Haloamidation of alkynes and related reactions using zirconacycles and isocyanates

Zirconacyclopentenes reacted with isocyanates to give aza- or oxazirconacycles which were conveniently coverted into the corresponding haloamidation products of alkynes after halogenation. 1,4-Bistrimethylsilyl substituted zirconacyclopentadiene afforded a low yield of iodoamidation product, whereas zirconium-alkyne complexes stabilized with phosphine gave the iodoamidation products in moderate yields. On the other hand, zirconacyclopentanes reacted with isocyanates to give trimerization products of isocyanate, isocyanurates.     

One-pot synthesis of functionalized hydantoin derivatives via a four-component reaction between an amine, an arylsulfonyl isocyanate and an alkyl propiolate or dialkyl acetylenedicarboxylate in the presence of triphenylphosphine

An effective route to functionalized hydantoin derivatives is described, involving the reaction of a urea derivative resulting from the addition of a primary amine to an arylsulfonyl isocyanate, and an alkyl propiolate or dialkyl acetylenedicarboxylate in the presence of triphenylphosphine. The reactive 1:1 intermediate obtained from the addition of triphenylphosphine to the alkyl propiolate or dialkyl acetylenedicarboxylate was trapped by NH-acids such as the urea derivative to produce functionalized hydantoin derivatives.     

Silicaphosphine (Silphos): a filterable reagent for the conversion of alcohols and thiols to alkyl bromides and iodides

Silicaphosphine (Silphos), [P(Cl)_3−n(SiO₂)_n], as a new heterogeneous reagent is introduced. This reagent converts alcohols and thiols to their corresponding bromides and iodides in the presence of X₂ (X=Br, I) in refluxing CH₃CN in high to quantitative yields. Use of Silphos provides a highly practical method for the easy separation of the Silphos oxide byproduct by a simple filtration.     

Effect of temperature on the mechanism of retention of fullerenes in liquid chromatography using various alkyl bonded stationary phases

Summary The temperature-dependency of the separation of fullerenes in liquid chromatography (LC) has been examined using various alkyl bonded stationary phases. It has been found that a maximum retention temperature exists with long alkyl bonded stationary phases, whereas there is no similar effect with the newly synthesized alkyl bonded phases which have two phenyl groups at the base of the bonded phase. The interpretation of the retention behavior of fullerenes in the low temperature region on alkyl bonded stationary phases is discussed using information obtained by CP-MAS solid-state NMR spectroscopy and LC.     

A theoretical study of the ion pair SN2 reaction between lithium isocyanates with methyl fluoride with inversion and retention mechanism

This paper is devoted to a detailed theoretical study of an ion pair S_N2 reaction LiNCO+CH₃F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state.     

Practical and general method for the direct synthesis of alkyl fluorides from alcohols under mild conditions: a reinvestigation

Abstract  In contrast to the results presented in a previous report, the direct conversion of alcohols to alkyl fluorides with triphenylphosphine and potassium fluoride in CCl₄/DMF under mild conditions failed. Graphical Abstract        

Glassy carbon modified by a silver-palladium alloy: cheap and convenient cathodes for the selective reductive homocoupling of alkyl iodides

Micrometer-thick layers of silver-palladium alloy were elaborated in order to modify the surface of glassy carbon electrodes. Such a surface modification can be readily achieved via a preliminary silver galvanostatic deposit onto carbon followed by a ‘palladization’ step, thanks to a simple immersion in acidic Pd^II-based solutions producing a displacement reaction. The as-prepared metallic interfaces exhibit outstanding catalytic capabilities especially in the cleavage of carbon-halogen bonds while being chemically/electrochemically quite stable and relatively inexpensive. More specifically, the use of such glassy carbon/Ag-Pd electrodes in dimethylformamide (DMF) containing tetraalkylammonium salts (TAA⁺X⁻) makes the one-electron reductions of primary alkyl iodides possible; this reduction leads to the formation of homodimers in high yields. Formation of a free radical as transient resulted from the homocoupling reaction.     

Efficient preparation of dichloromethyl alkyl ethers and their application in the formylation of aromatic compounds: Scope and limitations

Practical preparations of dichloromethyl alkyl ethers are described, based on the reaction of alkyl formates with oxalyl chloride in the presence of N-methylformanilide. The method involves a simple procedure that does not require the use of harmful reagents. Dichloromethyl propyl and dichloromethyl butyl ethers represent secure synthetic equivalents to dichloromethyl methyl ether. Formylations of both electron-deficient and electron-rich aromatics with these dichloromethyl alkyl ethers in the presence of AlCl₃, FeCl₃, or TiCl₄ have been systematically investigated. A plausible mechanism of formylation is discussed.     

