Synthesis of 6-Alkynyl-6-hydroxyindoloquinazolinone Scaffolds via Copper-Catalyzed Alkynylation of Tryptanthrins

We report a copper-catalyzed direct alkynylation reaction of tryptanthrins with terminal alkynes under mild reaction conditions. The developed method provides an array of synthetic building blocks of 6-alkynyl-6-hydroxyindoloquinazolinone compounds in moderate to good yields with varied functional group compatibility. Furthermore, the obtained adducts can be smoothly converted into versatile building blocks via hydrogenation, hydration, and further Sonogashira coupling transformations.