Elimination Of Hydrogen Halide Research Articles

One‐Pot Synthesis of Fused Indolin‐3‐Ones via a [3+3] Cycloaddition Reaction

AbstractA formal [3+3] cycloaddition reaction of azaoxyallyl cations and isatogens generated in situ from α‐halo hydroxamates and o‐nitroalkynes, respectively, was developed. The cycloisomerization of the o‐nitroalkynes, followed by base‐mediated elimination of hydrogen halide and 1,3‐dipolar cycloaddition of the azaoxyallyl cations with the isatogen intermediates, were hallmarks of this one‐pot tandem reaction. A series of tricyclic fused indolin‐3‐ones were obtained under very mild reaction conditions with high atom economy, and the reaction exhibited excellent functional group tolerance. In addition, the reaction was highly scalable to multigram quantities. The obtained indolin‐3‐ones exhibited robust DNA staining patterns in agarose gel electrophoresis. Coupled with the fluorescence properties of the products, these results highlight the potential utility of tricyclic fused indolin‐3‐ones in various fluorescence and cell‐staining applications.magnified image

The synthesis of new pyrrolo[2,3-d]pyrimidine-containing α-hydroxyphosphonic acids

The work is devoted to the synthesis of new pyrrolo[2,3-d]pyrimidine-containing α-hydroxyphosphonic acids as precursors for the synthesis of potential biologically active compounds. The reaction between methyl 7-allyl-1,3dimethyl-2,4-dioxo-2,3,4,7-tetrahydro-1Н-pyrrolo[2,3-d]pyrimidine-6-carboxylate and iodine has resulted in 8-iodomethylpyrimido[5’,4’:4,5]pyrrolo[2,1-c][1,4]oxazine. The composition and structure of the compound has been confirmed by elemental analysis, NMR-spectroscopy and X-ray examination, and it is a convincing evidence of the presence of the oxazine cycle. Elimination of hydrogen halide of the iodomethyl derivative occurred with formation of 1,3,8-trimethyl-2H-pyrimido[5’,4’:4,5]pyrrolo[2,1-c][1,4]oxazine-2,4,6(1H,3H)-trione. The compound obtained upon heating with methanol in the presence of potassium carbonate was subjected to the nucleophilic attack at the carbonyl group. 7-(2-Oxopropyl)-1H-pyrrolo[2,3-d]pyrimidine derivative was formed by cleavage of the lactone ring. The treatment of ketone with diisopropyl phosphite by Abramov reaction resulted in formation of pyrimido[5’,4’:4,5] pyrrolo[2,1-c][1,4]oxazin-8-ylphosphonate, its hydrolysis was carried out by boiling in dilute hydrochloric acid. The reaction proceeded by opening of the oxazine ring, with the concomitant decarboxylation giving pyrrolo[2,3-d] pyrimidine with the 1-hydroxyphosphonoethyl substituent in position 7 of the heterocycle. The structure of the compounds obtained has been proven using NMR spectroscopy, mass-spectra and elemental analysis.

ChemInform Abstract: Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

AbstractReview: 43 refs.

Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re3Cl9, the cluster framework is stable at least up to 300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses.

A facile synthesis of the novel thiazolo[3,2-a]pyrimidine derivatives

2-Bromomethyl- and 2-iodomethyl-2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones are prepared via the reaction of 3-allyl-2-thiouracil derivatives with bromine or iodine chloride, respectively. The 6-bromo and 6-nitro derivatives are synthesized by an electrophilic substitution at C-6 of the thiazolopyrimidine system. As a result, novel 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one derivatives are obtained. Hydrogen halide elimination from the 2-halomethyl-2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones is also reported.

Concerted and sequential pathways of proton-coupled electron transfer in hydrogen halide elimination

Proton-coupled electron transfer (PCET) is a key reaction in a diverse array of chemical and biochemical processes. Concerted PCET, a single step process where no intermediates are expected, is often difficult to distinguish from sequential electron transfer/proton transfer (or proton transfer/electron transfer) events that involve one or more reactive intermediates. Here we demonstrate that in an apparently simple and fundamental organic reaction, hydrogen halide elimination (dehydrohalogenation), both mechanisms occur, with concerted PCET kinetically favored over sequential ET/PT. The latter involves a well-defined reactive intermediate, the corresponding iso-halon.

