Showing papers in "Monatshefte Fur Chemie in 2005"
TL;DR: In this article, an experimentalist approaching theory for an understanding of conceptual chemistry that can be related to measurable properties, focuses on the electron density distribution, focusing on the definition of an atom, of the bonding between atoms, and of the boundary condition for the extension of quantum mechanics to an open system.
Abstract: An experimentalist approaching theory for an understanding of conceptual chemistry that can be related to measurable properties, focuses on the electron density distribution. One finds in the topology of the electron density the definition of an atom, of the bonding between atoms, and of the boundary condition for the extension of quantum mechanics to an open system – to an atom in a molecule. This paper describes this approach, as it evolved from the failure of existing models to a study of molecular charge distributions and of how these studies resulted in the extension of quantum mechanics to an open system using the action principle.
197 citations
TL;DR: In this paper, a convenient synthesis of zeolite L is presented, where the size of the crystals can be tuned between 30 and 6000nm, spanning a volume range of seven orders of magnitude.
Abstract: A convenient synthesis of zeolite L is presented. The size of the crystals can be tuned between 30 and 6000 nm, spanning a volume range of seven orders of magnitude. The zeolite L crystals, which typically feature a cylindrical morphology, are synthesized with various aspect ratios ranging from elongated to disc-shaped. The importance of obtaining zeolite crystals with well-defined size and morphology is discussed in view of potential applications of zeolite L containing organic dye molecules as guests.
170 citations
TL;DR: In this paper, the synthesis of different polymerisable ormocers for dental composites is reviewed in the second part of this paper, and the synthesis results on organosols are presented in this paper.
Abstract: Dental composite filling materials are improved by incorporating nanofillers. They impart increased hardness and wear resistance to composites. In addition, they produce better polishing results than macrofillers. If the particles are sufficiently small, transparent composite pastes are obtainable, independent of the refractive index of the polymerisable monomers. In this context, organosols, non-agglomerated nanoparticles in organic liquid media, are especially interesting. Some of our own results on organosols are presented in this paper. Their relatively low viscosity enables the preparation of composites with a high filler load, thus reducing the shrinkage of the dental composite during polymerisation and improving the mechanical properties. Inorganic–organic hybrids are an attractive class of materials for dental fillings. The synthesis of different polymerisable ormocers for dental composites is reviewed in the second part. Ormocers can be applied as a polymerisable matrix, improving biocompatibility and wear resistance. Their use as inorganic fillers improves the thermodynamic compatibility of the filler with the matrix and enhances the polishability. Functionalised inorganic clusters used as new additives combine the properties of very small nanoparticulate fillers and well-designed highly functional monomers with high crosslinking capabilities. Xerogel colour pigments are advantageous alternative additives to conventional pigments. 3-D structural colour pigments, which are obtained by the self-assembly of monodisperse spherical particles, produce an opalescent effect resembling that of the natural enamel in highly aesthetic composites.
152 citations
TL;DR: The purpose of the topological theory of Chemical Bonding is to provide a mathematical bridge between chemical concepts, such as bonds and lone pair, and rigorous Quantum Mechanics as discussed by the authors, and the theory of dynamical systems enables to achieve a partition of the geometrical molecular space into basins of attractors bearing a chemical significance.
Abstract: The purpose of the topological theory of Chemical Bonding is to provide a mathematical bridge between chemical concepts, such as bonds and lone pair, and rigorous Quantum Mechanics. The theory of dynamical systems enables to achieve a partition of the geometrical molecular space into basins of attractors bearing a chemical significance. A one to one correspondence is established between these basins and the chemical objects used to describe the bonding. The definition of population operators gives access to quantitative information and provides a firm basis for the concept of mesomery.
118 citations
TL;DR: In this paper, a molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic π-electron systems can be estimated.
Abstract: The fact that cyclic arrangements of double bonds have a dramatic effect on the behavior of conjugated organic molecules is known since the 19th century. The fact that in monocyclic conjugated systems the size of the cycle and the number of π-electrons involved is decisive for their stability (“aromaticity”) or lack of stability (“antiaromaticity”) is known since the 1930s. In polycyclic π-electron systems several cyclic effects are present simultaneously and their separation became possible only recently. A molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic π-electron systems can be estimated. This method is briefly outlined and illustrated by pertinent examples. An exhaustive bibliography of the topic considered is given.
