Discovery and development of novel enantioselective C(sp3)-H functionalisations

This thesis describes studies towards new enantioselective C–H activation reactions. In chapter 2 the investigation towards a novel enantioselective cobalt-catalysed C(sp3)–H alkenylation, directed by thioamides, with but-2-ynoates is described. In this method prochiral thioamides undergo asymmetric C(sp3)–H functionalisation with but-2-ynoates in presence of a [Cp*Co(MeCN)3][SbF6]2 complex and chiral carboxylic acid, which allows the formation of chiral thioamides. The method provides alkenylated products as single regioisomers in excellent yields (up to 85%) and high enantiomeric ratios (up to 91:9 er, or up to >99:1 er after single recrystallisation). The protocol is operationally very simple with mild reaction conditions, which is not very common for C–H functionalisations, because the activation of naturally inactive C–H bonds often requires high reaction temperatures. The applicability of this methodology can be found in diverse downstream derivatisations of products, delivering a broad range of enantiopure pharmaceutically and agrochemically relevant scaffolds, such as various substituted heterocycles. Mechanistic investigations and state-of-the-art DFT calculations carried out in collaboration with Ken Yamazaki, Prof Trevor A. Hamlin and Prof F. Matthias Bickelhaupt revealed that the pivotal C–H activation step is rate- and enantiodetermining step. DFT calculations explain the reaction mechanism, and stereochemical outcome of the products, as well as the unusual regioselectivity of the alkenylation reaction. After successfully developing a novel thioamide-directed cobalt-catalysed enantioselective C(sp3)–H alkenylation reaction, in chapter 3 we investigated intramolecular variant of this new reaction. Taking into consideration the specific interactions between a Cp*CoIII complex, thioamides and but-2-ynoates, with suitable substrates the formation of cyclic products should be straightforward, and this project would be a viable follow-up of our completed study.</p

Relationship between moisture content and electrical impedance of carrot slices during drying

Electrical properties of food materials can give information about the inner structure and physiological state of biological tissues. Generally, the process of drying of fruits and vegetables is followed by weight loss. The aim of this study was to measure the impedance spectra of carrot slices during drying and to correlate impedance parameters to moisture content in different drying periods. Cylindrical slices were cut out from the carrot root along the axis. The slices were dried in a Venticell 111 air oven at 50°C. The weight of the slices was measured with a DenverSI-603 electronic analytical and precision balance. The weighing of the samples was performed every 30 min at the beginning of drying and every 60 min after the process. The moisture content of the samples was calculated on wet basis. The magnitude and phase angle of electrical impedance of the slices were mea-sured with HP 4284A and 4285A precision LCR meters in thefrequency range from 30 Hz to 1 MHz and from 75 kHz to 30 MHz,respectively, at voltage 1 V. The impedance measurement was per-formed after weighting. The change in the magnitude of impe-dance during drying showed a good correlation with the change in the moisture content