Transition-Metal-Free Oxidative Cross-Coupling of Triorganoindium Reagents with Tetrahydroisoquinolines

Triorganoindium reagents (R3In) react with tetrahydroisoquinolines (THIQs) in the presence of Ph3CBF4 as oxidant to afford 1-substituted THIQs. The reaction proceeds in good yields at rt using 50 mol % of R3In with a variety of organic groups. 1H NMR studies show the generation of an iminium ion intermediate supporting a two-step mechanism based on THIQ oxidation and R3In nucleophilic addition. This reaction was applied to the synthesis of the alkaloid Nuciferine in three steps.