Zhenhua Zhang and Haifeng Du*

The hydrogenation of 2,3-substituted quinoxalines belongs to one of the unsolved problems. Therefore, the development of highly stereoselective hydrogenations of 2,3-disubstituted quinoxalines with a good substrate scope, especially, the corresponding asymmetric reactions, is still a challenging subject. In this work, a wide range of 2,3-disubstituted quinoxalines has been successfully hydrogenated using borane catalysts to produce tetrahydroquinoxalines in 80-99% yields with excellent cis-selectivities. Significantly, the asymmetric reaction employing chiral borane catalysts generated by the in situ hydroboration of chiral dienes with HB(C₆F₅)₂ under mild conditions has also been achieved with up to 96% ee, which represents the first catalytic asymmetric system to furnish optically active cis-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines, and also an important progress for the metal-free hydrogenation.

This work has been published in Angew. Chem. Int. Ed. 2015, 54, 623-626.