An evaluation study of various palladium supports led to the selection of charcoal as the most efficient system for the preparation of oxindoles by sequential Heck-reduction-cyclization (HRC) reactions. The in situ prepared Pd0/C was not recyclable for further cross-coupling reactions but remains still highly active for reduction processes. The sustainable chemistry described herein allows extremely simple experimental protocol Under mild conditions, free of any base, ligand and additive. (C) 2009 Elsevier Ltd. All rights reserved.
Room-Temperature, Ligand- and Base-Free Heck Reactions of Aryl Diazonium Salts at Low Palladium Loading: Sustainable Preparation of Substituted Stilbene Derivatives
excellent stereoselectivity. The environmentally friendly protocol developed in this work features low palladium loading in technical‐grade methanol at room temperature under base‐, additive‐, and ligand‐free conditions. The same protocol applied to simple Heck coupling of aryl diazonium salts with methyl acrylate allows astonishingly low palladium loading, down to 0.005 mol %. The stereoselectivity experimentally