75 citations
TL;DR: In this paper, a catalytic system for the selective oxidation of primary alcohols to aldehydes under very mild conditions was developed, which is based on TEMPO and Cu(II), which is generated in situ by oxidation of elemental copper and chelated by means of 2,2′-bipyridine.
Abstract: A catalytic system for the selective oxidation of primary alcohols to aldehydes under very mild conditions was developed. The catalytic system is based on TEMPO and Cu(II), which is generated in situ by oxidation of elemental copper and chelated by means of 2,2′-bipyridine. Compared to existing Cu/TEMPO oxidation methods we substantially lowered the amount of copper necessary and discovered that the reaction is dependent on pH. The catalytic system was also tested with polymer-bound TEMPO and new insights into the currently discussed mechanism were derived.
59 citations
TL;DR: In this paper, the authors give an overview of how catalytic coatings are applied in diesel particulate filter systems to support filter regeneration by soot oxidation with nitrogen dioxide or oxygen.
Abstract: This paper will give an overview how catalytic coatings are applied in diesel particulate filter systems to support filter regeneration by soot oxidation with nitrogen dioxide or oxygen. Catalytic coatings can be placed on a catalyst substrate in front of a diesel particulate filter, on a filter, or in a combined system on both. Strategies and conditions for successful filter regeneration of those systems will be discussed.
54 citations
TL;DR: Mixing of the ππ* transition with high-energy transitions in the peptide backbone and in side chains must be considered to explain the strong negative CD band near 200 nm of PPII.
Abstract: Exciton coupling of the 190 nm ππ* transition is an important factor in the CD spectrum of peptides and proteins. The CD spectrum of the α-helix is dominated by the exciton effect. The spectrum is sensitive to the direction of the ππ* transition dipole moment, especially for short helices. Exciton theory is much less successful in accounting for the CD spectrum of the poly(proline)II (PPII) conformation, an important conformer in collagen and in unordered peptides. Mixing of the ππ* transition with high-energy transitions in the peptide backbone and in side chains must be considered to explain the strong negative CD band near 200 nm of PPII.
51 citations
TL;DR: In this paper, a self-consistent thermodynamic description of the Sn-Ti binary system has been obtained by fitting critically reviewed thermochemical and phase diagram data, and the newest and most consistent lattice stability has been used, and all the intermetallic phases and recent experimental information have been taken into account.
Abstract: The knowledge of phase equilibria and thermodynamic properties in the ternary Cu-Sn-Ti system is of technical importance for active brazing filler metals Thermodynamic descriptions of the binary systems Cu-Ti and Cu-Sn are well established In this work a self-consistent thermodynamic description of the Sn-Ti binary system has been obtained by fitting critically reviewed thermochemical and phase diagram data The newest and most consistent lattice stability has been used, and all the intermetallic phases and recent experimental information have been taken into account The equilibrium measurement on the Sn-rich side and more experimental thermodynamic properties are required for a better thermodynamic description of this system The evaluated thermodynamic description of the Sn-Ti binary system will serve as part of the thermodynamic database for Cu-Sn-Ti brazing alloys
49 citations
TL;DR: In this article, the sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures, and a relatively good agreement is observed.
Abstract: The sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures. For pure metals and Bi–Sn alloys negative temperature coefficients of surface tension have been obtained. In case of Ag–Bi and Ag–Sn alloys the temperature coefficients of surface tension take negative or positive values depending on composition. Experimental values of the surface tension for Ag–Bi, Ag–Sn, and Bi–Sn are compared with those computed from Butler’s model. A relatively good agreement is observed.
48 citations
TL;DR: In this paper, a clean and efficient method for the synthesis of 4H-pyran derivatives through the one-pot condensation of aromatic aldehydes, malononitriles, and β-dicarbonyl compounds, using guanidine base tetramethylguanidine in [bmim][BF4] ionic liquid as a recyclable catalytic system, was described.
Abstract: A clean and efficient method for the synthesis of 4H-pyran derivatives through the one-pot condensation of aromatic aldehydes, malononitriles, and β-dicarbonyl compounds, using guanidine base tetramethylguanidine in [bmim][BF4] ionic liquid as a recyclable catalytic system, was described.
