The Unique Character of Copper in Photoredox Catalysis

This work provides further developments in the field of copper photoredox catalysis underpinning the unique character of copper in such transformations. Several visible-light mediated protocols have been developed during this study: First, a protocol for the rapid chlorosulfonylation of miscellaneous alkenes and alkynes is reported. Besides the Cu(I)-complex [Cu(dap)2]Cl, now well-established in such ATRA processes, the corresponding Cu(II)-complex [Cu(dap)Cl2] proved to be often even more efficient in the title reaction, being advantageous from an economic point of view but also opening up new avenues in copper photoredox catalysis. Moreover, those outperformed commonly used ruthenium-, iridium- or organic dye-based photocatalysts, owing to their ability to stabilize and interact with transient radical intermediates in their inner-coordination sphere. Furthermore, the protocol excels through high yields utilizing commercially available substrates and can be smoothly scaled to gram-quantities of product. The latter can be quantitatively transformed upon elimination giving rise to their corresponding vinyl sulfones, which are of great importance in several fields in synthetic organic as well as medicinal chemistry. The next chapter introduces for the first time the Cu(II)-complex [Cu(dmp)2Cl]Cl as an oxidation- and bench-stable photocatalyst for activation by visible-light-induced homolysis (VLIH) to undergo Cu(I)-photoredox catalysis. The complex is highly efficient and considerably more cost-effective compared to previously established Cu(I) photocatalysts as it is synthesized from commercially available starting materials in one step. Its performance and efficiency are demonstrated within a broad scope of atom transfer radical addition (ATRA) reactions, allowing rapid 1,2 difunctionalization of alkenes, as well as for decarboxylative coupling, for a photocatalytic Appel reaction and for photochemical allylation reactions. Moreover, the utility of the catalyst is presented by gram-scale functionalizations of styrene, thus suggesting [Cu(dmp)2Cl]Cl to be a low-priced alternative catalyst. Furthermore, this study provides UVvis evidence on the mechanism for the VLIH activation of Cu(II)-complexes opening up novel avenues for photocatalysis. The third chapter of this work reports a visible-light mediated copper-catalyzed protocol enabling the highly economic 1,2-difunctionalization of olefins utilizing the readily available and low-cost bulk chemical iodoform. Although this reaction seems to be simple on paper, it turned out that the title transformation is not feasible via commonly employed ruthenium-, iridium- or organic dye-based photocatalysts, thus undergirding the unique role of copper in photoredox catalysis owing to its ability to interact and stabilize incipient radical intermediates in the inner-coordination sphere. The developed protocol is characterized by high yields under environmentally benign reaction conditions and allows for the regio- and chemoselective functionalization of activated double bonds as well as for late-stage functionalization of bioactive molecules. Furthermore, the protocol can be smoothly scaled to gram-quantities of product, which offers manifold possibilities for further transformations, including heterocycle synthesis, intramolecular cyclopropanation or the synthesis of functionalized gem-diiodides being privileged building blocks in organic synthesis but usually challenging to access. In the last chapter a catalyst- and metal-free visible-light mediated iodoamination of miscellaneous alkenes through in-situ activation of sulfonamides with NIS is described. The protocol excels through high yields under environmentally benign reaction conditions utilizing commercially available substrates and a green and biodegradable solvent. Furthermore, the protocol allows for late-stage functionalization of bioactive molecules and can be smoothly scaled to gram quantities of product, which offers a plethora of possibilities for further transformations including the synthesis of 1,2-functionalized amines, enamines or various heterocycles like morpholines, piperidines, pyrrolidines and aziridines