Photoredox Generated Vinyl Radicals: Synthesis of Bisindoles and β-Carbolines

A photoredox catalyzed approach enabling use of alkynes as surrogate of 2-oxoaldehydes/1,2-diones is reported. The method overcomes the difficulty associated with application of unsubstituted aliphatic α-oxoaldehydes, which has hitherto limited their general use. Indoles, tryptamine, and tryptophan methyl ester participated in the reaction to give a variety of α-oxo based analogues. Quantum yield investigations support a radical chain mechanism.