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- t Bu-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.