Florian Kniep

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The organocatalytic asymmetric α-alkylation of aldehydes by 1,6-conjugated addition of enamines to p-quinone methides is described. Employing a newly developed class of chiral secondary amine catalysts, α-diarylmethine-substituted aldehydes with two contiguous stereocenters have been synthesized in a simple manner with good diastereocontrol and excellent(More)
A well-defined three-point interaction based solely on halogen bonding is presented. X-ray structural analyses of tridentate halogen bond donors (halogen-based Lewis acids) with a carefully chosen triamine illustrate the ideal geometric fit of the Lewis acidic axes of the former with the Lewis basic centers of the latter. Titration experiments reveal that(More)
A novel organocatalytic activation mode of cyclopropanes is presented. The reaction concept is based on a design in which a reactive donor-acceptor cyclopropane intermediate is generated by in situ condensation of cyclopropylacetaldehydes with an aminocatalyst. The mechanism of this enamine-based activation of cyclopropylacetaldehydes is investigated by the(More)
We have conducted isothermal calorimetric titrations to investigate the halogen-bond strength of cationic bidentate halogen-bond donors toward halides, using bis(iodoimidazolium) compounds as probes. These data are intended to aid the rational design of halogen-bond donors as well as the development of halogen-bond-based applications in solution. In all(More)
Halogen bonding is the formation of a non-covalent interaction between an electrophilic halogen substituent and a Lewis base, for instance, a halide. These kinds of relatively weak interactions have found applications in crystal engineering and initial applications in solution-phase chemistry are starting to appear. We report on the exploration of(More)
PURPOSE To evaluate the use of a needle guide for CT guided puncture for the reduction of radiation dose of the interventional radiologist. MATERIAL AND METHODS A total of 20 CT-guided punctures was performed. An approach from anterior was used in 12 cases and an approach from lateral was used in 8 cases. We evaluated the practicability, the precision and(More)
Using a prototypical Diels-Alder reaction as benchmark, we show that dicationic halogen-bond donors are capable of activating a neutral organic substrate. By various comparison experiments, the action of traces of acid or of other structural features of the halogen-bond donor not related to halogen bonding are excluded with high certainty.