Amphiphilic homopolymer as a reaction medium in water: product selectivity within polymeric nanopockets

A styrene-based water-soluble polymer has been explored for its use as a host for lipophilic substrates in aqueous medium. Unimolecular reactions, namely, photo-Fries rearrangement of naphthyl esters, alpha-cleavage reaction of 1-phenyl-3-p-tolyl-propan-2-one, and Norrish type I and type II reactions of benzoin alkyl ethers were examined. We find that the hydrophobic domains generated by the polymer not only restrict the mobility of the radicals but also modestly incarcerate the substrate, intermediates, and products during the time scale of the reactions. Comparative studies of the same photoreactions in micelles formed from small molecule surfactants and an amphiphilic diblock copolymer demonstrate that the styrene-based water-soluble polymer aggregates in aqueous medium offer better selectivity.     

Silica Gel Catalyzed Conversion of Dialkyl 2-(1-Hydroxy-2-naphthyl)-3-(triphenylphosphoranylidene)butanedioates to Alkyl 2-Oxo-2 H -benzo[ h ]chromene-4-carboxylates in Solvent-Free Conditions

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 1-hydroxynaphthalene leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce dialkyl 2-(1-hydroxy-2-naphthyl)-3-(triphenylphosphanylidene)butanedioates. Silica gel was found to catalyze conversion of dialkyl 2-(1-hydroxy-2-naphthyl)-3-(triphenylphosphanylidene)butanedioates to alkyl 2-oxo-2 H -benzo[ h ]chromene-4-carboxylates in solvent-free conditions at 80°;C in fairly good yields.     

Silica Gel Catalyzed Conversion of Dialkyl 2-(2-Hydroxy-1-naphthyl)-3-(1,1,1-triphenyl-λ 5 -phosphanylidene) Succinates to Alkyl 3-Oxo-3 H -benzo[ f ]chromene-1-carboxylates in Solvent-free Conditions

Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by 2-hydroxynaphthalene leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce dialkyl 2-(1-hydroxy-2-naphthyl)-3-(1,1,1-triphenyl- u 5 -phosphanylidene) succinates. Silica gel was found to catalyze conversion of dialkyl 2-(1-hydroxy-2-naphthyl)-3-(1,1,1-triphenyl- u 5 -phosphanylidene) succinates to alkyl 3-oxo-3H-benzo[f]chromene-1-carboxylates in solvent-free conditions at 60°;C in fairly good yields.     

Selective formation of triplet alkyl nitrenes from photolysis of beta-azido-propiophenone and their reactivity

Photolysis of beta-azido propiophenone derivatives, 1, with built-in sensitizer units, leads to selective formation of triplet alkyl nitrenes 2 that were detected directly with laser flash photolysis (lambdamax = 325 nm, tau = 27 ms) and ESR spectroscopy (|D/hc| = 1.64 cm-1, |E/hc| = 0.004 cm-1). Nitrenes 2 were further characterized with argon matrix isolation, isotope labeling, and molecular modeling. The triplet alkyl nitrenes are persistent intermediates that do not abstract H-atoms from the solvent but do decay by dimerizing with another triplet nitrene to form azo products, rather than reacting with an azide precursor. The azo dimer tautomerizes and rearranges to form heterocyclic compound 3. Nitrene 2a, with an n,pi* configuration as the lowest triplet excited state of the its ketone sensitizer moiety, undergoes intramolecular 1,4-H-atom abstraction to form biradical 6, which was identified by argon matrix isolation, isotope labeling, and molecular modeling. beta-Azido-p-methoxy-propiophenone, with a pi,pi* lowest excited state of its triplet sensitizer moiety, does not undergo any secondary photoreactions but selectively yields only triplet alkyl nitrene intermediates that dimerize to form 3b.     

