Photocatalytic Isomerization of ()-Anethole to ()-Anethole.

Natural product ()-anethole was isomerized to ()-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-Bu-ppy) led to the highest conversion. Triplet energies of ()- and ()-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, ()- and ()-anethole were dihydroxylated diastereoselectively to obtain diastereomerically pure - and -configured diols, respectively.