FRESH lecture: Applications of "dual" Metallaphotoredox Catalysis in the Synthesis of Quaternary Carbons
- Monday 28 March 2022
2333 CC Leiden
The synthesis of all-carbon quaternary centres is generally performed using rare and expensive transition metals. The development of more sustainable and accessible routes towards these important scaffolds found in natural products and pharmaceuticals is an important goal. In the last few decades, the combination of photoredox- and transition metal catalysis has proven to open up new synthetic pathways unavailable through conventional catalysis. I report our recent progress in performing allylic substitution reactions to build quaternary centres using dual photoredox/transition metal catalysis. We employed vinyl-substituted cyclic carbonates (VCCs) as versatile and modular allylic surrogates and coupled them reductively to form carbon-carbon bonds. By using different catalysts and substrates, we were able to synthesise functional 1,3-diols, α,β-tetrasubstituted homoallylic alcohols or 1,2-difunctionalised homoallylic alcohols. We are especially interested in the use of cobalt catalysts in such metallaphotoredox-catalytic conversions, as the use of the more abundant first-row transition metals with photoredox catalysts is beneficial over alternatives such as palladium or iridium. By thorough mechanistic analysis of the cobalt-catalysed allylation of aldehydes under photoreductive conditions, we found that key transient inter-catalysts interactions (i.e., between the photoredox catalyst and either the cobalt complex, or base co-catalyst) dictate the efficiency of the reaction. Such interactions are often neglected in literature, but they explain the low quantum yields in metallaphotoredox catalysis that prevent large-scale syntheses.