Synthesis of 1,3‐Amino Alcohols by Hydroxy‐Directed Aziridination and Aziridine Hydrosilylation

We describe an approach to N‐tosyl 1,3‐amino alcohols that consists of a diastereoselective aziridination reaction of acyclic allylic alcohols and an unprecedented regioselective hydrosilylation of α‐hydroxy aziridines. The products contain up to three contiguous stereocenters. Computational studies outline key aspects of the aziridination mechanism, which is different and more intricate than anticipated.     

A Simply Synthesized,Tough Polyarylene with Transient Mechanochromic Response

A simple and high‐yielding route to tough polyarylenes of the type poly(meta,meta,para‐phenylene) (PmmpP) is developed. PmmpP is tough even in its as‐synthesized state which has an intermediate molar mass of M_w≈60 kg mol^?1 and exhibits outstanding mechanical properties at further optimized molecular weight of M_w=96 kg mol^?1, E=0.9 GPa, ?=300 %. Statistical copolymers with para,para‐spiropyran (SP) are mechanochromic, and the toughness allows mechanochromism to be investigated. Strained samples instantaneously lose color upon force release. DFT calculations show this phenomenon to be caused by the PmmpP matrix that allows build‐up of sufficiently large forces to be transduced to SP, and the relatively unstable corresponding merocyanine (MC) form arising from the aromatic co‐monomer. MC units covalently incorporated into PmmpP show a drastically reduced half life time of 3.1 s compared to 4.5 h obtained for SP derivatives with common 6‐nitro substitution.     

Intramolecular Aza‐Diels–Alder Reactions of ortho‐Quinone Methide Imines: Rapid,Catalytic, and Enantioselective Assembly of Benzannulated Quinolizidines

Aza‐Diels–Alder reactions (ADARs) are powerful processes that furnish N‐heterocycles in a straightforward fashion. Intramolecular variants offer the additional possibility of generating bi‐ and polycyclic systems with high stereoselectivity. We report herein a novel Brønsted acid catalyzed process in which ortho‐quinone methide imines tethered to the dienophile via the N substituent react in an intramolecular ADAR to form complex quinolizidines and oxazinoquinolines in a one‐step process. The reactions proceed under very mild conditions, with very good yields and good to very good diastereo‐ and enantioselectivities. Furthermore, the process was extended to a domino reaction that efficiently combines substrate synthesis, ortho‐quinone methide imine formation, and ADAR.     

The Influence of β‐diiminato Ligands on As4 Activation by Cobalt Complexes

In a systematic study of the activation of As₄, three [LCo(tol)] (L=β‐diiminato) complexes have revealed different steric and electronic influences. 2,6‐Diisopropylphenyl (Dipp) and 2,6‐dimethylphenyl (dmp) flanking groups were used, one of the ligands with H backbone substituents (β‐dialdiminate L⁰) and two with Me substituents (β‐diketiminates L³ and L¹). In the reaction with As₄, different dinuclear products [(LCo)₂As₄] (LM=L⁰ ( 1 ), L¹ ( 2 ), L³ ( 3 )) were isolated, with all showing differently shaped [Co₂As₄] cores in the solid state: octahedral in 1 , prismatic in 2 , and asterane‐like in 3 . Thermal treatment of 3 leads to the abstraction of one arsenic atom to yield [(L³Co)₂As₃] ( 4 ). All products were comprehensively characterized by single‐crystal X‐ray diffraction, FD‐MS, and ¹H NMR spectroscopy. A rational explanation for the different reactivity is also proposed and DFT calculations shed light on the nature of the highly flexible [Co₂As₄] cores.     

Validating a Single-Particle ICP-MS Method to Measure Nanoparticles in Human Whole Blood for Nanotoxicology

With the rising use of nanomaterials in everyday objects, an uptake of those materials by humans is very likely. To assess their effect on the body, reliable detection of nanoparticles even in very low amounts in human blood becomes increasingly important. Single-particle (SP) inductively coupled plasma–mass spectrometry (ICP-MS) is a fast and reliable method for counting and sizing particles at lowest concentrations, while simultaneously distinguishing between dissolved and particulate analytes. For the first time to our knowledge, a dedicated method validation approach for silver and gold nanoparticle analysis in human whole blood has been performed. With only little sample preparation, trueness expressed as bias with values below or equal to 5% and imprecision values below 6% for particle size as well as an effective limit of detection of around 20?nm are possible. The concentration working range throughout all measured samples was in the nanogram per liter range, making SP-ICP-MS a powerful tool in future nanotoxicological applications and trace analysis of nanoparticles.     

The Radical Ions of Indolizino [6,5,4,3-aij]quinoline and Some of its Derivatives

Indolizino [6,5,4,3-aij]quinoline (1) and its 3,9-dimethyl- (2) , di-tert-butyl- (3) and diphenyl- (4) derivatives yield persistent radical cations which have been studied by ESR and ENDOR spectroscopy. The corresponding radical anions have also been prepared, but only that of 3 was amenable to a complete characterization by hyperfine data. The π-spin populations in the radical anions are essentially localized on the 13-membered C-perimeter, and thus both the HOMO and LUMO of 1 exhibit an ‘annulenyl character’. The radical anions of 1 and 2 have gradually been converted into those of the corresponding 3,4-dihydro derivatives ( 1 -H₂ and 2 -H₂) which have been unambiguously identified by a combination of preparative and spectroscopic methods.     

Dissociative recombination study of Na+ (D2O) in a storage ring

The dissociative recombination of Na(+)(D(2)O) ion has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The cross section has been measured as a function of center-of-mass energy ranging from 1 meV to 0.1 eV and found to have an E(-1.37) dependence. The rate coefficient has been deduced to be (2.3+/-0.32)x10(-7)(T(e)/300)(-0.95+/-0.01) cm(3) s(-1) for T(e)=50-1000 K. The branching ratios have been measured at 0 eV. Of the four energetically accessible dissociation channels, three channels are found to occur although the channel that breaks the weak Na(+)-D(2)O bond is by far dominant.     

Substituent Effects on Site Selectivity (C=C vs C=N) in Heterocumulene-Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

The effect of substituents on the site selectivity (C=C vs C=N) in the [4 + 2] cycloaddition between heterocumulenes (ketene imines) 2a-g with heterodienes (acroleines 9a-n and 4-acylfuran-2,3-diones 1a-d) is treated by semiempirical AM1 molecular orbital and density functional calculations using Becke's three-parameter hybrid method (B3LYP/6-31G). For some reactions calculations were also done at the B3LYP/6-31+G level of theory. For reaction of the oxa 1,3-dienes with ketene imines unsubstituted at the terminal carbon invariably addition across the C=C heterocumulene double bond has a lower activation energy than addition across the C=N double bond. Substitution of methyl or especially phenyl groups at the ketene imine C-terminus leads to a reversal of the respective activation energies. Incorporation of the oxa 1,3-diene system into the heterocyclic dione 1 substantially enhances the reactivity ( approximately 10 kcal mol(-1) lower activation energies) as compared to similarly substituted acroleins. At the DFT level of theory all reactions are found to proceed via a concerted asynchronous mechanism.