A gas-phase kinetic study on the thermal decomposition of 2-chloropropene

The gas-phase thermal decomposition of 2-chloropropene in the presence of a radical inhibitor was studied in the temperature range of 668.2–747.2 K and pressure between 11–76 Torr using the conventional static system. The dehydrochlorination to propyne and HCl was the only reaction channel and accounted for >98% of the reaction. The formation of propyne was found to be homogeneous and unimolecular and follows a first-order rate law. The observed rate coefficient is expressed by the following Arrhenius equation: $$ k_{total} = 10^{13.05 \pm 0.46} (s^{ - 1} )\exp ^{ - 242.6 \pm 6.2({{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}})/RT} . $$ The hydrogen halide elimination is believed to proceed through a semipolar four-membered cyclic transition state. The presence of a methyl group on the α-carbon atom lowered the activation energy by 47 kJ mol−1. The experimentally observed pressure dependence of the rate constant is compared with the theoretically predicted values that are obtained by RRKM calculations.

β-Mercaptoalkanoic carboxylic esters: versatile synthons in heterocyclic chemistry

This review presents approaches to the synthesis of heterocyclic annelated thiophenes of the last 35 years. Annelated thiophenes have been reported by the cyclocondensation reaction of β -mercaptoalkanoic carboxylic esters with 1,3-bifunctional substrates such as α -haloenones, β -haloenones, α -halogenoacrylic acid derivatives. The reaction takes place by nucleophilic addititon, followed by Dieckmann cyclization with the elimination of hydrogen halide. In case of other substrates such as β -chlorocinnamonitriles, β -haloacrylonitriles, arylsulfonylacrylonitriles, α,β -unsaturated nitriles, Dieckmann–Thorpe–Ziegler cyclization occurs resulting in aminothiophene derivatives. Functionalized annulated thiophene derivatives have potent industrial applications because of significant biological properties. Dedicated to Dr. C. Someswara Rao on the occasion of his 72nd birthday

Thermodynamics of thermal decomposition of group 13 metal trihalide adducts with piperidine: A combined theoretical and experimental study

Three major decomposition pathways of complexes formed by MX 3 (M = Al, Ga; X = Cl, I) and piperidine (pip) have been theoretically considered at the B3LYP/LANL2DZ(d,p) level of theory. Hydrogen gas elimination with formation of gaseous MX 3 · pyridine complexes becomes thermodynamically favorable above 500 K and is expected as a primary thermolysis product of MX 3 · pip. Alternative routes, which include dissociation into components or hydrogen halide elimination, require much higher temperatures, despite of the exothermic dimerization energies of the MX 2C 5H 10N monomers. This theoretical conclusion is in qualitative agreement with present experimental thermolysis study of the GaCl 3 · pip complex.

One or More C:C Bond(s) by Elimination of Hydrogen, Carbon, Halogen, or Oxygen Functions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Quantum chemical investigations on the dynamics of hydrogen halide elimination from vinyl-halides: influence of the molecular environment

The dynamics of three-center vs four-center dissociative reactions of vinyl-halides was investigated theoretically by Langevin molecular dynamics method in the absence and in the presence of frictional interaction between the molecules and their environment. The results show a redistribution of the vibrational energy on the bonds of vinyl-halide molecules under the effect of frictional interaction. This redistribution modifies the reaction rates of the dissociation channels. The above unexpected phenomenon is most pronounced in case of vinyl-iodide and shows a slight decrease by moving towards vinyl-fluoride. It has been shown, that the existence of friction may not guarantee statistical behaviour of the dissociation processes of these asymmetrically substituted olefins.

A Convenient One‐Pot Synthesis of Homoallylic Halides and 1,3‐Butadienes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A convenient one-pot synthesis of homoallylic halides and 1,3-butadienes

An efficient one-pot synthetic pathway for the preparation of homoallylic halides by in situ generated MgBrCl-promoted ring opening of cyclopropylcarbinyl acetates has been established. An easily accessible one-pot synthetic protocol of 1,3-butadienes by the elimination of hydrogen halides from the resulting homoallylic halides in the presence of an excess amount of strong base has also been developed.

Quantum-Chemical Study of Silicon Halide Adducts with Nitrogen-containing Donors: III. Energy Effects of Ammonolysis and Complex-Formation Reactions in Silicon Tetrahalide-Ammonia Systems

Thermodynamic characteristics of hydrogen halide elimination from SiX4-NH3 systems were calculated by the B3LYP density functional method. The role of adducts and oligomeric forms of compounds containing Si-N bonds, as intermediates in the chemical vapor deposition of silicon nitride, was considered. It was shown experimentally that the reaction between silicon tetrachloride and ammonia in nonaqueous solvents involves ammonolysis.

Sodium hydride/hexamethylphosphoric triamide: a new and efficient reagent towards the synthesis of protected 1,2- and 5,6-enopyranosides

A new method for the elimination of hydrogen halides and p-toluenesulfonic acid from sugar moieties using sodium hydride (NaH) in hexamethylphosphoric triamide (HMPA) at room temperature is reported. NaH/HMPA has several advantages compared to NaH/DMF: elimination products are produced in high yields even from sterically hindered starting materials, and not only from halides, but also tosylates.

