Stereoselective skeletal modification of tryptanthrins to install chiral piperidine-2-ones enabled by Brønsted acid catalysis

An asymmetric formal [4 + 2] cyclisation between azlactones and aza-dienes derived from simple tryptanthrins has been developed. With this established protocol, yielding a series of novel piperidine-2-one-fused tryptanthrins with up to >99 : 1 er under mild conditions.