Synthese von 1,2,4-Oxadiazolen, Cyclooctinen und Studien zur Synthese nicht-symmetrischer partiell-fluorierter DNTT

In the first part of this thesis, a novel cycloaddition towards 1,2,4-oxadiazoles is described. The cycloaddition is catalysed by silver triflate using various silyl nitronates and nitriles. A variety of functional groups on the nitrile is tolerated. Using alkenyl and aryl silyl nitronates the method can be employed successfully, while unactivated alkyl silyl nitronates are less efficient. Mechanistic studies were preformed and suggest an elimination of tert-butyl(dimethyl)silanol (TBSOH) after the cycloaddition and without interconversion into the respective nitrile oxide. The described method was successfully applied to the synthesis of a precursor for the drug Ataluren. In the second part of the thesis, the synthesis of different cyclooctynes is described. Ethynylcyclooctyne and a diazide were applied for a chemoselective sequence of strain-promoted azide-alkyne cycloaddition (SPAAC) and copper(I)-catalysed azide-alkyne cycloaddition (CuAAC) on a cholic acid-derived triazide molecular surface material. Chemoselectivity was achieved balancing three factors: Copper-catalysis / ring strain / steric shielding. Further investigation on Si(001) by means of x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) indicate a chemoselective adsorbtion via a [2+2]-cycloaddition of cyclooctyne without side reactions of the ethynyl group. In the third part of the thesis, studies towards the synthesis of symmetrical and non-symmetrical fluorinated DNTT derivatives are presented. The synthesis of a non-fluorinated naphthalene was achieved successfully. Towards the studies of fluorinated naphthalenes a variety of different partially-fluorinated naphthalene patterns were synthesised and characterised. During the studies the synthesis of hexafluoronaphthalene was achieved. First insights towards the coupling of these naphthalene derivatives using Stille- and Liebeskind-cross-coupling were gathered.