TL;DR: The pico- to nano-level FDCD analysis described in this paper leads to promising opportunities for the stereochemical analysis of a wide range of natural products with minuscule amounts of sample available.
Abstract: In collaboration with Jasco Corporation we have recently developed an FDCD (fluorescence detected circular dichroic) instrument J-465, which eliminates the photoselection artifacts and efficiently collects the emitted light from the sample solution based on the ideal ellipsoidal mirror principle. Using the J-465 we have investigated a variety of fluorophores with/without polarization for exciton-coupled FDCD stereochemical analysis. The following three cases extend the FDCD methodology to new challenging areas beyond the limits of conventional CD: (1) substrates containing C=C double bonds, (2) molecules with sterically hindered hydroxyls, and (3) substrates bearing remote stereogenic centers. The pico- to nano-level FDCD analysis described in this paper leads to promising opportunities for the stereochemical analysis of a wide range of natural products with minuscule amounts of sample available.
TL;DR: The origin of exciton interaction and examples of its application to organic stereochemistry are presented in this paper, where N,N′-Carbonyl-bridged dipyrrinones constitute a new class of highly fluorescent chromophores suitable for investigations of stereochemistry and absolute configuration.
Abstract: (A) The origin of exciton interaction and examples of its application to organic stereochemistry are presented. (B) N,N′-Carbonyl-bridged dipyrrinones constitute a new class of highly fluorescent chromophores suitable for investigations of stereochemistry and absolute configuration. N,N′-Carbonylxanthobilirubic acid esters are strongly fluorescent, with a fluorescence quantum yield (φF) ∼0.8, but produce only weak exciton CD from the trans-1,2-cyclohexanediol template. The ester of an analog with benzoic acid replacing propionic, N,N′-carbonyl-8-(4-carboxyphenyl)-3-ethyl-2,7,9-trimethyl-(10H)-dipyrrin-1-one, exhibits strong fluorescence (φF=0.68, λem=493 nm, λex=422 nm in CHCl3) and UV-Vis absorption (ɛ∼21000 at 424 nm) in organic solvents. Its diester with (1S,2S)-cyclohexanediol is fluorescent and exhibits exciton circular dichroism (Δɛ=+15 dm3·mol−1·cm−1, λ=432 nm; Δɛ=−4 dm3·mol−1 cm−1, λ=380 nm) that correlates with the Exciton Chirality Rule.
TL;DR: A review of recent literature on the formation of supramolecular polymers via hydrogen bonding forces and functional aggregates derived therefrom is presented in this article, with a focus on functional macromolecules.
Abstract: Functional macromolecules can self assemble into regular structures yielding biological structures. The present review assembles recent literature on the formation of supramolecular polymers via hydrogen bonding forces and functional aggregates derived therefrom.
TL;DR: In this article, the structure of the Schiff base NOS donor ligands has been elucidated by elemental analysis, conductance, magnetic susceptibility measurements, IR, ESR, electronic spectral studies and thermal techniques (TGA and DTA).
Abstract: Complexes of Co(II), Ni(II), Cu(II), and Mn(II) containing Schiff base NOS donor ligands have been synthesised via chemical and electrochemical techniques. The structure of the complexes has been elucidated by elemental analysis, conductance, magnetic susceptibility measurements, IR, ESR, electronic spectral studies and thermal techniques (TGA and DTA). The electrochemical behaviour of the metal complexes was studied using DC polarography and cyclic voltammetry. Antimicrobial activity of the title Schiff base and its complexes has been tested against different microorganisms.
TL;DR: In this paper, the impact of loading levels of sulfate ions (3, 6, and 10-wt) on the structural, textural, and surface acid base properties as well as the impacts on catalytic activity towards 2-propanol conversions on γ-Al2O3 and on aluminum hydroxide gel is described.
