Abstract A practical, mild and efficient protocol for the Pictet–Spengler reaction catalyzed by cyanuric chloride (trichloro-1, 3, 5-triazine, TCT) is described. The 6-endo cyclization of tryptophan/tryptamine and modified Pictet–Spengler substrates with both electron- withdrawing and electron-donating aldehydes was carried out by using a catalytic amount of TCT (10 mol%) in DMSO under a nitrogen atmosphere. TCT catalyzed the Pictet– ...