Sonogashira Coupling Reaction of Aryl Derivatives: A Versatile Method for Acetylide Building Blocks

Abstract

The coupling of aryl or vinyl halides with terminal acetylenes catalysed by palladium, commonly known as the Sonogashira cross-coupling reaction, is one of the most important and widely used sp 2 –sp carbon–carbon bond formation reactions in organic synthesis. The obtained prod- ucts have frequently found applicability in several areas of chemistry, such as natural products, biologically active molecules, dyes, molecular electronics, dendrimers and conjugated polymers. The objective of this work is to obtain trimethyl[(5-nitrothiophen-2-yl)ethynyl]silane as an example of Sonogashira coupling reaction between a terminal alkyne (ethynyl(trimethyl)silane) and an aryl compound (2-bromo-5-nitrothiophene) in a first step. The protected alkyne is then deprotected by the use of ammonium fluoride to afford 2-ethynyl-5-nitrothiophene in excellent yield. This experiment constitutes a good introduction to basic organometallic reactions involved in Pd catalysed organic synthesis, namely oxidative addition, reductive elimination and transmetalation, as well as to the use of dry solvents and inert atmosphere conditions.