The researcher also worked on generation of aryl carboxyl radical intermediate via VLIH of a ArCOO-Cu(II) complex which would add to an alkyne to produce vinyl radical intermediate. If this is possible, the vinyl radical can undergo cascade cyclization divergently depending on the reaction conditions to produce spirolactone dienone compounds and isocoumarin analogs. Despite several trials taking benzoic acid and phenylacetylene as model substrate, we have failed to achieve the target molecules with varying different reaction parameters. A deep dive into the photocatalytic cycle has led to the conclusion that the reoxidation of Cu(I) to Cu(II) to close the catalytic cycle could not take place in the absence of an external oxidant. In this context, we thought electrochemical anodic oxidation of Cu(I) to Cu(II) could solve this longstanding issue. However, combining benzoic acid and phenylacetylene through electrochemical paired electrolysis, led to a completely different product 2-methyl-3,6-diphenylpyridine and this outcome incited us to explore more, and we could publish the work in a high-impact journal, Angew. Chem. Int. Ed. 2024, doi.org/10.1002/anie.202411930. However, we still aim to find an alternative to the terminal reoxidation step of the Cu(II)-photocatalytic cycle by combining anodic oxidation with the VLIH process to accomplish an overall catalytic pathway avoiding stoichiometric external oxidant.
Heteroleptic Cu(I)-complexes (synthesis of heteroleptic CuII-complexes are difficult) were not suitable for the enolate oxidation process, however, they could be efficiently utilized for olefin difucntionalization e.g. β-chloroacylation of alkenes and alkynes (10.26434/chemrxiv-2024-kzmzm-v2; submitted in Nature Catalysis).
