Sonogashira Coupling Catalyzed by Palladium on Polymer Supports

Chemfiles Volume 5 Article 11

Supported palladium catalysts are widely used in the Suzuki, Heck, and Sonogashira cross-coupling reactions. The advantages to using supported catalysts in organic synthesis include reagent stability, suitability for automation, ease of workup, recyclability, and lower Pd contamination in the final product. Here, we describe the application of four commercially available polymer-supported palladium reagents as catalysts in the Sonogashira coupling.

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Typical Experimental Procedure

The palladium catalyst (0.01 mmol Pd) is charged into the reaction vessel. Diethylamine (6 mL), followed by 2-bromo-6-methylpyridine (1.0 g, 5.8 mmol), phenylacetylene (1.2 g, 11.8 mmol), and copper(I) iodide (2.8 mg, 0.0145 mmol) is added to the reaction vessel. The resulting mixture is stirred at 55–60 ºC for 18 h, cooled, and then filtered. The resin is washed with THF (2 × 3 mL), the THF filtrates combined and evaporated to yield a dark colored oil. The oil is dissolved in ether (30 mL), extracted twice with water (10 mL) and twice with brine (10 mL), dried with anhydrous sodium sulfate, filtered and evaporated to yield a dark colored oil. The crude oil thus obtained is purified by flash chromatography on silica gel using ethyl acetate: hexane (9:1). The purified product, 6-methyl-2-(phenylethynyl)pyridine, is isolated as a yellow oil. (See the table below for yields.)

Cat. No. Catalyst Name Coupling Yield
596930 Dichlorobis(triphenylphosphine)palladium(II), polymer-bound 92%
654167 Diacetobis(triphenylphosphine)palladium(II), polymer-bound 91%
646555 Bis[(diphosphanyl)methyl]laminepalladium(II) dichloride, polymer-bound 88%
654159 Bis[(diphenylphosphanyl)methyl]aminepalladium( II) diacetate, polymer-bound 80%

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