Showing papers in "Journal Fur Praktische Chemie-chemiker-zeitung in 2000"
TL;DR: In this article, the preparation and the synthetic utility of Weinreb amides for the preparation of aldehydes and ketones has been discussed, and various reagents based on Weinreb′s amide have been compiled.
Abstract: The preparation and the synthetic utility of the N-methoxy-N-methyl amides, also called as Weinreb amides, for the preparation of aldehydes and ketones has been discussed. Also the various reagents based on Weinreb′s amide has been compiled.
127 citations
TL;DR: In this paper, the utility of high pressure for the understanding of chemical reactions and its application in organic synthesis is shown for cycloadditions, cheletropic reactions and pericyclic rearrangements.
Abstract: The utility of high pressure for the understanding of chemical reactions and its application in organic synthesis is shown for cycloadditions (inter- and intramolecular Diels-Alder reactions, 1,3-dipolar and [2+2] cycloadditions), cheletropic reactions and pericyclic rearrangements (Cope and Claisen rearrangements and electrocyclizations). The origin of the effect of pressure on chemical reactions is discussed. Especially, the change in the packing coefficient during cyclization of chains and the effect of electrostriction on reactions, in which charged species are generated, contribute substantially to a volume contraction leading to a powerful pressure-induced acceleration of such reactions. Finally, the effect of pressure on free-radical reactions (homolytic bond dissociations and quinone oxidations) is described.
69 citations
TL;DR: Recent sol-gel techniques enable bioactive composite layers to be prepared by the embedding of bioactive compounds, biomolecules and cellular systems within inorganic layers that offer interesting new applications, e.g. biocompatible coatings on implants and medical products, and coatings that can release biocides in a controlled manner.
Abstract: Recent sol-gel techniques enable bioactive composite layers to be prepared by the embedding of bioactive compounds, biomolecules (BMs) and cellular systems within inorganic layers. These novel bioactive layers offer interesting new applications, e.g. biocompatible coatings on implants and medical products, the preparation of biosensors and biocatalysts, and coatings that can release biocides in a controlled manner.
61 citations
TL;DR: In this article, a new intramolecular solid-state thermal condensation is reported, where Enaminoketones are synthesized quantitatively from anilines and 1,3-diketones without catalysis and those can be used for quantitative solid state 4cascade reactions.
Abstract: Numerous reaction types in the field of iminium salts are performed in the gas-solid and solid-solid techniques in order to reach 100% yield. The stoichiometric runs are waste-free and do not require costly workup. Frequently, iminium salts were avoided, as acid catalysis was dispensable. Thioureas and α-halogenated ketones give a variety of 2-aminothiazoles via thiuronium salts in quantitative yield. A new intramolecular solid-state thermal condensation is reported. Enaminoketones are synthesized quantitatively from anilines and 1,3-diketones without catalysis and those can be used for quantitative solid-state 4-cascade reactions. Solid paraformaldehyde is used to produce methylene imines and internally trapped methylene iminium salts. Benzoylhydrazones are produced again without catalysis in the solid state. Vacuum and ball-mill techniques are particularly useful in the production of highly sensitive iminium salts. Hexahydro-1,3,5-triazines cyclorevert upon exposure to HCl gas to give solid arylmethylene iminium chlorides as new versatile reagents. These are used in arylaminomethylations of β-naphthol and of themselves to give Troeger's bases in 3-cascades. More direct are 4-cascade Troeger's base syntheses by dissolving hexahydro-1,3,5-triaryltriazines in trifluoroacetic acid. Alkylations of imines with trimethyloxonium tetrafluoroborate and triphenylmethyl cation give highly sensitive quaternary iminium salts in the ball-mill. The products are characterized by spectroscopic techniques and density functional theory (DFT) calculations at the B3LYP 6-31G* level. Molecular movements in the crystal and surface passivation are investigated with atomic force microscopy (AFM) techniques.
53 citations
TL;DR: In this paper, the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate (bmim PF6) has been studied as a catalyst medium for biphasic homogeneous hydrogenations of sorbic acid.
