Pd(II) acts simultaneously as a Lewis acid and as a transition-metal catalyst: synthesis of cyclic alkenyl ethers from acetylenic aldehydes

The reaction of carbon-tethered acetylenic aldehydes with alcohols in the presence of a catalytic amount of Pd(OAc)2 in 1,4-dioxane at room temperature gave the 5- or 6-membered acetal products in high yields. The 13C NMR studies suggested that a Pd(II) catalyst exhibited dual roles in the present reaction; the attack of ROH to aldehyde is catalyzed by Lewis acidic Pd(OAc)2, and the nucleophilic oxygen of the resulting hemiacetal reacts with alkyne complexed by Pd(II), giving the alkenyl ethers.     

Reactive diene for synthesis of substituted catechols

(2R,3R)-2,3-Dimethoxy-2,3-dimethyl-5,6-dimethylene-1,4-dioxane has been synthesized and is a highly efficient diene in Diels-Alder reactions. Reaction with acetylenic dienophiles provides a simple route to substituted catechols. Reactions with some ethylenic dienophiles are also reported.     

Infrared spectra of cyclic ethers and their derivatives

The IR spectra of six monosubstituted and of four 2,6-disubstituted 1,4-dioxanes have been studied in the 650–1800cm^–1 region. The assignment of the bands due to the vibrations of the 1,4-dioxane ring and to the deformation vibrations of the methylene groups of the ring is given. The appearance of a whole series of new absorption bands on passing from unsubstituted 1,4-dioxane to its derivatives is explained by the change in the symmetry of the molecule and the removal of the prohibition from the vibrations previously inactive in the IR spectra connected with this reduction in symmetry. It is proposed to use, in order to confirm the presence of a 1,4-dioxane ring in a molecule from the results of IR spectroscopy, not only the 1126-cm^–1 band but the whole group of bands lying in the frequency ranges 800–950, 1000–1150, and 1200–1300 cm^–1.For part I, see [3].     

Occurrence of 1,4-dioxane in cosmetic raw materials and finished cosmetic products.

Surveys of cosmetic raw materials and finished products for the presence of the carcinogen 1,4-dioxane have been conducted by the U.S. Food and Drug Administration since 1979. Analytical methods are described for the determination of 1,4-dioxane in ethoxylated cosmetic raw materials and cosmetic finished products. 1,4-Dioxane was isolated by azeotropic atmospheric distillation and determined by gas chromatography using n-butanol as an internal standard. A solid-phase extraction procedure based on a previously published method for the determination of 1,4-dioxane in cosmetic finished products was also used. 1,4-Dioxane was found in ethoxylated raw materials at levels up to 1410 ppm, and at levels up to 279 ppm in cosmetic finished products. Levels of 1,4-dioxane in excess of 85 ppm in children's shampoos indicate that continued monitoring of raw materials and finished products is warranted.     

Vinyl Ethers Containing an Epoxy Group: XXII. Synthesis and Base-Catalyzed Transformations of 1-(Allyloxy)- and 1-[2-(Vinyloxy)ethoxy]-3-(2-propynyloxy)propan-2-ols

