Chromoselective Photocatalysis Enables Stereocomplementary Biocatalytic Pathways.

Controlling the selectivity of a chemical reaction with external stimuli is common in thermal processes, but rare in visible-light photocatalysis. Here we show that the redox potential of a carbon nitride photocatalyst (CN-OA-m) can be tuned by changing the irradiation wavelength to generate electron holes with different oxidation potentials. This tuning was the key to realizing photo-chemo-enzymatic cascades that give either the ( S )- or the ( R )-enantiomer of phenylethanol. In combination with an unspecific peroxygenase from Agrocybe aegerita , green light irradiation of CN-OA-m led to the enantioselective hydroxylation of ethylbenzene to ( R )-1-phenylethanol (99 % ee ). In contrast, blue light irradiation triggered the photocatalytic oxidation of ethylbenzene to acetophenone, which in turn was enantioselectively reduced with an alcohol dehydrogenase from Rhodococcus ruber to form ( S )-1-phenylethanol (93 % ee ).