Microwave-Assisted Synthesis of 5-Phenyl-2-hydroxyacetophenone Derivatives by a Green Suzuki Coupling Reaction

In recent years, the use of boron-containing reagents in palladium-assisted C-C coupling reactions (the Suzuki reaction) has gained prominence due to the vast array of reagents commercially available. Consequently, the generation of carbon carbon bonds, namely of functionalized biphenyl systems, is at present considered the backbone of organic synthesis. In this context, the design of eco-friendly protocols for the Suzuki reaction employing water as a solvent and the use of microwave-assisted procedures are imperative from an industrial point of view. The series of laboratory experiences described highlight the skillfulness of microwave-assisted synthesis to promote environmentally friendly Suzuki reactions. In the first laboratory class, 1(4-hydroxy-4'-methoxy-[1,1'-biphenyl]-3-yl)ethanone and 1-(4'-chloro-4-hydroxy-[1,1'-biphenyl]-3-yl)ethanone are synthesized, and the crude products are obtained and purified. Students become acquainted with microwave equipment and several laboratory techniques, such as extraction, purification by filtration with celite, column chromatography, and thin-layer chromatography. In the second laboratory class, students check the purity of the compounds and acquire H-1 and C-13 NMR spectral data. The synthesized phenylacetophenone derivatives are key intermediates for the synthesis of many biological active molecules, namely, flavonoids, chromones, or coumarins, which are privileged structures for drug discovery. The experiments can be also performed with diverse arylboronic acids containing different electron donating and withdrawing groups, allowing the synthesis of a small library of benzopyran precursors. The experiments have been tested for three years by 75 graduate students in applied organic chemistry or medicinal chemistry curriculum units.