Photocatalytic Isomerization of (E)-Anethole to (Z)-Anethole

Natural product (E)-anethole was isomerized to (Z)-anethole in a photocatalytic reaction. For this purpose, a self-designed cheap photoreactor was constructed. Among 11 photosensitizers (organo and metal complex compounds), Ir(p-tBu-ppy)(3) led to the highest conversion. Triplet energies of (E)- and (Z)-anethole were predicted theoretically by DFT calculations to support the selection of appropriate photosensitizers. A catalyst loading of 0.1 mol% gave up to 90% conversion in gram scale. Further additives were not required and mild irradiation with light of 400 nm overnight was sufficient. As a proof of concept, (E)- and (Z)-anethole were dihydroxylated diastereoselectively to obtain diastereomerically pure like- and unlike-configured diols, respectively.

Automated summary

In this study, natural product (E)-anethole was successfully isomerized to (Z)-anethole using a self-designed cheap photoreactor. The selection of an appropriate photosensitizer, Ir(p-tBu-ppy)(3), was supported by theoretical predictions of the triplet energies of (E)- and (Z)-anethole. The reaction achieved high conversion with a catalyst loading of only 0.1 mol% and mild irradiation conditions. Diastereomerically pure diols with different configurations were obtained through dihydroxylation.