Science of Synthesis

Griesbeck, A. G.; Soldevilla, A., Science of Synthesis, (2008) 43, 368.

Iodoarenes are most commonly used for Sonogashira-like coupling reactions. For practical purposes, less reactive bromo- and chloroarenes are attractive as they are less expensive and more widely available than iodoarenes. One way of activating bromo- and chloroarenes for use in Sonogashira-type coupling reactions is to use a halogen-exchange (halex) reaction. This reaction can be followed by a palladium-catalyzed coupling, providing a one-pot procedure for the overall coupling between a bromoarene (or chloroarene) and a terminal alkyne (‌Scheme 29‌).[‌92‌] This so-called “domino” coupling is performed under very simple conditions; palladium supported on charcoal is used as the catalyst, and the reaction, in the presence of a base and with potassium iodide as iodide source, constitutes a copper- and ligand-free alternative to the standard Sonogashira protocols. The catalyst can be recovered and reused several times. However, despite its simplicity, the yields of ‌55‌ obtained with this protocol are only moderate to good (typically 30–60%).

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References