Natural products derived from oxidative dimerzation or rearragement of indole motifs are prevalent in many families of compounds. During a synthesis toward one of such compounds, namely Trigonoliimide, a group of chemists observed the following hydroxyl migration reaction between the two indole systems under Lewis acidic conditions as shown:
Propose a mechanism for the above migration. (Hint: a pentacyclic intermediate is present)
For reference:
Qi, Xiangbing; Bao, Hongli; Tambar, Uttam K. Tambar. (2011).
Total Synthesis of (±)-Trigonoliimine C via Oxidative Rearrangement of an Unsymmetrical Bis-Tryptamine.
Journal of the American Chemical Society, 133(26), 10050–10053.
doi:10.1021/ja203960b