Non-typical leaving groups in visible light photocatalyzed C-H fun- tionalization reactions

SOFIA CABY; JAVIER I. BARDAGÍ

Cologne

Simposio; 20th European Symposium on Organic Chemistry (ESOC 2017); 2017

University of Cologne

Visible light photoredox catalysis is emerging as a good alternative in organic synthesis due to the fast growing of the last years. Metal complexes of Ru and Ir are responsible for this development, however it has been demonstrated that organic dyes (for example eosin Y, rhodamine 6G, 10-methylacridinium ions) could be used as well with great success in the synthesis of organic compounds. [1, 2] One of the most explored and useful approach in photoredox catalysis is the generation of radicals by the single electron transfer to suitable substrates. Aryl radicals could be obtained by visible light photoinduced electron transfer (PET) from catalysts. However, in classical approach only electron deficient arenes, such as diazonium salts or some aryl iodides could be used, which is explained by the accessible reducing power of typical visible light photoredox catalysts. Recently, it was demonstrated that it is possible to overcome this by using the energies of two photons by designing an approach that resemble the Z-scheme of natural photosynthesis, in a so called consecutive PET (conPET) (scheme 1, left). [3,4] In this work we explore the conPET approach using substrates with non-typical leaving groups such as Ar-NR3+X- and alcohols for the functionalization of heterocycles poorly explored in visible light photoredoxcatalysis (scheme 1, right). In this examples amines and ?OR are used as leaving groups allowing a more straightforward substitution of alcohols and amines, which are widely distributed in natural product and available in commercial from commercial sources. In an attempt to minimize the environmental impact of the conditions used, mixtures of DMSO with water or alcohols are analysed. The photocatalyzed reaction of PhNR3+X- and N-methylpyrrole give the expected product in DMSO and DMSO:H2O mixtures when rhodamine 6G was used as photocatalysts using a blue LED. Participation of the conPET mechanism is confirmed by the absence of product with a green LED. [4]