Fast and efficient nickel(II)-catalysed transfer hydrogenation of quinolines with ammonia borane

Abstract

Herein we report the first Ni(II)‐catalysed transfer hydrogenation of quinolines using ammonia borane (AB) as hydrogen (H2) source. An in situ generated Ni(II)‐bis(pyrazolyl)pyridine pre‐catalyst could hydrogenate quinoline and its derivatives in excellent yields of up to 90% at 25 °C in 30 minutes. Spectroscopic studies revealed that a Ni(II)‐hydride is responsible for the transfer hydrogenation of quinoline to 1,2,3,4‐tetrahydroquinoline via a 1,4‐dihydroquinoline intermediate