Reactions of 2-(allyloxymethyl)- and 2-[2-(vinyloxy)ethoxy]methyloxiranes with 2-propynol (～3 wt % of t-BuOK, 75–85°C, 5–10 h) lead to formation of new 1-organyloxy-3-(2-propynyloxy)propan-2-ols (yield 65–95%). On heating to 45–100°C in the presence of bases (KOH, t-BuOK), 1-allyloxy- and 1-[2-(vinyloxy)ethoxy]-3-(2-propynyloxy)propan-2-ols are transformed into the corresponding 2-vinyl-1,3-dioxolane, 6-methyl-2,3-dihydro-1,4-dioxine, 6-methylene-1,4-dioxane, and 2,3-dihydro-5H-1,4-dioxepine derivatives, whose yield and ratio strongly depend on the solvent nature, catalyst, and substituent at the hydroxy group. 2-Vinyl-1,3-dioxolane and 6-methyl-2,3-dihydro-1,4-dioxine derivatives are formed as the major products (yield 70–99%) in the presence of t-BuOK in aprotic media (toluene, THF, DMSO) or in the absence of a solvent as a result of prototropic isomerization followed by intramolecular heterocyclization. Intramolecular nucleophilic cyclization of 3-(2-propynyloxy)propan-2-ols to 6-methylene-1,4-dioxane is the predominant process in water in the presence of KOH. In all cases, the fraction of 2,3-dihydro-5H-1,4-dioxepine derivatives among the cyclization products ranges from 0 to 5% (KOH) or to 14% (t-BuOK).     

Substitution of acetylenic groups for halogen in the quinonoid ring

The bromine or iodine atom in the quinonoid ring devoid of +M substituent in the position neighboring to the halogen is replaced by acetylenic groups on treatment with Cu^I acetylides, prepared either beforehand or in situ, in a mixture of DMSO and CHCl₃ in the presence of a Pd complex catalyst. A series of mono- and diacetylenic derivatives of 1,4-naphtho- and 1,4-benzoquinone were prepared. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1636–1639, July, 2005.     

Stereoselective synthesis of 2-alkenylaziridines and 2-alkenylazetidines by palladium-catalyzed intramolecular amination of alpha- and beta-amino allenes.

Whereas palladium-catalyzed reaction of N-arylsulfonyl-alpha-amino allenes with an aryl iodide (4 equiv) in the presence of potassium carbonate (4 equiv) in DMF at around 70 degrees C affords the corresponding 3-pyrroline derivatives, the reaction in refluxing 1,4-dioxane under otherwise identical conditions yields exclusively or most predominantly the corresponding 2-alkenylaziridines bearing an aryl group on the double bond. Similarly, N-arylsulfonyl-beta-amino allenes can be also cyclized into the corresponding alkenylazetidines bearing a 2,4-cis-configuration under palladium-catalyzed cyclization conditions in DMF.     

Formation of carbon-sulfur and carbon-selenium bonds by palladium-catalyzed decarboxylative cross-couplings of hindered 2,6-dialkoxybenzoic acids

A simple route to diaryl sulfides using a decarboxylative palladium-catalyzed reaction between electron-rich 2,6-dialkoxybenzoic acid derivatives and diaryl disulfides is reported. This coupling proceeds efficiently in the presence of Pd(CF(3)CO(2))(2) and Ag(2)CO(3) in a 65:1 mixture of 1,4-dioxane and tetramethylene sulfoxide (TMSO). We present also the first formation of a carbon-selenium bond via a palladium-catalyzed decarboxylative cross-coupling.     

Synthesis and Biological Activity of Cyanoethyl Derivatives of Fusidic Acid

3,11-Dihydroxy and 3,11-dioxo triterpenoids of the fusidane series reacted with acrylonitrile in 1,4-dioxane in the presence of alkali and phase-transfer catalyst to give mono- and bis(2-cyanoethoxy) and 2-cyanoethyl derivatives. The reaction with 3,11-dioxo analog afforded 2,2-disubstituted derivative as a result of addition of two cyanoethyl groups to the α-position with respect to the C³=O carbonyl group. The isolated compounds were screened for antibacterial and antifungal activities.

     

Organoboron compounds: CDXII. The synthesis of 2-substituted 1-iodo-1,4-pentadienes by iodination of 1,4-pentadienylboron derivatives

2-Substituted dimethoxy(1,4-pentadienyl)boranes, which are obtained by the condensation of triallylborane with acetylenic compounds followed by methanolysis, react with iodine in the presence of NaOH to form 2-substituted 1-iodo-1,4-pentadienes.     

