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Research Area B
Publications 2014

Sunlight is the ultimate driver of biosynthesis but photochemical steps late in biosynthetic pathways are very rare. They appear to play a role in the formation of certain furanocembranoids isolated from Caribbean corals. One of these compounds, ​intricarene, has been suspected to arise from an intramolecular 1,3-dipolar cycloaddition involving an oxidopyrylium. ... READ MORE

Second-order rate constants for the reactions of acceptor-substituted phenacyl (PhCO[BOND]CH−[BOND]Acc) and benzyl anions (Ph[BOND]CH−[BOND]Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of ... READ MORE

Electrophoresis is a very important tool in chemistry, biochemistry, and biology and is commonly used for the separation and analysis of molecules. Typically, electrophoresis is performed at the macroscopic level. With a view on integrating molecular separations into micro- and nanofluidic and massively parallel systems, it would be highly desirable to obtain ... READ MORE

X-ray structures of enamines and iminium ions derived from 2-tritylpyrrolidine (Maruoka catalyst) and 2-(triphenylsilyl)pyrrolidine (Bolm–Christmann–Strohmann catalyst) have been determined. Kinetic investigations showed that enamines derived from phenylacetaldehyde and pyrrolidine (R = H) or 2-(triphenylsilyl)pyrrolidine (R = SiPh₃) have similar reactivities ... READ MORE

The kinetics of the hydride abstractions by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) from 13 C–H hydride donors (acyclic 1,4-dienes, cyclohexa-1,4-dienes, dihydropyridines), tributylstannane, triphenylstannane, and five borane complexes (amine–boranes, carbene–boranes) have been studied photometrically in dichloromethane solution at 20 °C. Analysis of the ... READ MORE

Broadly tunable picosecond pulses in the UV for nonlinear microscopy and lifetime measurements are not yet readily available. Complex synchronously pumped optical parametric oscillators with subsequent frequency doubling are typically used. We show that direct second harmonic generation of a visible picosecond supercontinuum source at 78 MHz renders pulses easily ... READ MORE

A short total synthesis of the published structure of racemic trichodermatide A is reported. Our synthesis involves a Knoevenagel condensation/Michael addition sequence, followed by the formation of tricyclic hexahydroxanthene-dione and a diastereoselective bis-hydroxylation. The final product, the structure of which was confirmed by X-ray crystallography, has NMR ... READ MORE

The kinetics of the reactions of carbocations with carbanions 1 derived from 5-benzyl-substituted Meldrum’s acids 1-H (Meldrum’s acid=2,2-dimethyl-1,3-dioxane-4,6-dione) were investigated by UV/Vis spectroscopic methods. Benzhydryl cations Ar2CH+ added exclusively to C-5 of the Meldrum’s acid moiety. As the second-order rate constants (kC) of these reactions in ... READ MORE

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Kinetics and mechanisms of the reactions of p-quinone, 2,5-dichloro-p-quinone, 2,3,4,5-tetrachloro-p-quinone (chloranil), 2,3,4,5-tetrafluoro-p-quinone (fluoranil), and 3,4,5,6-tetrachloro-o-quinone with π-nucleophiles (siloxyalkenes, enamines) and amines have been investigated. Products arising from nucleophilic attack at all conceivable sites, that is, at C and ... READ MORE

The addition of TMPLi to a mixture of an aromatic or heteroaromatic substrate with a metal salt such as MgCl2, ZnCl2, or CuCN at −78 °C first leads to lithiation of the arene followed by transmetalation with the metal salt to afford functionalized organometallic compounds of Mg, Zn, or Cu. This in situ trapping method allows an expedited metalation ... READ MORE

Newly generated frequencies during bulk continuum generation with femtosecond pump pulses do not fluctuate statistically and show strong correlations in spectrum and time. When a femtosecond continuum is used as probe light for transient spectroscopic measurements, these correlations result in a seemingly low noise level but large-scale pseudo-structures that obscure ... READ MORE

A series of α,β-unsaturated iminium ions derived from substituted cinnamaldehydes and C2- and C5-substituted chiral imidazolidin-4-ones were isolated and characterized in solution and in the solid state. The kinetics of the reactions of the iminium ions with silyl ketene acetals were determined in dichloromethane at 20 °C. The resulting second-order rate ... READ MORE

Reaktionen von Donor-substituierten Diarylcarbeniumionen Ar2CH+ mit Inamiden liefern 1-Amid-substituierte Allylkationen (α,β-ungesättigte Iminiumionen). Kinetische Studien zeigen, dass diese Additionsprodukte einer C-H-Bindung an eine CC-Dreifachbindung stufenweise gebildet werden, wobei zunächst Keteniminiumionen entstehen, die anschließend eine ... READ MORE

The kinetics of the reactions of maleic anhydride, N-methylmaleimide, fumaronitrile, diethyl fumarate, and diethyl maleate with pyridinium and sulfonium ylides were studied in DMSO at 20 °C. All of the reactions were found to follow a second-order rate law, and can be described by the linear free energy relationship log k2 (20 °C) = sN(N + E), where N and sN are ... READ MORE

Nanosized mesoporous silica particles with high colloidal stability attract growing attention as drug delivery systems for targeted cancer treatment and as bioimaging devices. This Perspective describes recent breakthroughs in mesoporous silica nanoparticle design to demonstrate their high potential as multifunctional drug delivery nanocarriers. These types of ... READ MORE

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