Abstract: The ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate (bmim PF6) (6) has been studied as catalyst medium for biphasic homogeneous hydrogenations of sorbic acid (1). As catalyst we used the Cp*-ruthenium-complex [Cp*Ru(η4-CH3—CHCH—CHCH—COOH) (CF3SO3)] which efficiently enables the stereoselective hydrogenation of sorbic acid leading to the formation of cis-3-hexenoic acid (3) in selectivities of up to 90% with turnover frequencies of up to 1100 h—1. Compared to other biphasic systems the hydrogenation in bmim PF6 proceeds with enhanced activity. The kinetics can be described with a Michaelis Menten-equation, and the activation energy for the whole process was determined to be EA = 78 ± 5 kJ/mol.
52 citations
36 citations
TL;DR: A systematic nomenclature for mechanically linked molecules such as catenanes, rotaxanes, and assemblies derived from these structural elements was introduced in this paper.This nomencature is based on the increasing complexity of already synthesized interlocked molecules and the ones to be expected in future.
Abstract: We introduce a systematic nomenclature for mechanically linked molecules such as catenanes, rotaxanes, and assemblies derived from these structural elements which comes up to the increasing complexity of already synthesized interlocked molecules and the ones to be expected in future Like in the naming of other substance classes (polycycles, phanes, crown compounds, podands, dendrimers) we attach importance to the fact, that certain units in the name, eg expressions in brackets, quickly convey an idea of the molecular architecture Furthermore, this modular nomenclature reveals as many analogies to the IUPAC nomenclature as possible
33 citations
TL;DR: The allenyl p-methoxybenzyl ketone 3a and p-siloxyphenyl ketones 6b selectively delivered three different products with three different transition metal-catalysts.
Abstract: The allenyl p-methoxybenzyl ketone 3a and allenyl p-siloxybenzyl ketones 6b selectively delivered three different products with three different transition metal-catalysts. With Hg(II)-catalysts a spiro[4.5]decene 9, with Ag(I)-catalysts a 2-substituted furan (10/11) and with Pd(II)-catalysts a 2,4-disubstituted furan (8/12) was formed. Only with perchloric acid the intermolecular addition of water to the allene, leading to 1,3-dicarbonyl compounds 7, was observed. While with the corresponding allenyl o-methoxybenzyl ketone 3b the Ag(I)- and Pd(II)-catalysts provided the expected products, the mercury-catalyst led to a new and interesting side-product rac-17 which combined both the furan moiety and the spiro[4.5]decene moiety. Efforts to prepare allenyl hydroxybenzyl ketones failed, in one case a small amount of a 5H-benzo[b]oxepin-4-one 21 was isolated. It also was not possible to extend the spirocyclization to allenyl p-siloxyphenyl ketone 6a or allenyl 2-(p-siloxyphenyl)ethyl ketone 6c.
32 citations
TL;DR: In this article, Carboxylic acids were converted into the corresponding acid fluorides 4a-g using cyanuric fluoride using a simple preparation procedure, cheap reactants and a low time exposure.
Abstract: Cyanuric fluoride (2) is one of the most popular fluorinating agents in organic chemistry. The title compound could be prepared in a 50 to 100 g scale by means of a chlorine fluorine exchange, the process was characterized by a simple preparation procedure, cheap reactants and a low time exposure. Carboxylic acids were converted into the corresponding acid fluorides 4a-g using cyanuric fluoride. A non-aqueous work-up led to high yields on synthesizing a range of functionalized acid fluorides.
30 citations
29 citations
TL;DR: In this article, the authors focus on Diels-Alder reactions of 2 and the applications of norbornene derivatives in organic synthesis and propose a rigid framework that act as a powerful template to provide high degree of selectivity and directional nature to various substituents.