Abstract: Consequences of the loading level of sulfate ions (3, 6, and 10-wt%) as well as the source of sulfate (H2SO4 or (NH4)2SO4) on the structural, textural, and surface acid–base properties as well as the impacts on catalytic activity towards 2-propanol conversions on γ-Al2O3 and on aluminum hydroxide gel is described. Structural investigations of the catalysts by XRD revealed that the sulfation processes do not remarkably affect the γ-phase of alumina irrespective of the sulfate content or source. N2-adsorption at 77 K indicated that sulfated gel catalysts exhibit the highest S
BET areas and, in general, S
BET for all catalysts were found to decrease with the increase of sulfate content, such a decrease is more pronounced for the 10% loaded catalysts. Pyridine adsorption as followed by FTIR indicated that sulfation of alumina increases the strength of its Lewis acid sites and creates Bronsted acidity in the case of highly loaded catalysts. The catalytic decomposition of 2-propanol in the gas phase indicated that, amongst all the catalysts investigated, the 6% loaded ones exhibited 100% activity (2-propanol conversion) and the highest propene (dehydration product) selectivity.
TL;DR: In this paper, the backbone structure of bis(2-pyridylimino)isoindolate (BPI) ligands was functionalized with several linker units, and the first examples of BPI-platinum complexes were prepared using [(COD)PtCl2] as starting material.
Abstract: With the aim of immobilizing bis(2-pyridylimino)isoindolate (BPI) ligands their backbone structure has been functionalized with several linker units. Their fixation was carried out at the stage of the phthalodinitrile precursor by nucleophilic ipso-substitution of 4-nitrophthalodinitrile. Subsequent synthesis of the functionalized phthalodinitriles with two molar equivalents of the 2-aminopyridine derivatives gave the corresponding BPI ligands. Reaction of the ethyleneglycol functionalized BPI derivative with the zeroth generation carbosilane dendrimer [G-0]4-exo-Cl yielded the functionalized dendrimer [G-0]4-exo-[O(CH2)2O]-10-MeBPI (7). The synthesis of the palladium complexes was carried out by reaction of the protioligands with [(PhCN)2PdCl2] in benzene using triethylamine as auxiliary base whereas the first examples of BPI-platinum complexes were prepared using [(COD)PtCl2] as starting material.
TL;DR: Asymmetric transfer hydrogenation catalysed by chiral ruthenium complexes was the method for enantioselective synthesis of (R)-(+)-coralydine, (S)-(−)-homoprotoberberine, and (S-( +)-homoaporphine in fair to excellent enantiomeric purity.
Abstract: Asymmetric transfer hydrogenation catalysed by chiral ruthenium complexes was the method for enantioselective synthesis of (R)-(+)-coralydine, (S)-(−)-homoprotoberberine, and (S)-(+)-homoaporphine in fair to excellent enantiomeric purity.
TL;DR: In this paper, a retrospective view is given on work carried out at the Johannes Kepler University during the last two decades on the structure formation in crystallizable polymers during their processing, focusing on some useful principles from basic physical chemistry: use of the T,S-diagram and of the temperature dependent courses of surface tensions along coexistence lines of phases.
Abstract: A retrospective view is given on work, which has been carried out at the Johannes Kepler University during the last two decades on the structure formation in crystallizable polymers during their processing. Emphasis is laid on some useful principles lend from basic physical chemistry: use of the T,S-diagram and of the temperature dependent courses of (effective) surface tensions along coexistence lines of phases. These considerations should be helpful in creating an overview, where a deficiency of direct experimental crystallization kinetics data exists. For a series of industrially important, mostly fast crystallizing, polymers data are given in the present paper for the quiescent melt (temperature dependences of number densities of nuclei and of growth speeds). Critical minimum cooling speeds for bypassing crystallization are given on the basis of the given data. These critical cooling speeds vary by almost six decades from HDPE to i-PS. These results are also helpful in the formulation of a viable classification of materials in the light of their processing conditions. This classification includes metals and glass forming minerals as limiting cases for extremely fast and extremely slowly crystallizing materials.
TL;DR: In this article, the electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches, and the calculated dipole moments increase linearly with the square root of the number of monomeric units.
Abstract: The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer.
TL;DR: In this paper, a crossed aldol-condensation reaction of aldehydes and cyclic ketones under microwave irradiation is described, which is simple, efficient, and environmentally benign.
Abstract: A fast alumina-promoted crossed aldol-condensation reaction of aldehydes and cyclic ketones under microwave irradiation is described. This process is simple, efficient, and environmentally benign and proceeds in fairly high yield without any self-condensation.
TL;DR: In this article, the π-electronic system of a given graph G is contained in the characteristic polynomial, PG(x), obtained by expanding the secular determinant of H MO theory.
