Stereoselective Direct N-Trifluoropropenylation of Heterocycles with a Hypervalent Iodonium Reagent

The availability and synthesis of fluorinated enamine derivatives such as N-(3,3,3-trifluoropropenyl)heterocycles are challenging, especially through direct functionalization of the heterocyclic scaffold. Herein, a stereoselective N-trifluoropropenylation method based on the use of a bench-stable trifluoropropenyl iodonium salt is described. This reagent enables the straightforward trifluoropropenylation of various N-heterocycles under mild reaction conditions, providing trifluoromethyl enamine type moieties with high stereoselectivity and efficiency.     

Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators

Addition of the P−H bond in bis(mesitoyl)phosphine, HP(COMes)₂ (BAPH), to a wide variety of activated carbon–carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R−P(COMes)₂, under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)₂ can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)₂, a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.     

Correction to: There is at most one continuous invariant mean

Aequationes mathematicae - A mistake in the formulation of Lemma 1 has been corrected. A preliminary section to the proof of Theorem 1 is added.     

Investigation of the regeneration of the passive surface oxide layer of TiAl6V4 alloy printed by WAAM technology using different electrochemical test methods

The kinetics of oxide layer formation on surface of Ti6Al4V alloy samples is a very important property especially if their application as medical implants is planned. Damaged protective surface layer usually heals in ambient condition however; during the self-healing process toxic species can get into the surrounding living tissue. In our experiment the kinetics of the healing process proceeding at 3D printed alloy surface has been studied using electrochemical methods, among them scanning electrochemical microscopy. More than 40 min. time period was found long enough for total healing.     

Polarization energies,transport gap and charge transfer states of organic molecular crystals

A self-consistent calculation of electronic polarization in organic molecular crystals and thin films is presented in terms of charge redistribution in nonoverlapping molecules in a lattice. The polarization energies P₊ and P₋ of a molecular cation and anion are found for anthracene and perelynetetracarboxylic dianhydride (PTCDA), together with binding energies of ion pairs and transport gaps of PTCDA films on metallic substrates. The 500 meV variation of P₊+P₋ with film thickness agrees with experiment, as do calculated dielectric tensors. Comparisons are made to submolecular calculations in crystals.     

Late-Stage Formal Double C−H Oxidation of Prenylated Molecules to Alkylidene Oxetanes and Azetidines by Strain-Enabled Cross-Metathesis

Prenylation is a ubiquitous late-stage modification in nature that often confers significantly improved bioactivity for secondary metabolites. While this lipophilic modification renders enhanced potency, the lipophilic tag(s) can diminish bioavailability and adversely alter drug transportation and metabolism. Thus, a functional-group-tolerant, mild, and selective late-stage C−H functionalization of prenyl tags would present a great potential in drug discovery programs but could also impact other fields, such as agrochemistry and chemical biology. Herein we report an exocyclic-strain-driven cross-metathesis reaction of prenyl tags, a formal double C−H oxidation protocol, that can be used for the selective late-stage derivatization of prenylated compounds and natural products. This methodology avoids the need for prefunctionalization of target molecules and affords ready access to an unprecedented library of oxo- and aza-prenylated complex molecules. Thus, in a broader context, this methodology extends late-stage functionalization beyond that available to nature.