Iodine-Catalyzed Synthesis of Benzo-β-carbolines through Desulfurative Cyclization of 2-(1 H -Indol-3-ylsulfanyl)-phenylamines with Aryl Methyl Ketones.

A novel transition metal-free strategy for the synthesis of benzene-fused β-carboline scaffolds has been developed. This protocol offers a rapid and direct pathway to access the benzene fused β-carboline from 2-(1 H -indol-3-ylsulfanyl)-phenylamines and aryl methyl ketones using an efficient catalytic system of I ₂ /DMSO. The present mild protocol proceeds through the sequential reactions of Kornblum oxidation, Pictet-Spengler cyclization, and desulfurization to afford the desired products in excellent yields up to 99%. Moreover, this method has a wide range of substrate tolerance and is operationally simple and applicable in gram-scale synthesis.