While some natural products contain chiral thiols and thioethers, the strategy for their synthesis in nature either relies on the asymmetric enzymatic synthesis of other functional groups (such as epoxides) followed by substitution, or the use of radical enzymes. These enzymes are typically very substrate specific, and thus do not appear promising as general biocatalysts in a synthetic organic chemistry context. Recently, several classes of enzymes have been shown to be able to control non-native radical chemistries, such as ene-reductases (EREDs) by the Hyster group, pyridoxal 5-phosphate (PLP)dependent enzymes by the Yang group (Figure ), and other examples. These strategies typically rely on light to generate radicals, either by accessing excited states of cofactors (e.g. flavin mononucleotide (FMN) in EREDs), or by supplying an exogenous photocatalyst. This light requirement comes with serious disadvantages, such as known photodegradation of the light-sensing chromophore, as well as light-penetration during process scale-up/intensification. Remarkably, some EREDs do not require light to access single electron chemistries with αbromoacetophenones, generating reactive α-acyl radicals that have been shown to react with styrenes. In the case of pro-chiral styrenes, such as α-methyl styrene, the benzylic radical intermediate formed after radical addition to the double bond is terminated via a highly enantioselective hydrogen atom transfer (HAT) from the FMN cofactor; however, larger substituents than methyl or ethyl have been reported to give only traces of conversion. Inspired by this reaction, we envisaged that radical addition to prochiral vinyl sulfides followed by enantioselective HAT would generate chiral thioethers (Figure ). This strategy requires the enzyme to accept the large size of the sulfur substituent at the double bond, and control both the reactive α-acyl radical intermediate as well as the orientation of the co-substrate to prevent unselective radical chemistries occurring at the sulfur. 27