Total Synthesis of Indigotinoline A and Enabled Stereochemical Revision of Isatindigotindoline B

The first total synthesis of scarce alkaloid indigotinoline A from Isatis indigotica was achieved in six steps from a known carboxylic acid (13% overall yield). The distinctive 6/5/6/5/6 N, O -heterocycle was efficiently assembled via a one-pot triple cascade, Povarov-type cyclization, intramolecular substitution, and visible-light-mediated oxidative rearrangement, followed by bioinspired N-oxidation/1,2-migration. This synthesis also prompted re-examination of proposed biosynthetic precursor isatindigotindoline B, leading to revision of its stereochemistry based on spectroscopic analysis.