A synthesis of isoxazoles through the reaction of activated acetylenes and alkyl 2-nitroethanoates in the presence of triphenylphosphine

The reaction of dialkyl acetylenedicarboxylates or dibenzoylacetylene with alkyl 2-nitroethanoates in the presence of triphenylphosphine leads to functionalized isoxazoles in good yields.     

Peculiarities of the mechanism of chlorotropic and conformational isomerism in a series of chloromethyl isocyanates

The thermodynamic and kinetic stability of chlorotropic isomers in a series of chloromethyl isocyanates Cl_3−nH_nC−N=C=O, where n=0, 1, 2, has been shown by quantum chemical calculations, using the MNDO method, and by³⁵Cl NQR spectroscopy. The phase transformations of two polymorphic modifications of N-chlorocarbonyl dichloride, which is a stable iminocarbonyl form of trichloromethyl isocyanate with small conformational activation barriers, have been studied. Institute of Bioorganic and Petrochemistry, National Academy of Sciences of Ukraine, 1 Murmansk ul., Kiev-94 252660, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 164–169, May–June, 1998.     

Haval-Argade contrathermodynamic rearrangement of alkylidenesuccinimides to alkylmaleimides via the corresponding isoimides: a general approach to alkyl and dialkyl substituted maleimides

A simple and efficient access to alkyl and dialkyl substituted maleimides has been demonstrated via the new contrathermodynamic rearrangement of (E)-alkylidenesuccinimides to alkylmaleimides. The (E)-alkylidenesuccinimides obtained from the Wittig-condensation of N-arylmaleimide with aliphatic aldehydes on regioselective hydrolysis furnished the corresponding (E)-alkylidenesuccinanilic acids in 95-98% yields. The β-alkylidenesuccinanilic acids on treatment with cyanuric chloride in the presence of triethylamine gave the corresponding β-alkylisomaleimides in 78-80% yields via the β-alkylideneisosuccinimides with the exocyclic to endocyclic carbon-carbon double bond migration. The kinetically controlled products alkylisomaleimides in refluxing acetic acid furnished the thermodynamically controlled alkylmaleimides in 98% yield. The Wittig condensation of alkyl substituted isomaleimides/maleimides with aliphatic aldehydes gave the desired dialkyl substituted maleimides in high yields. A conversion of α-methylenesuccinanilic acids to α-methylisomaleimides has also been described, with 90% yield.     

Synthesis of 4H-chromene derivatives by reaction between alkyl isocyanides and dialkyl acetylenedicarboxylate in the presence of 6-hydroxyquinoline

The reactive intermediate generated by the addition of alkyl isocyanides to dialkyi acetyienedicarboxyiate was trapped by 6- quinolinol to produce highlyfunctionalized 4H-chromenes in fairly good yields.     

An evaluation of phosphine and carbene adducts of phosphite- and phosphinite-based palladacycles in the coupling of alkyl bromides with aryl boronic acids

A range of palladacyclic catalysts and their phosphine and carbene adducts were tested in the Suzuki coupling of an alkyl bromide with phenylboronic acid and showed modest activity in some cases. Unlike with aryl halide substrates it appears that there is no particular benefit in the use of palladacycles as the palladium source. Initial data indicate that the rate determining step is not the oxidative addition of the alkyl halide substrate, but rather lies later in the catalytic cycle.     

Molecularly imprinted SPE coupled with HPLC for the selective separation and enrichment of alkyl imidazolium ionic liquids in environmental water samples

A novel 1‐butyl‐3‐methylimidazolium chloride ionic liquid surface imprinted solid‐phase sorbent was synthesized. The as‐prepared material was characterized by SEM, Brunauer–Emmett–Teller surface area analysis and Fourier Transform IR measurements. Then its adsorption properties for alkyl imidazolium ionic liquids, including adsorption capacities, adsorption kinetics, and properties of selective separation and enrichment were studied in detail. It was shown that the ionic liquid surface imprinted polymer exhibited high selective recognition characteristics for the imidazolium chloride ionic liquids with short alkyl chains (C_nmimCl, n = 2, 4, 6, 8) and the adsorption equilibrium was achieved within 25 min. Various parameters were optimized for the 1‐butyl‐3‐methylimidazolium chloride ionic liquid surface imprinted polymer SPE column, such as flow rate, eluent solvent, selectivity, and reusability of the column. Then, the SPE column coupled with HPLC was used for the determination of alkyl imidazolium ionic liquids. Experimental results showed that the existence of their structural analogs and common concomitants in environmental matrices did not affect the enrichment of 1‐butyl‐3‐methyl imidazolium chloride ionic liquid. The average recoveries of 1‐butyl‐3‐methylimidazolium chloride ionic liquid in spiked water samples were in the range of 92.0–102.0% with the RSD lower than 5.8%.     

