Experimental Investigation of an Oxidative C−C Coupling Reaction Catalyzed by HAuCl₄

Abstract Reaction monitoring by electrospray (ESI) mass spectrometry (MS) is a valuable technique to investigate reaction mechanisms. It allows a glimpse into the reacting solution and the characterization of transient intermediates by tandem mass spectrometry. Herein we studied an intriguing gold(III)‐catalyzed synthesis of dicoumarins which includes a combination of hydroarylation and homocoupling steps. Reactants and products could be detected in positive mode. In negative mode, some species corroborating proposed transient intermediates could be detected by direct infusion ESI of reacting solutions. The ions were characterized by accurate mass determinations and gas‐phase fragmentation. Thus, indications for the nature and ligand sphere of reaction intermediates in the catalytic cycle could be collected.