Solid-state cpmas 13C-NMR studies of the reaction of an epoxy resin with masked isocyanates

It has been shown that incorporation of masked isocyanates in the MY720/DDS epoxy significantly reduces the equilibrium moisture absorption by blocking of residual functional groups ( oxirane group) by the isocyanates released in the deblocking reaction of the masked isocyanates. We have now used high resolution ¹³C-CP/MAS NMR to follow the reactions in the solid state and to identify intermediates and by-products. The deblocking reaction of the masked isocyanates also releases the corresponding alcohol, part of which may evaporate during the curing reaction. The resolution in the solid-state spectra is good enough to identify all the reactants and the intermediates involved in the curing reaction. Difference spectra are used to emphasize changes between systems that differ in treatment or composition.     

Reaction mechanism of naphthyl radicals with molecular oxygen. 1. Theoretical study of the potential energy surface

Potential energy surfaces (PESs) of the reactions of 1- and 2-naphthyl radicals with molecular oxygen have been investigated at the G3(MP2,CC)//B3LYP/6-311G** level of theory. Both reactions are shown to be initiated by barrierless addition of O(2) to the respective radical sites of C(10)H(7). The end-on O(2) addition leading to 1- and 2-naphthylperoxy radicals exothermic by 45-46 kcal/mol is found to be more preferable thermodynamically than the side-on addition. At the subsequent reaction step, the chemically activated 1- and 2-C(10)H(7)OO adducts can eliminate an oxygen atom leading to the formation of 1- and 2-naphthoxy radical products, respectively, which in turn can undergo unimolecular decomposition producing indenyl radical + CO via the barriers of 57.8 and 48.3 kcal/mol and with total reaction endothermicities of 14.5 and 10.2 kcal/mol, respectively. Alternatively, the initial reaction adducts can feature an oxygen atom insertion into the attacked C(6) ring leading to bicyclic intermediates a10 and a10' (from 1-naphthyl + O(2)) or b10 and b10' (from 2-naphthyl + O(2)) composed from two fused six-member C(6) and seven-member C(6)O rings. Next, a10 and a10' are predicted to decompose to C(9)H(7) (indenyl) + CO(2), 1,2-C(10)H(6)O(2) (1,2-naphthoquinone) + H, and 1-C(9)H(7)O (1-benzopyranyl) + CO, whereas b10 and b10' would dissociate to C(9)H(7) (indenyl) + CO(2), 2-C(9)H(7)O (2-benzopyranyl) + CO, and 1,2-C(10)H(6)O(2) (1,2-naphthoquinone) + H. On the basis of this, the 1-naphthyl + O(2) reaction is concluded to form the following products (with the overall reaction energies given in parentheses): 1-naphthoxy + O (-15.5 kcal/mol), indenyl + CO(2) (-123.9 kcal/mol), 1-benzopyranyl + CO (-97.2 kcal/mol), and 1,2-naphthoquinone + H (-63.5 kcal/mol). The 2-naphthyl + O(2) reaction is predicted to produce 2-naphthoxy + O (-10.9 kcal/mol), indenyl + CO(2) (-123.7 kcal/mol), 2-benzopyranyl + CO (-90.7 kcal/mol), and 1,2-naphthoquinone + H (-63.2 kcal/mol). Simplified kinetic calculations using transition-state theory computed rate constants at the high-pressure limit indicate that the C(10)H(7)O + O product channels are favored at high temperatures, while the irreversible oxygen atom insertion first leading to the a10 and a10' or b10 and b10' intermediates and then to their various decomposition products is preferable at lower temperatures. Among the decomposition products, indenyl + CO(2) are always most favorable at lower temperatures, but the others, 1,2-C(10)H(6)O(2) (1,2-naphthoquinone) + H (from a10 and b10'), 1-C(9)H(7)O (1-benzopyranyl) + CO (from a10'), and 2-C(10)H(7)O (2-benzopyranyl) + O (from b10 and minor from b10'), may notably contribute or even become major products at higher temperatures.     

