Suzuki Cross-Coupling Reactions: Synthesis of Unsymmetrical Biaryls in the Organic Laboratory

Abstract

An organic chemistry laboratory experiment in which unsymmetrical biaryl alcohols are synthesized in a two-step process is described. In the first step, an aryl boronic acid is coupled with p-bromoacetaldehyde or p-bromoacetophenone. The carbonyl group of the product is reduced with sodium borohydride in the second step. The products of both reactions are solids that can be easily purified by recrystallization. The primary purpose in implementing this experiment was to give students additional exposure to transition-metal-catalyzed reactions. The experiment provides an opportunity to discuss a number of topics, including the palladium-catalyzed cross-coupling mechanism, reactions that permit the formation of C-C bonds in an aqueous environment, the reduction of carbonyl groups with metal hydrides, and atropisomerism. The students can use IR and 1H NMR spectroscopy to determine the structure of their products, and so this laboratory also allows them to improve their spectral interpretation skills.