Palladium-Mediated Oxidative Annulation of δ-Indolyl-α,β-Unsaturated Compounds toward the Synthesis of Cyclopenta[b]indoles and Heterogeneous Hydrogenation To Access Fused Indolines

Authors:            

Agy, Andre Capretz ¹ ; Rodrigues, Jr., Manoel T. ¹ ; Zeoly, Lucas A. ¹ ; Simoni, Deborah A. ² ; Coelho, Fernando ¹

Abstract:

The cyclopenta[b]indole moiety represents a key skeletal unit in several natural and synthetic compounds that exhibit diverse biological properties. We described herein a two-step sequence for synthesizing cyclopenta[b]indoles with great structural diversity in overall yields up to 37%. The key step was a palladium-catalyzed oxidative annulation of 3-alkylindoles (Fujiwara–Moritani reaction). The obtained cyclopenta[b]indoles were used as substrates in heterogeneous hydrogenation reactions to afford new fused indolines in moderate yields. An acid-catalyzed intramolecular cyclization of three such indolines gave tetracyclic lactams in 89, 90, and 61% yields.

¹   University of Campinas, Institute of Chemistry, Laboratory of Synthesis of Natural Products and Drugs, P.O. Box 6154, 13083-979 Campinas, SP, Brazil

²   University of Campinas, Institute of Chemistry,  Laboratory of Crystallography, P.O. Box 6154, 13083-979 Campinas, SP, Brazil

Link to article:   https://pubs.acs.org/doi/10.1021/acs.joc.9b00505