Theoretical study of mechanism of cycloaddition reaction between dimethylmethylenesilylene and formaldehyde

The mechanism of cycloaddition reaction between singlet dimethylmethylenesilylene and formaldehyde has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of different conformations are calculated by CCSD(T)//MP2/6‐31G* method. From the potential energy surface, it can be considered in thermodynamics and dynamics that reaction (1) and reaction (4) are the two dominant competitive reaction channels of cycloaddition reaction between dimethylmethylenesilylene and formaldehyde. The reaction process of reaction (1) is that: the two reactants (R1, R2) first form intermediates INT1a and INT1b through two reaction paths, a and b, which are barrier‐free exothermic reactions of 31.8 and 43.9 kJ/mol; then, INT1a and INT1b isomerize to a four‐membered ring product P1 via transition states TS1a and TS1b, with energy barriers of 26.3 and 24.4 kJ/mol. Reaction (4) also has two reaction paths, a and b, each of which consists of three steps are as follows: (i) the two reactants (R1, R2) first form intermediates INT3a and INT3b, which are barrier‐free exothermic reactions of 64.5 and 44.2 kJ/mol. (ii) INT3a and INT3b further react with formaldehyde (R2) to form intermediates INT4a and INT4b, through barrier‐free exothermic reactions of 22.9 and 22.2 kJ/mol. (iii) INT4a and INT4b then isomerize to form silapolycyclic product P4 via transition states TS4a and TS4b, with energy barriers of 39.7 and 29.3 kJ/mol. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

The reaction of o-alkynylarene and heteroarene carboxaldehyde derivatives with iodonium ions and nucleophiles: a versatile and regioselective synthesis of 1H-isochromene, naphthalene, indole, benzofuran, and benzothiophene compounds

The reaction of o-alkynylbenzaldehydes 1 with different alcohols, silylated nucleophiles 5, electron-rich arenes 10, and heteroarenes 12 in the presence of the reagent IPy(2)BF(4), at room temperature, gave functionalized 4-iodo-1H-isochromenes 2, 6, 11, and 13 in a regioselective manner. When alkynes 16 and alkenes 19 and 20 were used as nucleophiles, a regioselective benzannulation reaction took place to form 1-iodonaphthalenes 17 and 1-naphthyl ketones 18, respectively. Moreover, the latter process has been adapted to accomplish the synthesis of indole, benzofuran, and benzothiophene derivatives (23, 27, and 28, respectively). The three patterns of reactivity observed for the o-alkynylbenzaldehyde derivatives with IPy(2)BF(4) stem from a common iodinated isobenzopyrylium ion intermediate, A, that evolves in a different way depending on the nucleophile present in the reaction medium. A mechanism is proposed and the different reaction pathways observed as a function of the type of nucleophile are discussed. Furthermore, the reaction of the o-hexynylbenzaldehyde 1 b with styrene was monitored by NMR spectroscopy. Compound III, a resting state for the common intermediate in the absence of acid, has been isolated. Its evolution in acid media has been also tested, thereby providing support to the proposed mechanism.     

Thermodynamic properties of the species resulting from the phenyl radical with O2 reaction system

Phenyl radicals are formed in combustion and oxidation systems by abstraction of the phenyl—hydrogen from benzene or aromatics by active radical species and by oxidation and thermal reactions of the benzylic carbon on alkyl‐substituted aromatics. The reaction of phenyl with O₂ leads to chain‐branching reactions and a number of unsaturated oxygenated hydrocarbon intermediates that may need to be included in detailed combustion models. Thermochemical parameters and structures on important species resulting from the phenyl radical + O₂ association and reaction are reported in this study. Enthalpies, Δ_f H, of a series of stable molecules, radicals, and transition state structures are calculated using ab initio (G3MP2B3 and G3) and density functional (DFT, B3LYP/6–311g(d,p) calculations, group additivity (GA), and literature data. The ab initio and density functional calculations are combined with isodesmic reaction analysis, whenever possible, to improve the accuracy of the enthalpy values. Entropies, S, and heat capacities, Cp_f298 (T), are calculated using density functional calculations, group additivity, and literature data. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 583–604, 2008     

Intramolecularly Base-Coordinated Silylenes That Behave as Sila-Ylides

Divalent silicon species bearing an 8-amino- or 8-phosphino-1-naphthyl group have been shown to behave as nucleophilic sila-ylides in the presence of diphenylacetylene to afford zwitterionic intermediates containing alkenyl anion and ammonium or phosphonium cation moieties. The reaction pathways of these zeitterionic intermediates have been clarified to be highly dependent on the character of the cationic center such as N and P.     

