Visible-light-induced mild, transition metal, base, and photocatalyst-free green protocol has been developed for the synthesis of tryptanthrin and its derivatives. The present reaction is compatible with a wide range of substrates with good to high yields. Further, a novel synthetic transformation of tryptanthrin derivatives has been achieved by the decarboxylative addition of cyanoacetic acid for the first time. This reaction proceeds by visible-light-induced single electron transfer between the substrate and oxygen, followed by intramolecular cyclization without the use of an external photocatalyst.

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-(1H-indol-3-ylsulfanyl)-phenylamines and aryl methyl ketones using an efficient catalytic system of I2/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.