The thesis is divided into 4 chapters which include first an overview of transition-metal catalyzed carbon-carbon cross-coupling and homocoupling reactions based on highly functionalized novel quinolones.
In addition, some recent literature related to C-C coupling reactions is discussed. Second, functionalized 4,4′-bisquinolones can be efficiently synthesized by microwave-assisted palladium(0)-catalyzed one-pot borylation/Suzuki cross-coupling reactions, or via nickel(0)-mediated homocouplings of 4-chloroquinolin-2(1H)-one precursors. Both methods are also applicable to other types of symmetrical biaryls. Third, a method for the gram-scale preparation of functionalized 4,4-bisquinolones using a microwave-assisted Ullmann-type homocoupling reaction is described. The method is catalytic in nickel(0) which is generated in situ by reduction from an inexpensive Ni(II) source and utilizes readily available 4-chloroquinolin-2(1H)-ones as starting materials. In contrast to the alternative palladium(0)-catalyzed one-pot borylation/Suzuki cross-coupling reaction, the new method avoids the use of an expensive catalyst and cross-coupling partner such as bis(pinacolato)diboron.
Biscarbostyrils (4,4'-bisquinolones) can be synthesized from 4-chloro-2-quinolinones using a Pd-catalyzed one-pot borylation/Suzuki cross-coupling protocol or via Ni(0)-mediated reductive homocoupling.
Fourth, the electronic spectra of biscarbostyrils, which exhibit unusual properties in comparison to the corresponding carbostyrils, were examined. Similar absorption spectra are accompanied by red-shifted emission maxima up to 520 nm. Unsubstituted biscarbostyril displays the unusual property of a blueshift in dimethylsulfoxide as compared to water. For a set of diversely substituted biscarbostyrils and related 4-aryl-2-quinolinones very selective substitution patterns in order to increase fluorescence quantum yields are observed. In bisquinolones, an additional diphenylphosphinoxide substitution in position 3 and 3 increased the quantum yield to 0.2 and the epsilon value to 25000. A crown ether linkage from position 6 to 6 in biscarbostyrils improved the emission maximum from 470 to 500nm, but the fluorescence quantum yield only from 0.03 to 0.06. Time-dependent density functional calculations of absorption and emission spectra of selected derivatives show good agreement with the corresponding experimental data.
Especially, the large Stoke's shift observed for biscarbostyrils as well as their rather low fluorescence quantum yields can be rationalized on the basis of these calculations. Like 1,1 binaphthalenes the biscarbostyril structures are axially chiral. Most of the enantiomers were baseline HPLC separated on the Pirkle type ULMO column, with separation factors of up to 2.5. As expected for this pi-acidic chiral stationary phase electron donating methoxy substituents improve separation behavior.