Intramolecular Cyclization of Enamines to 3H-Indoles Mediated by Iodine

Significance

Reported is an unexpected intra-molecular cyclization of aromatic enamines promoted by elemental iodine. An extensive investigation of conditions regarding base, solvent, and oxidant was carried out. In the absence of either base or oxidant (or both) the reaction did not proceed. IBr and PIDA afforded the desired product as well albeit in lower and extremely low yields, respectively. No reaction took place in the presence of PIFA. The substrate scope was quite well studied and notably meta-substituted enamines gave mixtures of products. A general iodocyclization pathway was initially proposed but was later discarded based on mechanistic studies.