Vicinal Diamines as Smart Cosubstrates in the Transaminase‐Catalyzed Asymmetric Amination of Ketones

Transaminases (TAs) have recently been established as catalysts for the asymmetric, reductive amination of prochiral ketones. Depending on the ketone substrate and the amine donor (the cosubstrate), equilibrium constants may limit high conversions; thus, methods to overcome this limitation are required. Removal of the co‐product from the reaction equilibrium through spontaneous, intramolecular reactions has provided a successful solution to this problem; therefore, these amine donors have been named “smart cosubstrates”. Here, we present a comparison of various bifunctional amine donors including vicinal diamines as potential structural cosubstrate motifs. Upon TA‐catalyzed deamination of 1,2‐diamines, spontaneous dimerization of the resulting α‐aminoketones and oxidation gave heteroaromatic pyrazines.