I : Synthèse de carbazole en débit continu. II : Transfert de proton couplé à l’électron photocatalysé au cuivre
Photochemistry and photocatalysis have had a significant impact in organic synthesis, often offering low-energy alternatives to traditional thermal chemistry, or even affording complementary reactivity. The thesis is divided into two sections describing photochemical methods for the synthesis of carbazoles and 1,2-diols. The first section described the conception of a flow chemistry apparatus and a comparison of two photochemical methods, one using visible light and another using UV-light for carbazole synthesis via flow chemistry. While UV irradiation affords better yields, it does not tolerate sensitive functionals groups that are accessible when irradiated in the visible range. The chemoselectivity of the carbazoles synthesis is also examined with both methods. The second section explores the development of copper(I) photocatalysts for promoting a reductive proton-coupled electron transfer (PCET). General guidelines and structure/activity relationships were established for the PCET process through evaluation of a 50-member library of heteroleptic copper complexes bearing one diamine and one bisphosphine. Furthermore, it was demonstrated that a copper photocatalyst could be designed a priori to incorporate a hydrogen-bond donor within its framework to promote PCET reactions. The newly designed catalyst was applied in a photochemical pinacol coupling and was capable of transforming substrates that were unreactive using existing technology, even with a hydrogen bond donor that was orders of magnitude less acidic than common additives. Mechanistic studies demonstrated that the copper catalyst functioned via reductive quenching before PCET, which could not have been easily predicted given the literature precedent. The thesis describes the preparation of molecules such as pinacols and heterocycles that are of high value. Importantly, the new photochemical methods developed lower the energy requirements for synthesis, decrease reaction times and use continuous flow technology that would facilitate and intensify scale-up. In sum, the research herein contributes to efforts to promote sustainable and greener methods of synthesis for fine chemicals.
Carbazoles PCET Photochemistry Flow chemistry Carbazoles Copper