Double Hydroboration of Quinolines via Borane Catalysis: Diastereoselective One Pot Synthesis of 3-Hydroxytetrahydroquinolines

Described herein is an organoborane-catalysed consecutive borylative reduction of quinolines and isoquinolines to furnish tetrahydro(iso)quinolines bearing a C(sp(3))-B bond beta to the nitrogen atom. The installed C-B bond is oxidatively transformed to the hydroxy group in one pot. The present double hydroboration is proposed to proceed via a stepwise ionic mechanism involving a boronium ion. The stereo-outcome was found to be dependent on the position (C2 vs C4) of the substituents in quinolines.