This dissertation presents innovative strategies for the transformation of cyclopropanes into complex bicyclic structures containing oxygen and nitrogen, using visible-light photocatalysis and Lewis acid catalysis. The first part of the work explores the synthesis of endoperoxides from cyclopropanated indenes using visible-light activation and acridinium-based organic photocatalysts. By introducing a novel phosphoric acid counteranion, the photocatalytic ring-expansion could be significantly optimized, leading to yields of up to 80% while maintaining stereoselectivity. The resulting endoperoxides are of interest due to their structural similarity to antimalarial agents like Artemisinin, highlighting their potential as leads in drug development. In another part, donor–acceptor-substituted cyclopropanes were subjected to a Lewis acid-mediated ring-opening followed by a cyclization cascade with thioureas. This process led to the formation of fused bicyclic lactam structures such as furo-, pyrano-, and pyrrololactams, which are motifs commonly found in biologically active natural products. Mild reaction conditions, good substrate scope, and mechanistic insights demonstrate the synthetic utility of the method. The work underlines the versatility of cyclopropanes as building blocks in organic synthesis and contributes to the advancement of environmentally friendly approaches for the construction of complex molecules with pharmacological relevance.
Andreas Ratzenböck (Thu,) studied this question.