The catalytic asymmetric synthesis of both α‐substituted and α,α‐disubstituted (quaternary) β‐tetralones through direct α‐functionalization of the corresponding β‐tetralone precursor remains elusive. ...A designed Brønsted base‐squaramide bifunctional catalyst promotes the conjugate addition of either unsubstituted or α‐monosubstituted β‐tetralones to nitroalkenes. Under these reaction conditions, not only enolization, and thus functionalization, occurs at the α‐carbon atom of the β‐tetralone exclusively, but adducts including all‐carbon quaternary centers are also formed in highly diastereo‐ and enantioselective manner.
Kombiniert kontrolliert werden Regio‐, Diastereo‐ und Enantioselektivität bei der direkten α‐Funktionalisierung von β‐Tetralonen durch den Einsatz von Brønsted‐Base(BB)‐Katalyse. Die Lösung dieses alten Problems ebnet den Weg zu dicht funktionalisierten polycyclischen Systemen mit einem vollständig kohlenstoffsubstituierten quartären Stereozentrum.
The base‐catalyzed hydroamination of olefins offers a simple and elegant access to various primary, secondary, and tertiary amines. Particular focus is placed on developments in the area of ...hydroamination of non‐activated olefins. Advantages and disadvantages of the methodology compared to other synthetic methods are presented. Special attention is paid to potential industrial applications of this chemistry.
The influences of acid–base properties of metal oxides on the catalytic performance for synthesis of propylene carbonate from urea and 1,2-propanediol was investigated, and the reaction was stepwise. ...The amphoteric ZnO showed the best activity, and the yield of propylene carbonate reached 98.9%. The urea decomposition over oxides was characterized by using FTIR. ZnO, CaO, MgO and La
2O
3 were favorable to promote urea decomposition to form the isocyanate species, and the formation of isocyanate species was the key to urea alcoholysis. The catalytic activity of urea decomposition was consistency to the catalytic performance for synthesis of propylene carbonate. Based on these, the probable reaction mechanism was proposed.
Während Acylammoniumsalze gut untersucht sind, fanden chirale α,β‐ungesättigte Acylammoniumsalze deutlich weniger Beachtung. Zwar sind diese Intermediate geeignete Synthone, die ausgehend von ...gängigen ungesättigten Säuren und Säurechloriden leicht zugänglich sind und drei reaktive Zentren aufweisen, doch ist ihre Anwendung in der organischen Synthese wegen des Fehlens geeigneter chiraler Lewis‐Basen für ihre Herstellung eingeschränkt. In den vergangenen Jahren wurden neue Einsatzmöglichkeiten für chirale ungesättigte Acylammoniumsalzen entwickelt und somit die einzigartige Reaktivität dieser Intermediate aufgezeigt, was zur Entwicklung eines breitgefächerten Spektrums an katalytischen asymmetrischen Reaktionen, darunter auch Organokaskadenprozesse, führte. Dieser Kurzaufsatz beleuchtet das aktuelle und wachsende Interesse an diesen Intermediaten, das eine weitere Erforschung ihres ungenutzten Potenzials zur asymmetrischen Organokaskaden‐Katalyse auslösen könnte. Ein kursorischer Vergleich wird zu verwandten ungesättigten Iminium‐ und Acylazolium‐Intermediaten gezogen.
Leistungsstark und praxistauglich: In den letzten Jahren stießen chirale ungesättigte Acylammoniumverbindungen als Intermediate wegen der vielfältigen Reaktivität von α,β‐ungesättigten Acylammoniumsalzen und Ammoniumdienolaten zunehmend auf Interesse. Die bequem aus gängigen Säurechloriden oder aktivierten Carbonsäuren und tertiären Aminen als Lewis‐Basen herzustellenden Intermediate führten zu einer Vielzahl an Organokaskadenprozessen.
Es wird über eine Methode zur katalytischen Erzeugung von funktionalisierten Arylalkalimetallverbindungen berichtet. Diese hochreaktiven Intermediate werden aus silylgeschützten, arylsubstituierten ...Diazenen durch Einwirkung von Lewis‐basischen Alkalimetallsilanolaten freigesetzt, wobei Desilylierung und Verlust von N2 eintreten. Katalytische Mengen jener Lewis‐Basen leiten die Übertragung des Arylnukleophils vom Diazen auf Carbonyl‐ und Carboxyverbindungen mit hervorragender Toleranz gegenüber funktionellen Gruppen ein. Die Arylalkalimetallverbindungen können elektrophile Substituenten wie Methoxycarbonyl‐ oder Cyangruppen sowie Halogene tragen. Die Synthese eines bislang nicht bekannten cyclophanartigen 4Arenmakrocyclus ausgehend von einem 1,3‐Bisdiazen in Verbindung mit einem 1,4‐Dialdehyd unterstreicht das Leistungsvermögen des Ansatzes.
Unter Stickstoffschutz: Silylgeschützte arylsubstituierte Diazene wirken als maskierte Arylnukleophile. Ausgelöst durch Me3SiOM (M=Li, Na und K) tritt eine Arylübertragung auf Carbonyl‐ und Carboxygruppen bei Raumtemperatur ein. Diese milde Erzeugung des Nukleophils ist mit elektronenziehenden und ‐schiebenden funktionellen Gruppen (FGs) vereinbar.
