Efficient co-catalyzed transfer hydrogenation of quinoxalines with NH3BH3

A Co(II)-catalyzed transfer hydrogenation of quinoxalines to 1,2,3,4-tetrahydroquinoxalines using ammonia borane (NH 3 BH 3 ) as a hydrogen donor has been developed. Using only 1 mol% of catalyst, the reaction proceeds rapidly under mild conditions. A total of 21 substrates, including derivatives bearing natural-product fragments, were reduced within 5–10 min in excellent yields. Control and deuterium-labeling experiments reveal that the reaction follows a single hydrogen transfer (SHT) pathway. This work provides an efficient and operationally simple protocol for the transfer hydrogenation of quinoxalines using NH₃BH₃ as a mild and convenient hydrogen source.