“…The Pictet–Spengler reaction is catalyzed by Brønsted acids, as they convert the intermediate imine to the corresponding iminium ion, thus making it more electrophilic [18–22]. Conventionally, TFA [18], HCl [20], H 2 SO 4 [21] and p -TsOH [22] are employed as Brønsted acids. However, recently several other aprotic or Lewis acids, such as Yb(OTf) 3 [23–25], AuCl 3 /AgOTf [26], Me 3 SiCl [27–28], BF 3 ·Et 2 O [29], iodine [30], zeolite [31] and enzymes [32–34], have been used for carrying out the Pictet–Spengler reaction.…”