Abstract: Readily available 1,2,3,4-tetrachloro-5,5-dimethoxy- cyclopenta-1,3-diene (2) is an excellent cyclic diene for Diels-Alder reaction with a vast variety of dienophiles. The products so formed (norbornene derivatives) constitute important building blocks for the synthesis of diverse complex natural as well as non-natural products. Apart from very high endo selectivity associated with Diels-Alder reactions, there are several other fascinating features associated with these bicyclic products which make them convenient entities in the synthesis of complex molecules. The most important is the rigid framework that act as a powerful template to provide high degree of selectivity and directional nature to various substituents. The proposed article is intended to focus on Diels-Alder reactions of 2 and the applications of norbornene derivatives in organic synthesis.
TL;DR: AzaPcs 3-5 give green pyridine solutions with Q-bands at 650-670 nm and e-values of 60 000-190 000 as discussed by the authors, in good yields from condensations of diaminomaleonitrile and the diketones 2, 2′-furil, 2,2′-thenil and 2,
Abstract: Magnesium, copper(II) and nickel(II) complexes of octasubstituted azaphthalocyanines 3 — 5 have been prepared from di-fur-2-yl, di-thien-2-yl and di-pyrid-2-yl pyrazine-2,3-dicarbonitriles 2. Compounds 2 were prepared in good yields from condensations of diaminomaleonitrile and the diketones 2,2′-furil, 2,2′-thenil and 2,2′-pyridil. AzaPcs 3—5 give green pyridine solutions with Q-bands at 650—670 nm and e-values of 60 000—190 000.
TL;DR: In the last two years, several new protocols for the Suzuki coupling with aryl chlorides have been developed as mentioned in this paper, which allow an efficient synthesis of biaryls of type 1, independently of the substitution pattern and electronic properties of the starting materials.
Abstract: The Suzuki coupling represents a widely used method for the synthesis of biarylic compounds 1 and has been already applied on industrial scale. Unfortunately, for a long time this reaction was limited to the use of aryl bromides, aryl iodes or electron-deficient aryl chlorides as starting materials. Thus, a general approach to the desired biarylic compounds 1 using the cheap and easy available aryl chlorides has not been available. In the last two years, however, several new protocols for the Suzuki coupling with aryl chlorides have been developed. These methods allow an efficient synthesis of biaryls of type 1, independently of the substitution pattern and electronic properties of the starting materials. These concepts which have been developed by the research groups of Fu, Buchwald, Guram, Beller as well as Trudell and Nolan are highlighted in this review.
TL;DR: In this article, the authors investigated solvent-free oxidations of organic model compounds with potassium permanganate on inorganic carriers and concluded that mechanochemical stimulation can induce oxidations.
Abstract: Mechanochemical Oxidation of Organic Model Compounds by Means of Potassium Permanganate
Systematical investigation of solvent-free oxidations of organic model compounds with potassium permanganate on inorganic carriers leads to conclusion, that mechanochemical stimulation can induce oxidations. In case of the benzyl-type arenes these conversions are selective at good yields. Olefines react to carbonic acids. The presence of water enhances the yield of almost all educts.
TL;DR: The N-Vinylformamide (VFA) is the simplest member of the enamide group and is the key compound in the synthesis of linear cationic polymers with primary amino groups as discussed by the authors.
Abstract: N-Vinylformamide (VFA), the simplest member of the enamide group, is the key compound in the synthesis of linear cationic polymers with primary amino groups. In recent decades VFA has been the object of intensive research activity in industry and in universities with the aim of developing an economic method of synthesis. The various principles underlying the synthesis are described and the possibilities for their industrial realisation are discussed. From the large number of methods two variants have now been established as industrial production procedures at BASF and Mitsubishi Kasei Corp. (MKC). VFA is now available in tonne quantities in high purity. An overview of the versatile reaction possibilities of this multifunctional monomer and an extensive list of references are also given. The radical polymerisation to polyvinylformamides and their further reaction to polyvinylamines are not covered in this review.
TL;DR: In this paper, the reaction of BuSeLi, made from BuLi and elemental selenium, with chlorosilanes MexPhySiCl4-x-y led to selenobutyl substituted derivatives.
