Investigations of the Copper‐Catalyzed Oxidative Cross‐Coupling of Tetrahydroisoquinolines with Diethylzinc by a Combination of Mass Spectrometric and Electrochemical Methods

Abstract The aerobic oxidative cross‐coupling of tetrahydroisoquinolines (THIQs) with diethylzinc catalyzed by CuCl 2 has been examined by means of electrospray mass spectrometry (ESI‐MS). Substrates, intermediates, and the product were readily detected. Particular emphasis has been placed on the role of CuCl 2 . Formation of the intermediate iminium species has been investigated in more detail by ESI‐MS, electrochemistry‐coupled ESI mass spectrometry (EC‐MS), and cyclic voltammetry (CV). Our experiments have consistently revealed strong influences of the N‐substituent of the THIQ derivative and its oxidation stability with respect to CuCl 2 . The results may help to expand the synthetic scope of the reaction, while also further establishing EC‐MS as a valuable technique for linking mass spectrometry with cyclic voltammetry in mechanistic studies of organic redox reactions.