as observed with singly charged aromatic anilinium and phenylene aminoammonium guests. Comparison of the complexation efficiencies of the aromatic and aliphatic ammonium ions showed the importance of proton affinity of conjugate amines in complex formation. In collision‐induced dissociation experiments, gas‐phase stability was found to be lower for complexes formed with aromatic ions and this behavior was not found to depend on the proton affinity of conjugate amines. Fast oxidation of the para and ortho aminoammonium ions and complexation of these ions with tetratosylated resorcarene was observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Identification of position isomers by energy‐resolved mass spectrometry

This study reports an energy‐resolved mass spectrometric (ERMS) strategy for the characterization of position isomers derived from the reaction of hydroxyl radicals (^●OH) with diphenhydramine (DPH) that are usually hard to differentiate by other methods. The isomer analogues formed by ^●OH attack on the side chain of DPH are identified with the help of a specific fragment ion peak (m/z 88) in the collision‐induced dissociation (CID) spectrum of the protonated molecule. In the negative ion mode, the breakdown curves of the deprotonated molecules show an order of stability (supported by density functional theory (DFT) calculations) ortho > meta > para of the positional isomers formed by the hydroxylation of the aromatic ring. The gas phase stability of the deprotonated molecules [M ? H]^? towards the benzylic cleavage depends mainly on the formation of intramolecular hydrogen bonds and of the mesomeric effect of the phenol hydroxyl. The [M ? H]^? molecules of ortho and meta isomers result a peak at m/z 183 with notably different intensities because of the presence/absence of an intramolecular hydrogen bonding between the OH group and C9 protons. The ERMS approach discussed in this report might be an effective replacement for the conventional methods that requires very costly and time‐consuming separation/purification methods along with the use of multi‐spectroscopic methods. Copyright © 2015 John Wiley & Sons, Ltd.     

The reaction of direct phenylation by nucleogenic cations as a method of synthesis of unknown or complicated tritium labeled compounds

As a result of ion-molecular reactions of nucleogenic phenyl cations, generated by tritium β-decay in polytritiated benzene, with nucleophilic centers of investigated substrates the direct phenylation has been realized at first time and unknown tritium labeled aromatic derivatives of polyvalent fluorine together with the different N-phenyl substituted pyridinium compounds which are important syntones for biological and medical investigations have been synthesized.