Abstract: The reaction of BuSeLi, made from BuLi and elemental selenium, with chlorosilanes MexPhySiCl4-x-y led to selenobutyl substituted derivatives. In the cases of polychlorosilanes formation of the completely substituted products MexPhySi(SeBu)4-x-y are favoured. Higher yields of partially substituted products could be obtained by reaction of chlorosilanes with BuSeH/NEt3. Besides monosilanes the reactions of several methylchlorodi-, tri- and isotetrasilanes with BuSeLi and BuSeH/NEt3 were also investigated. In SiClMe(SiClMe2)2 the chlorine substituent at the middle silicon atom is substituted by BuSeH/NEt3 at first selectively. All products were characterized by 1H, 13C, 29Si and 77Se NMR and trends of chemical shifts and coupling constants (1JSiSi, 1JSiSe, 2JSiSe) with the substitution pattern were investigated.
TL;DR: Feeding experiments shed light on the biosynthetic origin of the chromophore, the N-acetyl groups, the 4-C-methyl group of the moenuronamide unit, the sugar units, and the lipid part of the antibiotic moenomycin A(1).
Abstract: Feeding experiments ( 13C and 15N-labeled precursors) shed light on the biosynthetic origin of the chromophore (unit A of 1), the N-acetyl groups, the 4-C-methyl group of the moenuronamide unit (part F of 1), the sugar units, and the lipid part (unit I of 1) of the antibiotic moenomycin A(1). The lipid part is completely isoprenoid and is constructed via the non-mevalonate pathway. The central C 10 part originates from a precursor like geranyl or linalyl diphosphate and is formed by a route involving ring formation between C-2 and C-6 of the monoterpene unit, two successive rearrangements to give a 7-membered ring intermediate and cleavage of the ring between C-5 and C-11 (moenocinol numbering).
TL;DR: In this paper, the reaction of benzenediazonium chloride with active [1, 2, 4]triazin-3-ylthio-methylene compounds has been studied.
Abstract: Reaction of benzenediazonium chloride with active [1,2,4]triazin-3-ylthio-methylene compounds 3 afforded the azo coupling products 5, which yielded [1,2,4]triazolo[4,3-b][1,2,4]triazin-7(1H)-ones 8 upon treatment with sodium ethoxide in ethanol. The latter products 8 were characterized on the basis of alternate synthesis and spectral data. The mechanism of formation of 8 and the regiochemistry of the studied reactions are discussed.
TL;DR: In this article, it was shown how to transform the azavinylogous formamidinium salt with piperidine or morpholine in the presence of trime-thylborate to give the ortho formic acid amide.
Abstract: The formamidinium salts 11a, c as well as the nitrile 12 react with sodiumhydride/dimethylamine in the presence of trimethylborate to give the ortho formic acid amide 3a. The orthoamides 6a and 16 can be prepared from the iminium salts 15 and 14, resp. by the same procedure. Treatment of the azavinylogous formamidinium salt 15 with sodiumhydride and piperidine or morpholine in the presence of trime-thylborate affords the orthoamides 6c and 6d, resp. By transamination of the azavinylogous aminalester 5a are accessible the orthoamides 6b—d. The vinylogous orthocarbonic acid derivative 17 can be obtained from the salt 14 and sodium alcoholates. The action of sodiumhydride, dimethylamine and trimethylborate on the iminium salt 18 produces a mixture of the orthocarbonic acid derivatives 7a, 8a, 9a. When the guanidinium salt 20 is treated with the same reagents the ortho-amides 3a and 10a are obtained. The reduction of the salt 20 with sodiumhydride in the presence of several activating reagents (e.g. tetrabutyl orthotitanate, aluminiumisopropylate, trimethylborate) affords the orthoamide 3a. The reduction of the iminium salts 18 and 24 does not proceed clean, giving mixtures of various orthoformic acid derivatives. The form-amidine 25 can be prepared by reduction of the salt 15 with sodiumhydride/trimethylborate with good yields. By the action of the corresponding carbanions on the guanidinium salt 20 can be obtained the carboxylic acid orthoamides 26—33. By the same procedure the orthoamides of alkyne carboxylic acids 36a—h, j—n are accessible.