Selective hydrogenolysis of glycerol to propylene glycol was performed using an environmentally friendly hydrotalcite-derived mixed-metal oxide catalyst. The Mg/Al, Zn/Al, Ni/Mg/Al, Ni/Co/Mg/Al, and ...Cu/Zn/Al mixed-metal oxide catalysts were prepared from their corresponding hydrotalcite precursors having M2+/M3+ compositions over the range of 0.5−3.0. The physicochemical properties of the catalysts were studied by X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), NH3 and CO2 temperature-programmed desorption (TPD), and nitrogen adsorption studies. The XRD patterns of pure hydrotalcites exhibited characteristics of hydrotalcite phases, while those of calcined hydrotalcites showed the formation of corresponding metal oxides. The ICP-MS analysis showed agreement between the calculated and actual metal compositions. The prepared catalysts were evaluated for the hydrogenolysis of glycerol to propylene glycol in a Parr reactor. The activity studies indicated a maximum glycerol conversion and selectivity toward propylene glycol in the case of Cu/Zn/Al mixed-metal oxide catalysts. Further, the reaction parameters were optimized with the most active Cu/Zn/Al catalyst, and it was found that at a catalyst concentration of 5% (w/w) of aqueous glycerol, a hydrogen pressure of 200 psig, and 80% glycerol dilution, a maximum glycerol conversion of 52% with 93−94% selectivity toward propylene glycol were obtained.
To assess the dynamics of rivers, a reliable characterization of river streamflow during unsteady flow regimes is of paramount importance. In this work, we aimed at investigating the characteristics ...of turbidity–discharge (T–Q) dynamics corresponding to annual artificial dam flush release in a mountainous stream. Two methods for evaluating discharge were used in this study: the classical rating curve and the fluvial acoustic tomography (FAT) system that was developed by Hiroshima University. Interestingly, during dam flush, the discharge records obtained by FAT showed striking features of unsteady streamflow behavior, such as discharge shoulders and, in some events, secondary discharge peaks. According to the T–Q hysteresis loops, the common type of T–Q observed patterns were anticlockwise loops. During the studied DF events, sediment was supplied by river banks located at different sites along the river channel.
•Short-scale streamflow variations during dam flush events were monitored by a novel acoustic tomography system.•Distinctive features were observed in the discharge hydrographs, which differed from the original flush patterns.•Turbidity–discharge hysteresis due to artificial dam flush was studied.
A method for the synthesis of 1,1‐diborylalkenes through a Brønsted base catalyzed reaction between terminal alkynes and bis(pinacolato)diboron has been developed. The procedure allows direct ...synthesis of functionalized 1,1‐diborylalkenes from various terminal alkynes including propiolates, propiolamides, and 2‐ethynylazoles.
Alkinfunktionalisierung: Eine Brønsted‐Base‐katalysierte Reaktion zwischen Bis(pinakolato)dibor und verschiedenen terminalen Alkinen, einschließlich Propiolaten, Propiolamiden und 2‐Ethinylazolen, ermöglicht die direkte Synthese von funktionalisierten 1,1‐Diborylalkenen.
High concentration of fluorine (F) in agricultural soils has got significant attention considering its impacts on human health, but little information was available about F distribution in farmland ...soil profiles around phosphorous chemical industry factories. In present study, farmland soil profiles and relevant medium samples were collected from farmlands around a main phosphorous chemical base in southwest China. At 0–100-cm profiles, concentrations of soil total F (Ft, 400.9–1612.0 mg kg
−1
) and water soluble F (Fw, 3.4–26.0 mg kg
−1
) decreased with profile depth in industrial areas. Industrial activities enhanced F concentration in soil mainly at 0–40-cm profiles. No disparity for both Ft and Fw distributions in paddy-dry land rotation field and dry land indicates short-term land utilization could not affect the F distribution in soil profiles. Correlation analysis showed soil organic matter and wind direction were important factors influencing the distribution of F in soil profiles. The shutdown of factory and government control of industrial emissions effectively decreased the ambient air F (Fa) concentrations in industrial areas. In where Fa and dustfall F concentrations were high, high soil Ft, Fw, and crop edible part F concentrations were found.
An easy-to-implement solid/liquid extraction method has been developed to extract the basic molecules from petroleum crude oil in significant amounts (700−800 mg). The basic molecules are first ...extracted from crude oil using a cation-exchange sorbent, then recovered using methylamine. After checking the quantitativity of the method with model systems composed of commercially available basic and nonbasic molecules, four different crude oils spanning different properties (from light oil to extra-heavy crude oils) were tested. The efficiency of the method has been checked by determining the extraction yield from elemental analysis and titration measurements (total base number determination). Results show that 80−90% of bases are extracted from crude oils having densities comprised between 0.875 and 0.939 g.cm−3 at 15 °C. The extraction yield is significantly lower for an extra-heavy crude oil (around 70%).
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