Vinylkationen als reaktive Intermediate

In this work several new reactions based on the reactivity of vinyl cations were developed. In this context we showed that carbonyl compounds like cyclopentanone were able to facilitate the direct addition of alcohols to simple alkynes by stabilizing the corresponding vinyl cations and prevent undesired side reactions.Furthermore, based on these findings, a transition-metal free multicomponent reaction from simple starting materials was developed. In this reaction we demonstrated that the intrinsic high reactivity of a vinyl cation could be moderated by forming a non-classical bicyclic carbocation as useful cascade intermediate with superior stability. Making use of this, we were able to fully diastereoselective synthesize diverse pharmacologically interesting bicyclic amines.Due to the limitation in the synthesis of N-heterocycles based on azides and alkines, a metal-free carboamination reaction was investigated. After an initial C–C-bond formation, a subsequent Schmidt type reaction leads to polysubstituted quinolines once again showing that undesired side reactions can be controlled by a subsequent thermodynamically favored transformation of the vinyl cation. The extrusion of nitrogen followed by aromatization revealed as a powerful driving force for this transformation and allowed even the conversion of poorly nucleophilic aliphatic alkynes and therefore even less stabilized vinyl cations.In the last part of this work, vinyl cations were used to obtain highly reactive α-carbonyl cations. In this case, the generated α-carbonyl cations were even more reactive then the literature described gold-stabilized analogues and could be used for several 1,2-shifts. Beside hydride shifts, also alkyl and aryl shifts were accessible with this method leading to quaternary carbon centers. The formation of an α-carbonyl cation as well as the 1,2-shift were both confirmed by mechanistic investigations. In addition, the 1,2-shift of alkinyl groups was possible which are known to have one of the lowest shift tendency