Synthesen von Heterocyclen, 114. Mitt.: Über Reaktionen von Isatosäureanhydrid mit Isothioharnstoffen,Carbodiimiden und Cyanamiden

Zusammenfassung S-Äthyl-N,N-disubst. bzw.-Arylmonosubst. Isothioharnstoffe reagieren mit Isatosäureanhydrid (1) über die jeweiligen N-Acylderivate zu Abkömmlingen des Chinazolinons. Auch Carbodiimide und Cyanamide können mit1 umgesetzt werden, wobei die gleichen Endprodukte in merklich geringeren Ausbeuten anfallen. Aus dieser Tatsache wird auf den Reaktionsmechanismus geschlossen.

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S-Ethyl-N,N-disubstituted or N-aryl-monosubstituted isothioureas react with isatoic anhydride (1) via the corresponding N-acyl compounds yielding derivatives of quinazoline. Carbodiimides and cyanamides react with1 giving the same compounds in much lower yield. The mechanism of these reactions is discussed in detail.

     

Synthesen von heterocyclen, 129. Mitt.: Ein Beitrag zum Indolonproblem

Zusammenfassung o-Methylamino-phenylglyoxal-dimethylacetal (9), welches aus 4-Hydroxy-1-methyl-carbostyril in dreistufiger Reaktionsfolge zugänglich ist, gibt bei saurer Hydrolyse N,N-Dimethylindigotin (10). Die Bildungsweise von10 wird im Hinblick auf das Indolonproblem diskutiert.

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Syntheses of heterocycles, CXXIX: A contribution to the indolon question

o-Methylamino-phenylglyoxal dimethyl acetal9, obtained by a three step synthesis starting with 4-hydroxy-1-methyl-2-quinolone, gives N,N-dimethyl-indigo10, if hydrolyzed under acid catalysis. The formation of10 is discussed in view of the indolon problem.

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Herrn Prof. Dr.Marius Rebek zum 80. Geburtstag gewidmet.     

Synthesen von Heterocyclen, 125. Mitt.: Über kondensierte Chinoxalinderivate

Zusammenfassung Die Reaktion einiger Mesoxalylheterocyclen sowie deren Aminale mit o-Phenylendiamin wird beschrieben. Die entstehenden kondensierten Chinoxaline können, wenn auch in schlechterer Ausbeute, aus den entsprechenden Dichlormalonylheterocyclen erhalten werden.

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Syntheses of heterocycles, CXXV.: Condensed derivatives of quinoxaline

The reaction of some mesoxalyl derived heterocyclic compounds and their aminals with o-phenylenediamine is described. The condensed quinoxaline derivatives obtained are also formed by the reaction of the corresponding dichloromalonyl heterocycles with o-phenylenediamine, though in much lower yield.

     

Mechanistic insights on azide-nitrile cycloadditions: on the dialkyltin oxide-trimethylsilyl azide route and a new Vilsmeier-Haack-type organocatalyst

The mechanism of the azide-nitrile cycloaddition mediated by the known dialkylltin oxide-trimethylsilyl azide catalyst system has been addressed through DFT calculations. The catalytic cycle for this tin/silicon complex-based mechanism has been thoroughly examined, disclosing the most plausible intermediates and the energetics involved in the rate enhancement. In addition, a new catalyst, 5-azido-1-methyl-3,4-dihydro-2H-pyrrolium azide, is presented for the formation of tetrazoles by cycloaddition of sodium azide with organic nitriles under neutral conditions. The efficiency of this organocatalyst, generated in situ from N-methyl-2-pyrrolidone (NMP), sodium azide, and trimethylsilyl chloride under reaction conditions, has been examined by preparation of a series of 5-substituted-1H-tetrazoles. The desired target structures were obtained in high yields within 15-25 min employing controlled microwave heating. An in depth computational analysis of the proposed catalytic cycle has also been addressed to understand the nature of the rate acceleration. The computed energy barriers have been compared to the dialkylltin oxide-trimethylsilyl azide metal-based catalyst system. Both the tin/silicon species and the new organocatalyst accelerate the azide-nitrile coupling by activating the nitrile substrate. As compared to the dialkylltin oxide-trimethylsilyl azide method, the organocatalytic system presented herein has the advantage of higher reactivity, in situ generation from inexpensive materials, and low toxicity.     

Rapid nickel-catalyzed Suzuki-Miyaura cross-couplings of aryl carbamates and sulfamates utilizing microwave heating

High-speed and scalable nickel-catalyzed cross-coupling of arylboronic acids with aryl carbamates and sulfamates is achieved by using sealed-vessel microwave processing.     

Continuous‐flow syntheses of heterocycles

This review surveys the synthesis of heterocycles under continuous‐flow conditions, including the use of chip‐based microreactors, coil‐based flow reactors, and capillary or tubular devices. J. Heterocyclic Chem., 2011.     

A critical assessment of the specific role of microwave irradiation in the synthesis of ZnO micro- and nanostructured materials

A rapid, microwave-assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3-4 μm in length and 200-300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single-mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol-gel process at 200 °C from a Zn(acac)(2) (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.     

An evaluation of microwave-assisted derivatization procedures using hyphenated mass spectrometric techniques

The potential of microwave-assisted derivatization techniques in systematic toxicological analysis using gas chromatography coupled with mass spectrometry (GC–MS) was evaluated. Special emphasis was placed on the use of dedicated microwave reactors incorporating online temperature and pressure control. The use of such equipment allowed a detailed analysis of several microwave-assisted derivatization protocols comparing the efficiency of microwave and conventional heating methods utilizing a combination of GC–MS and liquid chromatography coupled with mass detection (LC–MS and LC–MS/MS) techniques. These studies revealed that for standard derivatization protocols such as acetylation (exemplified for codeine and morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) a reaction time of 5 min at 100 °C in a microwave reactor was sufficient to allow for an effective derivatization. Control experiments using standard operating procedures (30 min at 60 °C conventional heating) indicated that the faster derivatization under microwave irradiation is a consequence of the higher reaction temperatures that can rapidly be attained in a sealed vessel and the more efficient heat transfer to the reaction mixture applying direct in core microwave dielectric heating. The results suggest that microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

Ylide von Heterocyclen,VIII Reaktionen von Iodonium-Yliden mit Säuren

The reaction of various organic and inorganic acids (HX) with iodonium ylides2 leads to nucleophilic substitution of the iodobenzene substituent by the anionX ^– to yield the heterocycles5. Some of them are hydrolyzed to the hydroxy compounds3 or reduced to the starting compounds1 under the reaction conditions. Reaction of the iodonium ylide2b with monomethyl sulfate gives the salt9, which with bases undergoes nucleophilic substitution to compounds8 and10–12, respectively, or is converted to2b again.