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Zusammenfassung:
An introduction is given to the topics of photoredox catalysis and intermolecular radical difunctionalizations of alkenes. Radical difunctionalizations transform C–C double (multiple) bonds by generating two new σ bonds in one reaction. Starting from general models in this research field, applications of α-carbonyl and acyl radicals are described. In addition, methodologies, which use the consecutive 1,2-addition of a radical as well as a nucleophile are addressed. An application of artemisinin as a radical co-initiator in acrylamide polymerizations in aqueous medium was developed. The assessment of reaction conditions, leading to the formation and characterization of polymer mixtures is described. Hydrochloric acid as well as iron species are used as co-initiators. Furthermore, results from an electron paramagnetic resonance (EPR) experiment with the initiator system were pointing towards the involvement of a by December 2020 unknown radical in the chemistry of artemisinin. A joined project is discussed, elaborating a method for Brønsted acid catalyzed γ-cyanoketone formations. The difunctionalization implements α-ketonyl radical formation from condensation of ketones with tert-butylhydroperoxide3 and methanesulfonyl cyanide.1 Contributions to learn about the application scope of formed γ-cyanoketones, subsequent transformations and from a noticed difference in diastereoselectivity compared to the previously reported γ-peroxyketone synthesis3 are described.
An investigation of photoredox catalyzed alkene difunctionalization using a consecutive addition of acyl radicals and nucleophilic N-alkylindoles is summarized.2 In the Ir(ppy)3 catalyzed reaction, simple starting materials, namely aldehydes, N-alkylindoles and styrenes were employed. Moreover, a base is needed for successful product formation. The reaction is based on a Ir(III)/Ir(IV) catalytic cycle and tert-butyl perbenzoate as oxidant as well as precursor for tert-butoxyl radicals. Acyl radicals were generated by hydrogen atom transfer. Aryl as well as aliphatic aldehydes were suitable substrates. Investigations of the reaction scope, description of mechanistic indications and discussions the in scientific context are presented.