Gas-phase reaction: alkyl cation transfer in the dissociation of protonated pyridyl carbamates in mass spectrometry

In the mass spectrometry of pyridyl carbamates, alkyl cation transfer is one of the major fragmentation reactions of the protonated molecules. Literature results and theoretical calculations indicate that the pyridine nitrogen is the most favorable site for protonation in these structures. Substituent and comparison experiments run to elucidate the fragmentation patterns reveal that the proton is localized at the pyridine nitrogen and the reaction center is charge-remote when the alkyl cation transfer occurs. The mechanism involving configuration inversion via an ion-neutral complex is favorable in energy for the alkyl cation transfer in these structures.     

Development of a fabric phase sorptive extraction with high‐performance liquid chromatography and ultraviolet detection method for the analysis of alkyl phenols in environmental samples

A novel analytical method has been developed and validated for the quantification of alkyl phenols in aqueous and soil samples. Fabric phase sorptive extraction, a new sorptive microextraction technique, has been employed for the preconcentration of some endocrine‐disruptor alkylphenol molecules, namely, 4‐tert‐butylphenol, 4‐sec‐butylphenol, 4‐tert‐amylphenol, and 4‐cumylphenol, followed by high‐performance liquid chromatography with ultraviolet detection. Various parameters influencing the fabric phase sorptive extraction performance, namely, extraction time, eluting solvent, elution time and pH of the sample matrix, were optimized. The chromatographic separation was carried out with a mobile phase of acetonitrile/water (60:40 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed‐phase C₁₈ column at λ_max 225 nm. The calibration curves of target analytes were prepared in the concentration range 5–500 ng/mL with good coefficient of determination values (R² > 0.992). Extraction efficiency values were 74.0, 75.6, 78.0, and 78.3 for 4‐tert‐butylphenol, 4‐sec‐butylphenol, 4‐tert‐amylphenol, and 4‐cumylphenol, respectively. The limits of detection range from 0.161 to 0.192 ng/mL. Subsequently, the new fabric phase sorptive extraction with high‐performance liquid chromatography and ultraviolet detection was successfully applied for the recovery of alkyl phenols from spiked ground water, river water, and treated water from a sewage treatment plant, and soil and sludge samples.     

Palladium(0)-catalyzed trimerization of arylisocyanates into 1,3,5-triarylisocyanurates in the presence of diimines: a nonintuitive mechanism

We show here that palladium(0) (dibenzylideneacetone) complexes bearing 1,10-phenanthroline constitute efficient catalysts for the cyclotrimerization of aromatic isocyanates. For the first time, the mechanism of this reaction has been investigated experimentally and theoretically with group 10 catalysts. This investigation provides a very consistent picture of the catalytic cycle. Notably, we establish that the reaction does not proceed by stepwise cycloadditions or ring insertions involving metallacyclic intermediates, as might have been anticipated. Rather, in our proposal, the initial steps of the mechanism resemble the chain-growth process operative during the anionic polymerization of isocyanates and feature charge-separated intermediates. These steps are then followed by ring closure on the metal center of the last intermediate formed to yield a seven-membered metallacycle that reductively eliminates the cyclotrimer and re-forms the active species. In addition, we conclusively show that the (known) palladacycles that could be isolated during the experimental investigations are not catalytic intermediates but result from catalyst deactivation. Thus, with Pd(0) diimine catalysts, the actual trimerization mechanism appears to be a blend between the two types of mechanisms proposed thus far for the oligomerization of heterocumulenes with very different catalysts. In conclusion, this work contributes to a better understanding of the reactivity of arylisocyanates in the vicinity of late group 10 metal centers in low oxidation state and sheds some light on the detrimental self-poisoning processes observed during the reductive carbonylation of nitroaromatic substrates catalyzed by related catalysts in non-nucleophilic media.     

The effect of nature and number of alkyl groups in tetraalkyl ammonium cations acting as templates during the synthesis of ZSM-5

Computer simulation studies have been applied to investigate the effect of alkyl groups in the structure directing property of the tetraalkyl ammonium cations (TAA) acting as templates during the synthesis of ZSM-5. The interaction between the model compounds has been studied to mimic the alkyl groups of the template molecule and the ZSM-5 framework as the nature and number of alkyl groups vary. Different cluster models were considered to study the extent of interaction with model compounds. The results of MNDO calculations show that the efficiency of TAA as template is dependent on the number and nature of alkyl groups present in them. The procedures used can successfully identify optimum templates for a given host and have applications in the synthesis of new microporous materials.