Iron-catalyzed oxidation of thioethers by iodosylarenes: stereoselectivity and reaction mechanism

Catalytic properties of a series of iron(III)-salen (salen=N,N'-bis(salicylidene)ethylenediamine dianion) and related complexes in asymmetric sulfoxidation reactions, with iodosylarenes as terminal oxidants, have been explored. These catalysts have been found to efficiently catalyze oxidation of alkyl aryl sulfides to sulfoxides with high chemoselectivity (up to 100 %) and moderate-to-high enantioselectivity (up to 84 % with isopropylthiobenzene and iodosylmesitylene), the TON (TON=turnover number) approaching 500. The influence of the ligand (electronic and steric effects of the substituents), oxidant, and substrate structures on the oxidation stereoselectivity has been investigated systematically. The structure of the reactive intermediates (complexes of the type [Fe(III)(ArIO)(salen)] and the reaction mechanism have been revealed by both mechanistic studies with different iodosylarenes and direct in situ (1)H NMR observation of the formation of the reactive species and its reaction with the substrate.     

Pyrroles from ketoximes and acetylene. 40. Reaction of alkyl hetaryl ketoximes with 1,2-dichloroethane in superbase media

2-(2-Furyl)- and 2-(2-thienyl)pyrroles and their N-vinyl derivatives were synthesized by the reaction of alkyl furyl (thienyl) ketoximes with 1,2-dichloroethane in superbase media. 2-Chloroethyl and vinyl ethers of alkyl hetaryl ketoximes are intermediates in the reaction.See [1] for Communication 39.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 901–906, July, 1989.     

Investigations of Cylindrical Reaction Cavities from Ordered Phases of Alkyl Alkanoates and Their Influence on Some Norrish-Yang and Photo-Fries Reactions*

The Norrish-Yang photochemistry of three isomeric p-alkyl alkanophenones (p-propyl nonadecanophenone, p-pentyl heptadecanophenone and p-octyl tetradecano-phenone) and the photo-Fries reactions of 2-naphthyl myristate have been investigated in the ordered (layered) phases of three isomeric alkyl alkanoates. Comparisons of photoproduct selectivity for irradiation of one substrate in the isotropic and ordered phases of one host ester provide information concerning the influence of the cylindrically shaped reaction cavities on the relative motions and conformational changes necessary to convert the reactants to products. Comparisons of photoproduct distributions from one substrate in comparable phases of two or more esters provide details concerning the “wall stiffness” and importance of functional group interactions of the reaction cavities. Finally, comparisons using one substrate and two ordered phases of the same ester indicate the role of wall stiffness on photoproduct selectivity. The results show that the course of the photochemical reactions can be controlled effectively within the ordered media and provide an indication of how to design and select ordered media to effect other photochemical transformations selectively.     

Microwave Induced Conversion of Dialkyl 2-(3-Acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene)Butanedioates to Dialkyl 2-(3-Acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in the Presence of Silica Gel Powder in Solvent-Free Conditions

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 1-hydroxy-2-acetonaphthone leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates. Microwave was found to catalyze conversion of dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in the presence of silica gel powder in solvent-free conditions.     

The abnormal finkelstein reaction. A sequential ionic-free radical reaction mechanism

The reaction of alkyl halides with sodium iodide in acetone (Finkelstein Reaction) may yield coupled or rearranged products $\text{via}$ cationic intermediates.     

