Chromoselective Photocatalysis Enables Stereocomplementary Biocatalytic Pathways**

Abstract

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 (<i>S</i>)- or the (<i>R</i>)-enantiomer of phenylethanol. In combination with an unspecific peroxygenase from <i>Agrocybe aegerita</i>, green light irradiation of CN-OA-m led to the enantioselective hydroxylation of ethylbenzene to (<i>R</i>)-1-phenylethanol (99 % <i>ee</i>). In contrast, blue light irradiation triggered the photocatalytic oxidation of ethylbenzene to acetophenone, which in turn was enantioselectively reduced with an alcohol dehydrogenase from <i>Rhodococcus ruber</i> to form (<i>S</i>)-1-phenylethanol (93 % <i>ee</i>).