Structural and Thermodynamic Characteristics of Compounds X2MYH2 (M = Al, Ga, In; X = F, Cl, Br, I; Y = N, P, As) Formed by Hydrogen Halide Elimination from Donor-Acceptor Complexes X3MYH3

Geometry and thermodynamic characteristics of complexes X2MYH2 (M = Al, Ga, In; X = F, Cl, Br, I; Y = N, P, As) and their components were found by the B3LYP density functional method with the LANL2DZ(d,p) basic set. The nitrogen complexes X2MNH2 have a planar structure, whereas the phosphorus and arsenic complexes are pyramidal. Upon HX elimination, the dissociation energy of the M-Y bonds considerably increases (by 150-270 kJ mol-1), which makes the dissociation of X2MYH2 into components thermodynamically unfeasible even at temperatures about 1000°C. A linear correlation between the dissociation enthalpies of M-Y bonds in the X3MYH3 and X2MYH2 complexes was found for each central atom M, which makes it possible to estimate the dissociation enthalpies of coordination-unsaturated compounds of the Group IIIa elements from the dissociation enthalpies of their coordination-saturated analogs. The enthalpies of dimerization of X2MYH2 fall in the range from 40 (Y = P, As) to 260 kJ mol-1 (Y = N), which makes the process X3MNH3 = [X2MNH2]2 + HX with the retention of the metal-nitrogen bond more favorable than the dissociation of the initial complex into the components. Thus, dimers [X2MNH2]2 can be intermediates in chemical deposition of nitrides from the gas phase of donor-acceptor complexes.

An investigation of a palladium catalysed biaryl synthesis of pyrrolophenanthridine derivatives. Extension of the Heck reaction

N-Benzylisatin derivatives have been found to readily undergo cyclisation via hydrogen halide elimination in a biaryl synthesis reaction when using palladium catalysts, in the absence of phosphine ligands, to yield oxopyrrolo[3,2,1-de]phenanthridine derivatives.

Chemical dehydrohalogenation of poly(ethylene-alt-chlorotrifluoroethylene)

Abstract Chemical dehydrohalogenation of poly(ethylene- alt -chlorotrifluoroethylene) (PE- a -CTFE) has been studied as a possible route to carbyne. The reaction products have been characterized by infrared and 13 C solid-state nuclear magnetic resonance spectroscopy. The dehydrohalogenation of PE- a -CTFE by potassium tert -butoxide in tetrahydrofuran has been shown to result in the formation of a halogen-substituted polyenyne structure with randomly distributed isolated triple bonds. The incomplete elimination of hydrogen halides can be explained by insufficient strength of the base, sterical hindrances caused by its bulkiness as well as by alternation defects in the original copolymer.

Alkylation and arylation of pyrazoles under solvent‐free conditions: Conventional heating versus microwave irradiation

AbstractThe use of sodium hydrogen carbonate under solvent‐free conditions and microwave irradiation is by far the best method for N‐alkylating pyrazoles. The yields are good and the method is devoid of side reactions (quaternization, isomerization, hydrogen halide elimination). Solvent‐free conditions are the only ones that allow us to prepare 1‐substituted pyrazoles from secondary halides. The procedure using quaternary salts in one‐pot provides an interesting alternative for the preparation of 1‐heteroarylpyrazoles.

Photophysics and photochemistry of sterically strained α-haloanthraquinones: The bromo and/or chloro substituted compounds

The steric hindrance between the oxygen and halogen atoms results in the structural deformation of α-haloanthraquinones and their lowest excited triplet (T 1 ) states are of mixed nπ*-ππ* or ππ* character with unusually short lifetimes. Moreover, the rates of hydrogen-atom abstraction from ethanol by the T, states decrease with their increasing ππ* character, and the proximity of the halogen atom to the hydroxy group causes the photochemical intramolecular elimination of hydrogen halide from the initial photoproducts (α-haloanthrahydroquinones) yielding α-haloanthraquinones (or anthraquinone) with one less halogen atom than the original molecule; the final product is anthrahydroquinone. The remarkably large structural deformation of 1,8-dihaloanthraquinones, furthermore, makes it possible to observe an absorption band due to a complex of two 1,8-dihaloanthrasemiquinone radicals which gives rise to the simultaneous formation of 1,8-dihaloanthrahydroquinones and the original anthraquinones. Of particular interest is observation of the absorption band(s) attributable to the second excited triplet (T 2 ) states of 1,8-dihaloanthraquinones. However, the electron transfer from triethylamine (TEA) to these T 2 states generating the radical anions is observed only in acetonitrile, while that to the T 1 states generating their exciplexes with TEA is observed not only in acetonitrile but also in toluene and ethanol.