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

Triorganoindium reagents (R3In) react with tetrahydroisoquinolines (THIQs) in the presence of Ph3CBF4 as an oxidant to afford 1-substituted THIQs. The reaction proceeds in good yields at rt using 50 mol % 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.