A facile approach for the synthesis of 3,4‐dihydropyrimidin‐2(1H)‐ones was developed by a tandem multi‐component reaction (MCR) in onepot. This approach involves two steps, lipase‐catalyzed in situ generation of acetaldehyde and the Biginelli reaction in turn. Several control experiments were performed using acetaldehydes directly to explore the possible mechanism of this procedure. Moreover, owing