The first catalytic method for Heck alkynylation of unactivated aryl bromides (copper-free Sonogashira) in an ionic liquid: 1 mol-% palladium/triphenylphosphane/pyrrolidine in [BMIM][BF4] as a simple, inexpensive and recyclable system

摘要

Herein we report the studies of Heck alkynylation (copper-free Sonogashira) with aryl halides (I, Br, Cl) employing various metallic precursors, tertiary phosphanes and bases in [BMIM](BF4] as the solvent. As a result, we provide the first method that allows the coupling of a large array of substrates, either activated or deactivated bromides in an ionic liquid. Furthermore, the system of highest efficiency is unexpectedly the simplest and cheaper combination that employs [Pd(eta(3)-C3H5)Cl](2)/PPh3 at only a 1 mol-% loading with pyrrolidine as the base and in the absence of a copper salt. The coupling of sterically and electronically deactivated bromides bearing different functional groups to aryl- and alkyl acetylenes, as well as the possibility of recycling, make these results of high interest to the future development of Heck-and Sonogashira-type reactions in ionic liquids. (C) Wiley-VCH Verlag GmbH & Co.