Aerobic oxidative EDA complex mediated photoreactions

Licentiate thesis, 2021

Visible light is a convenient energy source for driving chemical reactions. Its lower energy, compared to ultraviolet irradiation, can be utilized to conduct organic reactions under mild conditions. During the last decades, the growing field of photoredox catalysis has proved this statement true, and a wide variety of radical reactions to form complex molecules has been developed. The photoredox catalysis cycle is typically based on photoactive transition metal complexes. Albeit being highly efficient in the conversion of light energy to chemical energy, these complexes suffer from drawbacks such as the scarcity of the metals. One solution to this problem is to use catalysts based on purely organic compounds. Another way of circumventing the use of catalysts altogether is to take advantage of electron donor acceptor (EDA) complexes. These molecular aggregates are formed when an electron rich molecule interact with an electron deficient partner. Given the right electronic properties of the two reactants, the EDA complex can be excited using visible light and thus induce a chemical reaction without the need of an external catalyst. Oxidative reactions are essential in organic chemistry, and a range of oxidants are available. However, several oxidants rely on transition metals or are highly reactive and toxic. Air, with its high concentration of molecular oxygen, could be considered an ideal oxidant based on the availability, non-toxicity, and the formation of water as the byproduct. In this thesis, the combination of photoactive EDA complexes to induce chemical reactions, with aerobic oxygen as an oxidant, is investigated. Two protocols for the visible light driven synthesis of substituted tetrahydroquinolines (THQ) have been developed. The reactions are driven by the excitation of photoactive EDA complexes formed between N,N-dialkylated anilines as donors and activated alkenes as acceptors. Aerobic oxygen drives the net-oxidative reactions to the final products. The mild reaction conditions, cheap and accessible reagents, and the excellent diastereoselectivity make the presented protocols attractive for the synthesis of the THQ scaffold.