Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst

A bifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO₂-L is obtained by pyrolysis of a cobalt-impregnated composite followed by subsequent selective leaching. In the presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal–Knorr/Clauson-Kass condensation provides >40 pyrroles in good to high yields using dihydrogen, formic acid, or a CO/H₂O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co-catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)-Isamoltane.     

False theta functions and companions to Capparelli's identities

Capparelli conjectured two modular identities for partitions whose parts satisfy certain gap conditions, which were motivated by the calculation of characters for the standard modules of certain affine Lie algebras and by vertex operator theory. These identities were subsequently proved and refined by Andrews, who related them to Jacobi theta functions, and also by Alladi–Andrews–Gordon, Capparelli and Tamba–Xie. In this paper we prove two new companions to Capparelli's identities, where the evaluations are expressed in terms of Jacobi theta functions and false theta functions.     

Why is cis/trans stereoinversion with Li+(THF)4 migration across the phenyl ring of α-lithiostyrene accelerated by two ortho-methyl groups?

Common wisdom might anticipate that two methyl groups placed on a molecular migration route should act as an impediment. However, the “conducted tour” migration of Li⁺(THF)₄ across the aryl ring (“π-route”) during the cis/trans stereoinversion of α-arylvinyllithiums had been found to occur with practically equal velocities in the presence of either one or two ortho-alkyl substituents. We now report that the omission of both ortho-methyl groups retards the stereoinversion process. In order to arrive at an answer to the title question, we investigate the aggregation equilibria and microsolvation states of ortho, ortho′-unsubstituted α-lithiostyrenes by means of approved secondary NMR criteria. Beyond such necessary knowledge about the ground-state properties, we provide kinetic evidence showing that the retarded cis/trans stereoinversion of α-lithiostyrene proceeds by the pseudomonomolecular, ionic mechanism with Li⁺(THF)₄ migration.     

Development and in-house validation of an LC-MS/MS method for the determination of stilbenes and resorcylic acid lactones in bovine urine

Stilbenes and zeranol are nonsteroidal estrogenic growth promoters which are banned in the European Union (EU) for use in food-producing animals by Council Directive 96/22/EC. A liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was developed for the screening and confirmation of stilbenes (diethylstilbestrol, dienestrol, hexestrol) and resorcylic acid lactones (zeranol and its metabolites taleranol and zearalanone as well as the mycotoxins α-zearalenol, β-zearalenol and zearalenone) in bovine urine. The method permits the confirmation and quantification of stilbenes and resorcylic acid lactones at levels below 1 μg L⁻¹ and 1.5 μg L⁻¹, respectively. The validation was carried out according to Commission Decision 2002/657/EC, Chap. 3.1.3 “alternative validation” by a matrix-comprehensive in-house validation concept. Decision limit CCα, detection capability CCβ, recovery, repeatabiliy, within-laboratory reproducibility and the uncertainty of measurement were calculated. Furthermore, a factorial effect analysis was carried out to identify factors that have a significant influence on the method. Factors considered to be relevant for the method in routine analysis (e.g. operator, matrix condition, storage duration of the extracts before measurement, different cartridge lots, hydrolysis conditions) were systematically varied on two levels. The factorial analysis showed that different cartridge lots, storage durations and matrix conditions can exert a relevant influence on the method.