A Divergent Polyene Cyclization for the Total Synthesis of Greenwayodendrines,Greenwaylactams, Polysin and Polyveoline

We present a concise asymmetric total synthesis (5–8 steps) of nine sesquiterpenoid alkaloids featuring four different tetra-/pentacyclic scaffolds. To this end, a novel, bioinspired indole N-terminated cationic tricyclization has been developed, enabling the divergent synthesis of greenwayodendrines and polysin. Subtle variation of the C2-substituted indole cyclization precursor allowed switching between indole N- and C-termination. For the latter, a subsequent Witkop oxidation enabled conversion of the cyclopentene-fused indole into the eight-membered benzolactam to directly furnish the family of greenwaylactams. In addition, a diastereomeric C-termination product has been elaborated to provide access to polyveoline.     

Exposing the Oxygen-Centered Radical Character of the Tetraoxido Ruthenium(VIII) Cation [RuO4]+

The tetraoxido ruthenium(VIII) radical cation, [RuO₄]⁺, should be a strong oxidizing agent, but has been difficult to produce and investigate so far. In our X-ray absorption spectroscopy study, in combination with quantum-chemical calculations, we show that [RuO₄]⁺, produced via oxidation of ruthenium cations by ozone in the gas phase, forms the oxygen-centered radical ground state. The oxygen-centered radical character of [RuO₄]⁺ is identified by the chemical shift at the ruthenium M₃ edge, indicative of ruthenium(VIII), and by the presence of a characteristic low-energy transition at the oxygen K edge, involving an oxygen-centered singly-occupied molecular orbital, which is suppressed when the oxygen-centered radical is quenched by hydrogenation of [RuO₄]⁺ to the closed-shell [RuO₄H]⁺ ion. Hydrogen-atom abstraction from methane is calculated to be only slightly less exothermic for [RuO₄]⁺ than for [OsO₄]⁺.     

Reductive Cross-Coupling of a Vinyl Thianthrenium Salt and Secondary Alkyl Iodides

We report the first reductive vinylation of alkyl iodides. The reaction uses a vinyl thianthrenium salt, a palladium catalyst, and an alkyl zinc intermediate formed in situ to trap the L_nPd^II(vinyl) complex formed after oxidative addition before it undergoes undesired homocoupling to form butadiene.     

Substitution reactions of gaseous ions in a three‐dimensional quadrupole ion trap

Substitution reactions between gaseous ions and neutral substrate molecules are of ongoing high interest. To investigate these processes in a qualitative and quantitative manner, we have constructed a device, with which a defined amount of a volatile substrate can be mixed with a defined amount of helium gas and added into a three‐dimensional quadrupole ion trap. From the known inner volume of the device, the known ratio n_substrate:n_He of the mixture, and the determined absolute partial pressure of helium in the ion trap, we can derive the partial pressure of the substrate in the ion trap and, thus, convert the directly observable pseudo–first‐order rate constants of the substitution reactions into absolute bimolecular rate constants. We have tested the device by investigating a series of S_N2 reactions of Br ^? and CF₃CH₂O ^? anions as well as ligand exchange reactions of ligated Na⁺ cations. As the obtained results suggest, the described device makes it possible to determine the bimolecular rate constants of substitution reactions as well as other ion‐molecule reactions with satisfactory accuracy and reliability.     

On-Line Coupling of Separation Techniques to NMR

The hyphenation of chromatographic separation techniques with NMR spectroscopy is one of the most powerful and time-saving methods for the separation and structural elucidation of unknown compounds and molecular compositions of mixtures. Most of the routinely used NMR flow-cells have detection volumes between 40–180 μL for conventional separations with analytical columns, and the newest designs employ detection volumes in the order of 200 nL for capillary separations. The low flow rates used in capillary chromatography permit the use of deuterated solvents. Unequivocal structural assignment of unknown chromatographic peaks is possible by two-dimensional stopped-flow capillary HPLC-NMR experiments.     

MaxSynBio: Avenues Towards Creating Cells from the Bottom Up

A large German research consortium mainly within the Max Planck Society (“MaxSynBio”) was formed to investigate living systems from a fundamental perspective. The research program of MaxSynBio relies solely on the bottom‐up approach to synthetic biology. MaxSynBio focuses on the detailed analysis and understanding of essential processes of life through modular reconstitution in minimal synthetic systems. The ultimate goal is to construct a basic living unit entirely from non‐living components. The fundamental insights gained from the activities in MaxSynBio could eventually be utilized for establishing a new generation of biotechnological processes, which would be based on synthetic cell constructs that replace the natural cells currently used in conventional biotechnology.     

Access to the Bis‐benzene Cobalt(I) Sandwich Cation and its Derivatives: Synthons for a “Naked” Cobalt(I) Source?

The synthesis and structural characterization of the hitherto unknown parent Co(bz)₂⁺ (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO₅⁺ salt, or directly from Co₂(CO)₈ and a Ag⁺ salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? {R^F=C(CF₃)₃} and the solvent ortho‐difluorobenzene (o‐DFB). The magnetic properties of Co(bz)₂⁺ were measured and compared in the condensed and gas phases. The weakly bound Co(o‐dfb)₂⁺ salts are of particular interest for the preparation of further Co^I salts, for example, the structurally characterized low‐coordinate 12 valence electron Co(P^tBu₃)₂⁺ and Co(NHC)₂⁺ salts.     

High-Order Numerical Methods for Electromagnetic Induction

The present paper establishes an axisymmetric benchmark model of a conducting loop, which implies an electromagnetic induction. Therein, the fully coupled MAXWELL equations are demonstrated in a monolithic solution strategy. This dynamic problem is solved with a high order finite element discretization using GALERKIN's method in space as well as in time. Furthermore, high order RUNGE-KUTTA time integration methods are analyzed. Studies regarding an h error estimation and the order of convergence are examined. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)