Gold-Catalyzed Synthesis of 6-, 7- and 8-Membered Heteroannulated Indoles

Significance

Unprecedented regiochemical control of gold-catalyzed heteroannulations to indole rings as a function of the gold oxidation state is reported. Treatment of substrates A with a cationic gold(I) complex results in the formation of azepino[4,5-b]indole derivatives B, while application of the more electrophilic AuCl₃ catalyst leads to indoloazocines D by an 8-endo-dig process. In some cases, formation of allenyl indole byproducts E is observed, suggesting a different catalytic pathway for [Au(III)] than that proposed previously for the [Au(I)] path involving intermediate C (C. Nevado, A. M. Echavarren Chem. Eur. J. 2005, 11, 3155-3164; C. Nieto-Oberhuber, M. P. Muñoz, E. Buñuel, C. Nevado, D. J. Cárdenas, A. M. Echavarren Angew. Chem. Int. Ed. 2004, 43, 2402-2406).