Abstract: For deciphering the secret of the conventional Huckel ’s (4n + 2)-rule and also for extending it to polycyclic systems the aromaticity index, ΔZ, is introduced based on the graph-theoretical molecular orbital method, which has been developed by the present author. All the information either stabilizing or destabilizing the π-electronic system of a given graph G is contained in the characteristic polynomial, PG(x), obtained by expanding the secular determinant of H MO theory. Instead of this conventional procedure the present author succeeded in obtaining the general expression of PG(x) in terms of the non-adjacent number, p(G, k), for G, defined for the topological index, ZG. By extending this idea ΔZ is defined by taking into account all the contributions not only from the constituting rings but also from the possible combinations of disjoint rings in G. By using ΔZ mathematical origin of the Huckel’s rule was clarified and expanded to the “extended Huckel’s rule” for polycyclic conjugated systems. Applications to bicyclic and polycyclic networks are demonstrated. Discussion on the aromaticity of fullerenes and nanotubes is presented.
TL;DR: This paradigm explains decreased markers of purine catabolism, free radical formation, and muscle tissue disruption after resistance exercise and the increased repair of muscle proteins following long-term L-carnitine supplementation.
Abstract: Early research investigating the effects of L-carnitine supplementation has examined its role in substrate metabolism and in acute exercise performance. These studies have yielded equivocal findings, partially due to difficulties in increasing muscle carnitine concentrations. However, recent studies have proposed that L-carnitine may play a different role in exercise physiology, and preliminary results have been encouraging. Current investigations have theorized that L-carnitine supplementation facilitates exercise recovery. Proposed mechanism is as follows: 1) increased serum carnitine concentration enhances capillary endothelial function; 2) increased blood flow and reduced hypoxia mitigate the cascade of ensuing, destructive chemical events following exercise; 3) thus allowing reduced structural damage of skeletal muscle mediated by more intact receptors in muscle needed for improved protein signaling. This paradigm explains decreased markers of purine catabolism, free radical formation, and muscle tissue disruption after resistance exercise and the increased repair of muscle proteins following long-term L-carnitine supplementation.
TL;DR: In this article, the reactivity of a well defined Rh (I) complex, i.e. Rh(CF3COO)(NHC)(COD) in the hydrosilylation of 1-alkenes, alkynes, and α,β-unsaturated carbonyl compounds, respectively, is described.
Abstract: The reactivity of a well defined Rh (I) complex, i.e. Rh(CF3COO)(NHC)(COD) (1, NHC = 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene, COD = η4-cycloocta-1,5-diene) in the hydrosilylation of 1-alkenes, alkynes, and α,β-unsaturated carbonyl compounds, respectively, is described. With this complex, excellent reactivity was observed and turn-over numbers (TONs) up to 1000 were reached. A supported version of 1 was realized by reaction of RhCl(NHC)(COD) with PS-DVB–CH2–O–CO–CF2–CF2–CF2–COOAg (PS-DVB = poly(styrene-co-divinylbenzene) to yield PS-DVB–CH2–O–CO–CF2–CF2–CF2–COORh(NHC)(COD). This supported version of 1 exhibited at least comparable, in some cases increased reactivity compared to 1 and allowed the rapid removal of the catalyst from the reaction mixture. Due to reduced catalyst bleeding, the synthesis of target compounds with a Rh-content of less than 130 ppm was accomplished.
TL;DR: These newly described functions of carnitine demonstrate that a given metabolite can be involved in a great number of different processes and cell functions.
Abstract: This review gives a brief overview on the importance of L-carnitine for cell function. A well established role of carnitine is the transport of fatty acids (FA) into the mitochondrial matrix. There exist analogous carnitine dependent transport systems for FA into microsomes and peroxisomes. Different membrane transporters control the intracellular homeostasis of carnitine in particular the organic cation transporter OCTN2. Beyond that carnitine is involved in the regulation of gene transcription, inhibits platelet aggregation, stimulates erythropoiesis, acts as a radical scavenger, improves the age-associated decline of learning and memory as well as age associated changes in oxidative metabolism, and inhibits apoptosis of blood cells. These newly described functions of carnitine demonstrate that a given metabolite can be involved in a great number of different processes and cell functions.
