A conforming auxiliary space preconditioner for the mass conserving stress-yielding method

We are studying the efficient solution of the system of linear equations stemming from the mass conserving stress-yielding (MCS) discretization of the Stokes equations. We perform static condensation to arrive at a system for the pressure and velocity unknowns. An auxiliary space preconditioner for the positive definite velocity block makes use of efficient and scalable solvers for conforming Finite Element spaces of low order and is analyzed with emphasis placed on robustness in the polynomial degree of the discretization. Numerical experiments demonstrate the potential of this approach and the efficiency of the implementation.     

Comprehensive Study of the Enhanced Reactivity of Turbo-Grignard Reagents**

Since its introduction in 2004, Knochel's so called Turbo-Grignard reagents revolutionized the usage of Grignard reagents. Through the simple addition of LiCl to a magnesium alkyl an outstanding increase in reactivity can be achieved. Though the exact composition of the reactive species remained mysterious, the reactive mixture itself is readily used not only in synthesis but also found its way into more distant fields like material science. To unravel this mystery, we combined single-crystal X-ray diffraction with in-solution NMR-spectroscopy and closed our investigations with quantum chemical calculations. Using such a variety of methods, we have gained insight into and an explanation for the extraordinary reactivity of this extremely convenient reagent by determining the structure of the first bimetallic reactive species [t-Bu₂Mg ⋅ LiCl ⋅ 4 thf] with two tert-butyl anions at the magnesium center and incorporated lithium chloride.     

A Reactive Molecular Dynamics Study of Chlorinated Organic Compounds. Part I: Force Field Development

This work presents a novel parametrization for the ReaxFF formalism as a means to investigate reaction processes of chlorinated organic compounds. Force field parameters cover the chemical elements C, H, O, Cl and were obtained using a novel optimization approach involving relaxed potential energy surface scans as training targets. The resulting ReaxFF parametrization shows good transferability, as demonstrated on two independent ab initio validation sets. While this first part of our two-paper series focuses on force field parametrization, we apply our parameters to the simulation of chlorinated dibenzofuran formation and decomposition processes in Part II.     

ChemInform Abstract: La3BaSi5N9O2:Ce3+ — A Yellow Phosphor with an Unprecedented Tetrahedra Network Structure Investigated by Combination of Electron Microscopy and Synchrotron X‐Ray Diffraction.

Agglomerates of a few μm of the yellow phosphor La₃BaSi₅N₉O₂:Ce³⁺ are obtained by heating a mixture of LaF₃, La(NH₂)₃, BaH₂, Si(NH)₂, and CeF₃ in a radio frequency furnace under N₂ (1600 °C, 10 h; cooling to 900 °C within 44 h).     

Computer-Driven Development of Ylide Functionalized Phosphines for Palladium-Catalyzed Hiyama Couplings

Palladium-catalyzed couplings of silicon enolates with aryl electrophiles are of great synthetic utility, but often limited to expensive bromide substrates. A comparative experimental study confirmed that none of the established ligand systems allows to couple inexpensive aryl chlorides with α-trimethylsilyl alkylnitriles. In contrast, ylide functionalized phosphines (YPhos) led to encouraging results. A statistical model was developed that correlates the reaction yields with ligand features. It was employed to predict catalyst structures with superior performance. With this cheminformatics approach, YPhos ligands were tailored specifically to the demands of Hiyama couplings. The newly synthesized ligands displayed record-setting activities, enabling the elusive coupling of aryl chlorides with α-trimethylsilyl alkyl nitriles. The preparative utility of the catalyst system was demonstrated by the synthesis of pharmaceutically meaningful α-aryl alkylnitriles, α-arylcarbonyls and biaryls.     

Manganese(I) Catalyzed ortho C−H Allylation of Benzoic Acids

The 3d-metal catalyst Mn(CO)₅Br was found to efficiently promote ortho C−H allylations of arenecarboxylates in the presence of neocuproine as the ligand. Despite the simplicity of directing group and catalyst system, the selectivity goes well beyond the state-of-the-art in that mono-allylated products are obtained exclusively with high selectivities for the least hindered ortho-position. The directing group can optionally be removed by in situ decarboxylation, opening up a regioselective entry to allyl arenes. The preparative utility of the process and its othogonality to other approaches was demonstrated by 44 products with otherwise hard-to-access substitution patterns, including 3-bromo-allylbenzene, 3-allylbenzofuran, or 5-allyl-2-methylnitrobenzene.     

Synthesis of Complex Thiazoline-Containing Peptides by Cyclodesulfhydration of N-Thioacyl-2-Mercaptoethylamine Derivatives

Herein we report a mild, efficient, and epimerization-free method for the synthesis of peptide-derived 2-thiazolines and 5,6-dihydro-4H-1,3-thiazines based on a cyclodesulfhydration of N-thioacyl-2-mercaptoethylamine or N-thioacyl-3-mercaptopropylamine derivatives. The described reaction can be easily carried out in aqueous solutions at room temperature and it is triggered by change of the pH, leading to complex thiazoline or dihydrothiazine derivatives without epimerization in excellent to quantitative yields. The new method was applied in the total synthesis of the marine metabolite mollamide F, resulting in the revision of its stereochemistry.     

Fluorinated Analogues to the Pentuloses of the Pentose Phosphate Pathway

Fluorinated carbohydrates are valuable tools for enzymological studies due to their increased metabolic stability compared to their non-fluorinated analogues. Replacing different hydroxyl groups within the same monosaccharide by fluorine allows to influence a wide range of sugar–receptor interactions and enzymatic transformations. In the past, this principle was frequently used to study the metabolism of highly abundant carbohydrates, while the metabolic fate of rare sugars is still poorly studied. Rare sugars, however, are key intermediates of many metabolic routes, such as the pentose phosphate pathway (PPP). Here we present the design and purely chemical synthesis of a set of three deoxyfluorinated analogues of the rare sugars d -xylulose and d -ribulose: 1-deoxy-1-fluoro-d -ribulose ( 1DFRu ), 3-deoxy-3-fluoro-d -ribulose ( 3DFRu ) and 3-deoxy-3-fluoro-d -xylulose ( 3DFXu ). Together with a designed set of potential late-stage radio-fluorination precursors, they have the potential to become useful tools for studies on the complex equilibria of the non-oxidative PPP.