Advances in chemistry in the benzo-1,4-dioxane series (review)

The literature data on methods for the preparation of benzo-1,4-dioxane derivatives and their chemical and physical properties, spectral characteristics, and biological activity are correlated.     

Improved Syntheses of Halofuranose Derivatives with the Desired α-Configuration

Chlorination of ribofuranose or 2-deoxyribofuranose derivatives was carried out in a 1,4-dioxane solution of hydrogen chloride. This improved procedure allowed the syntheses of 1-chloro-α-D -ribofuranose and 1-chloro-2-deoxy-α-D -ribofuranose derivatives and offered ease of handling, high yield, and the stereo-controlled α-configuration at C-I.     

Experimental determination and modeling of structure II hydrates in mixtures of methane+water+1,4-dioxane

Hydrate phase equilibrium conditions were measured with a Cailletet apparatus in the pressure range 2<14 MPa. The investigated 1,4-dioxane concentrations were 1, 2, 5, 7, 10, 20 and 30 mol% relative to water. The results show that adding 1,4-dioxane up to concentrations of 6 mol%, about the stoichiometric ratio of large sII cages to water (1/17), reduced the equilibrium pressure of hydrate formation. Adding 1,4-dioxane beyond 6 mol% caused a slow increase of the equilibrium pressures. The hydrate phase equilibria data were modeled as equilibrium between a liquid phase of water and 1,4-dioxane, with a small amount of methane, and a sII hydrate of 1,4-dioxane and methane. The chemical potential of the hydrate phase was described using the van der Waals and Platteeuw theory. Activity coefficients of the liquid phase were calculated by a van Laar relation, based on literature 1,4-dioxane+water VLE data. The predicted equilibrium pressures calculated were within 5% of the data up to a concentration of 20 mol% 1,4-dioxane relative to water.     

“LIVING-LIKE” CATIONIC POLYMERIZATION OF ISOBUTYL VINYL ETHER INITIATED BY CARBOXYL GROUPS ON CARBON BLACK SURFACE/ETHYLALUMINUM DICHLORIDE SYSTEM IN THE PRESENCE OF 1,4-DIOXANE

The effect of 1,4-dioxane as an added base on the cationic polymerization of isobutyl vinyl ether (IBVE) initiated by carboxyl groups on carbon black surface/ethylaluminum dichloride (EtAlCl₂) system was investigated. Although the cationic polymerization of IBVE by carbon black/EtAlCl₂ system the absence of 1,4-dioxane instaneously proceeded and the monomer conversion achieved 100% within a minute. The molecular weight distribution (MWD) of polyIBVE obtained was very broad. On the contrary, the MWD of polyIBVE obtained was very narrow and narrower than that obtained from the carbon black/ZnCl₂ initiating system by the addition of 1,4-dioxane. The number-average molecular weight (Mn) of polyIBVE obtained was directly proportional to monomer conversion in the cationic polymerization. However, the Mn of polyIBVE obtained from the polymerization by the initiating system in the the presence of 1,4-dioxane was smaller than that of the calculated value, assuming that polyl(IBVE) chain forms per unit carboxyl group on carbon black surface. It was concluded that carbon black/EtAlCl₂ initiating systems in the presence of 1,4-dioxane has an ability to initiate “living-like” cationic polymerization of IBVE based on the above results. PolyIBVE was grafted onto a carbon black surface after quenching the above “living-like” cationic polymerization systems with methanol.     

Synthesis and Stereochemistry of Some New 1,3-Dioxane Derivatives of 1,4-Diacetylbenzene

 The synthesis and stereochemistry of new 1,3-dioxane derivatives of 1,4-diacetylbenzene are reported. The anancomeric structure of these compounds, the axial orientation of the aryl group for both 1,3-dioxane rings, and the cis and trans isomerism of some of these compounds is discussed considering data of conformational analysis, NMR investigations, and single crystal X-ray diffractometry.     