TL;DR: In this paper, four polynuclear complexes: [Zn(2picNO)(N3)2]n, [ Zn(4Mepym)N3]n and [Cd(4mepym)(N 3]n]n have been synthesized and characterized by single-crystal X-ray diffraction.
Abstract: Four new polynuclear complexes: [Zn(2picNO)(N3)2]n, [Zn(4Mepym)(N3)2]n, [Cd(2picNO)(N3)2]n, and [Cd(4Mepym)(N3)2]n (2picNO = 2-picoline-N-oxide and 4Mepym = 4-methylpyrimidine) have been synthesized and characterized by single-crystal X-ray diffraction. The structures of the zinc(II) complexes feature five-coordinate zinc atoms, (μ-1,1) azido bridges, monodentate organic ligands, and 1D chains. The cadmium(II) azide complexes contain distorted octahedral metal atoms linked by alternate di-(μ-1,1) and di-(μ-1,3) azido bridges in cis arrangement and these chains are connected by 2picNO bridges giving a honeycomb 2D framework or by 4Mepym bridges forming extended 2D network structure.
TL;DR: In this paper, the ERS and ENDOR spectra of several symmetrical substituted N,N, N, N′,N′, n′-tetraalkyl-p-phenylenediamine radical cations in solution are reported.
Abstract: ESR and ENDOR spectra are reported of several symmetrical substituted N,N,N′,N′-tetraalkyl-p-phenylenediamine radical cations in solution. Different N,N′-alkyl substituted para-phenylenediamines, like the ethyl, n-propyl, and iso-propyl derivative are compared with the parent N,N,N′,N′-tetramethyl-p-phenylenediamine (Wurster’s Blue Cation). N,N,N′,N′-Tetrabenzyl-p-phenylenediamine, 1,4-dipyrrolidinylbenzene, and N,N′-bis[4-(dimethylamino)phenyl]piperazine are additionally investigated. Experimental and calculated hyperfine coupling constants are compared. Characteristic UV-VIS data and redox potentials in acetonitrile are reported, together with the syntheses of the compounds.
TL;DR: In this article, three X-ray crystal structures of tetradentate ligands are described that partially support structural assignments, but also suggest that solid state structures are not always indicative of solution species.
Abstract: Chiral amino alcohols, amino ethers, and amino thioethers were converted to tetradentate ligands by alkylation with a variety of chromophore-bearing alkyl heterocycles. Copper(II) complexes of the ligands display conformational diastereomerism in solution. The resultant propeller-shaped compounds were characterized by a variety of techniques, including exciton coupled circular dichroism (ECCD). Three X-ray crystal structures of complexes are described that partially support structural assignments, but also suggest that solid state structures are not always indicative of solution species. Thus, ECCD may in some cases provide data that is strongly complimentary to X-ray crystallography. These results are presented in a larger context of coordination complexes that display dynamic behavior that can be studied by chiroptical spectroscopy.
TL;DR: In this paper, the (Z)-N-substituted 4-methylene-5-propylidene-2-oxazolidinone dienes were prepared by a one-step synthesis, starting from 2,3-hexanedione and isocyanates.
Abstract: The (Z)-N-substituted 4-methylene-5-propylidene-2-oxazolidinone dienes were prepared by a one-step synthesis, starting from 2,3-hexanedione and isocyanates. Diels-Alder cycloadditions of these dienes were carried out in the presence of the dienophiles methyl vinyl ketone, methyl propiolate, and a captodative olefin, under conditions such as solvents of high polarity, Lewis acid catalysis, and non-conventional energy sources. The reactions carried out either with mixtures of H2O/MeOH or under BF3·Et2O catalysis yielded the highest regio- and stereoselectivities. The use of ionic liquids, microwaves, and ultrasound did not significantly increase the selectivity.
TL;DR: In this paper, a poly(ethylene glycol) was used as the solvent for selective deprotection of 1,1-diacetates (acylals) with easy recyclability of solvent and sodium hydrogen sulfate catalyst.
Abstract: Poly(ethylene glycol) was used as the solvent for selective deprotection of 1,1-diacetates (acylals) with easy recyclability of solvent and sodium hydrogen sulfate catalyst. This method is high yielding, fast, clean, safe, and therefore very suitable for practical organic synthesis.