TL;DR: In this paper, two alternative pathways from 2-fluoro aldehydes 5a-d, either by Horner-Wadsworth-Emmons reaction or by Wittig reaction, were presented.
Abstract: γ-Fluoro-α, β-unsaturated carboxylic esters 7a, 7b and 7d and 4-fluoro-4-phenylbut-3-enoic ester (8) are obtained by two alternative pathways from 2-fluoro aldehydes 5a—d, either by Horner—Wadsworth—Emmons reaction or by Wittig reaction. The aldehydes 5a—d are prepared by Swern oxidation of the corresponding fluorohydrins 4a—d. These are available from α-olefins by bromofluorination, bromineby-acetate replacement and subsequent hydrolysis.
TL;DR: In this paper, the influence of substitution on the absorption and luminescence spectra of oligo(phenylenevinylene)s has been studied using distyrylbenzene (DSB) as a model compound.
Abstract: The influence of substitution on the absorption and Luminescence spectra of oligo(phenylenevinylene)s has been studied using distyrylbenzene (DSB) as a model compound. The degree, character, and pattern of substitution was varied systematically, altering the electronic properties of the DSB, the wavelength of the emitted light could be tuned over a range of 100 nm. The syntheses of 6b—h were performed by twofold Wittig Horner-olefinations of bisphoshonates 1a, b with substituted benzaldehydes 2a—i, 6ivia Heck-reaction of the dibromosulfonylbenzene 3, 6k by Siegrist-reaction of 4 with N-phenylbenzaldimine and the Knoevenagel-reaction of benzyl cyanide with 5 led to 6l.
TL;DR: The title compounds were synthesized by 1,3dipolar cycloaddition of 3,3,3-trifluoropropropinyl benzene to azido sugars as mentioned in this paper.
Abstract: The title compounds were synthesized by 1,3-dipolar cycloaddition of 3,3,3-trifluoropropinyl benzene (2) to the azido sugars 2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl azide (1), 6-O-acetyl-4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranosyl azide (6), 6-azido-6-deoxy-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (12), and methyl 6-azido-4-O-cyclohexylcarbamoyl-6-deoxy-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (16), respectively. Because of the dissymmetry of the dipolarophile 2, always two regioisomeric products were obtained, the nucleoside-analogous compounds 3/4 (from 1) and 7/8 (from 6), respectively, and the reversed nucleosides 13/14 (from 12) and 17/18 (from 16), respectively. Protecting group chemistry like transesterification, deacetalation, hydrodechlorination is demonstrated in some cases. Thus, the trichloroethylidene derivatives 7, 8, 17, and 18 were converted into the corresponding ethylidene derivatives (9, 10, 19, 20) by treatment with tributylstannane/AIBN. An X-ray analysis is given for the 1-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-4-trifluoromethyl-5-phenyl-1,2,3-triazole (4) and for the 1-[6-O-acetyl-4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranosyl]-4-trifluoromethyl-5-phenyl-1,2,3-triazole (7).
TL;DR: By coupling of aryldiazonium salts 5 with N,N-disubstituted 2-amino-5H-selenazoles 4 deeply coloured 5-arylazo-substitized 2-AMino-selENazoles 6a-6l have been prepared and their solvatochromic properties determined by means of UV/Vis spectroscopy as mentioned in this paper.
Abstract: By coupling of aryldiazonium salts 5 with N,N-disubstituted 2-amino-5H-selenazoles 4 deeply coloured 5-arylazo-substituted 2-amino-selenazoles 6a—6l have been prepared and their solvatochromic properties determined by means of UV/Vis spectroscopy, and compared with the ones of several other arylazosubstituted N,N-dialkylanilines 7a—7d, 2-(N,N-dialkylamino)-thiophenes 8a—8e, and 2-(N,N-dialkylamino)-thiazoles 9a—9c.