Reaction of N,N'-Di(methoxycarbonyl)-p-benzoquinonediimine with Meldrum's Acid and its Analogs

Reactions of 2,2-dimethyl-4,6-dioxo-1,3-dioxane (Meldrum's acid), 2,2-tetramethylene-4,6-dioxo-1,3-dioxane and 2,2-pentamethylene-4,6-dioxo-1,3-dioxane in the presence of MeONa gave rise instead of expectable products of Michael 1,4-addition the corresponding N,N'-di(methoxycarbonyl)-p-benzoquinonediimines substituted in the ring.     

Antioxidant activity of uracil derivatives

The antiradical properties of a number of uracil derivatives are studied in initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the uracil derivatives as inhibitors is estimated. The antiradical activity of the compounds is quantitatively characterized in terms of the effective rate constant of inhibition, fk _In.     

Antioxidant properties of conjugates of triterpenic acids with amido derivatives of Trolox

The antioxidant properties of conjugates of betulonic and betulinic acids with amido derivatives of the acid Trolox were studied for initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the compounds was characterized in terms of the apparent inhibition rate constant fk _In.     

Synthesis of cyclic ethers from diols in the presence of copper catalysts

A number of cyclic ethers, namely tetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, oxepane, oxocane, and 1,4-oxathiane, have been synthesized in high yields by intramolecular dehydration of diols in the presence of copper-based catalysts.     

Synthesis and properties of diphenoxo-bridged CoII, NiII, CuII, and ZnII complexes of a new tripodal ligand: generation and properties of MII-coordinated phenoxyl radical species

Four dinuclear complexes of composition [MII2(L)2].xS [M=Co, x=0.5, S=1,4-dioxane (1.0.5 1,4-dioxane); Ni, x=0 (2) [single crystals have x=2, S=diethyl ether (2.2 diethyl ether)]; Cu, x=0 (3); Zn, x=0.5, S=1,4-dioxane (4.0.5 1,4-dioxane)] have been synthesized using a new tripodal ligand [2,4-di tert-butyl-6-{[(2-pyridyl)ethyl](2-hydroxybenzyl)-aminomethyl}-phenol (H2L)], in its deprotonated form, providing a N 2O 2 donor set. Crystallographic analyses reveal that the complexes have a similar diphenoxo-bridged structure. Each metal ion is terminally coordinated by 2,4-di tert-butyl-phenolate oxygen, a tertiary amine, and a pyridyl nitrogen. From each ligand, unsubstituted phenolate oxygen provides bridging coordination. Thus, each metal center assumes M (II)N 2O 3 coordination. Whereas the geometry around the metal ion in 1.0.5 1,4-dioxane, 2.2 diethyl ether and, 4.0.5 1,4-dioxane is distorted trigonal-bipyramidal, in 3 each copper(II) center is in a square-pyramidal environment. Temperature-dependent magnetic behavior has been investigated to reveal intramolecular antiferromagnetic exchange coupling for these compounds (-J=6.1, 28.6, and 359 cm(-1) for 1.0.5 1,4-dioxane, 2, and 3, respectively). Spectroscopic properties of the complexes have also been investigated. When examined by cyclic voltammetry (CV), all four complexes undergo in CH2Cl2 two reversible ligand-based (2,4-di tert-butylphenolate unit) one-electron oxidations [E1/2(1)=0.50-0.58 and E1/2(2)=0.63-0.75 V vs SCE (saturated calomel electrode)]. The chemically/coulometrically generated two-electron oxidized form of 3 rearranges to a monomeric species with instantaneous abstraction of the hydrogen atom, and for 4.0.5 1,4-dioxane the dimeric unit remains intact, exhibiting an EPR spectrum characteristic of the presence of ZnII-coordinated phenoxyl radical (UV-vis and EPR spectroscopy). To suggest the site of oxidation (metal or ligand-centered), in each case DFT calculations have been performed at the B3LYP level of theory.