Palladium-catalysed direct regioselective synthesis of cyclic ketals from electron-rich olefins and aryl bromides in ionic liquids

Abstract

The Heck reaction comprises one of the most important carbon-carbon coupling reactions in organic synthesis. The popularity of the reaction is attributable to the broad availability of aryl halides and to the tolerance of the reaction for a wide variety of functional groups. Reported herein is a direct method for the highly regioselective preparation of 5-membered and 7-membered cyclic ketals in respectable to good yields from aryl bromides (1a-k) and electron-rich olefins (2a and b). The reaction is performed with palladium catalysis using ionic liquid as solvent with no need for any halide scavengers, providing an alternative to the use of aryl triflates. The ionic liquid is found to direct the reaction pathway towards exclusive α-arylation via a cationic route. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.