Chiral photochemistry within zeolites

Chiral induction of chemical reactions continues to be one of the main concerns of chemists. While basic rules of chiral induction of thermal reactions have been reasonably established, the same is not true of photochemical reactions. Short excited state lifetime and low activation energies for reactions in the excited state(s) leave very little room for manipulating the diastereomeric transition states. Yet impressive chiral induction of photochemical reactions in the solid state has been achieved. On the other hand, chiral induction of photoreactions of organic molecules in solution continues to be inefficient at ambient conditions. We are exploring the possibility of employing zeolites as a media for achieving chiral induction during photoreactions. The motivating force for such an attempt is the fact that chiral chemistry in the solid state is not completely general due to the fact that not all molecules crystallize. To achieve chiral induction one needs a chiral perturber. Zeolites are not chiral and therefore the perturber is added to the medium. Thus the medium for a photoreaction is a chirally modified zeolite. Of the several reactions investigated, results on photoelectrocylization of tropolone alkyl ethers are discussed at length. The confined space offered by the zeolite supercage forces a reactant and the chiral inductor to interact intimately to yield enantiomerically enriched product. Due to the transitory nature of the reaction cavity in solution such close interactions are less likely in isotropic solvent media. The examples discussed herein show negligible chiral induction in solution, whereas in a zeolite one obtains induction as high as 90%.     

Nickel-catalyzed migratory alkyl–alkyl cross-coupling reaction

The selective cross-coupling of activated electrophiles with unactivated ones has been regarded as a challenging task in cross-electrophile couplings. Herein we describe a migratory cross-coupling strategy, which can overcome this obstacle to access the desired cross-coupling products. Accordingly, a selective migratory cross-coupling of two alkyl electrophiles has been accomplished by nickel catalysis. Remarkably, this alkyl–alkyl cross-coupling reaction provides a platform to prepare 2°–2° carbon–carbon bonds from 1° and 2° carbon coupling partners. Preliminary mechanistic studies suggest that chain-walking occurs at both alkyl halides in this reaction, thus a catalytic cycle with the key step involving two alkylnickel(ii) species is proposed for this transformation.

The selective cross-coupling of activated electrophiles with unactivated ones has been regarded as a challenging task in cross-electrophile couplings.     

Base-mediated reaction of vinyl bromides with aryl azides: one-pot synthesis of 1,5-disubstituted 1,2,3-triazoles

A one-pot base-mediated reaction of azides and β- or α-vinyl bromides has been reported. The effects of bases and solvents have been investigated in the process. A variety of 1,5-disubstituted triazoles were prepared in low to good yields. Further studies reveal that the corresponding alkynes were produced as intermediates via elimination reaction. Under the same reaction conditions, the reactions of alkyl alkynes with phenyl azide would give 1,5-disubstituted 1,2,3-triazoles.     

Silica Gel Catalyzed Stereoselective Conversion of Dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to Dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in Solvent-Free Conditions

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 1-hydroxy-2-acetonaphthone leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates. Silica gel was found to catalyze conversion of dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in solvent-free conditions at 90°;C in fairly good yields.     

The kinetics of reaction of copper with substituted benzyl bromides in dipolar aprotic solvents

The reaction of copper with benzyl bromides in dipolar aprotic solvents has been studied. There are no linear or other simple relations between ε, 1/ε, Y, P, n, and the rate of reaction. The activity of the solvent is determined by donor number (DN) in reaction under consideration. The kinetic and thermodynamic parameters of the reaction of copper with benzyl bromide in dimethyl sulfoxide (DMSO) have been clarified. Hammett plots of log (k/k°) vs. the substituent constant σ gave good correlations (ρ = 0.18, S_ρ = 0.02, r = 0.961 in dimethyl sulfoxide and ρ = 0.21, S_ρ = 0.02, r = 0.947 in dimethylacetamide (DMAA)). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. The Hammett ρ value also depends on DN. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 496–501, 2005