Abstract
The asymmetric hydrogenation of N-heteroarenes provides an efficient
method for the synthesis of optically active cyclic secondary amines. In
this paper, we described an asymmetric hydrogenation of phenanthridines
using a chiral mono-alkene-derived borane. A variety of
dihydrophenanthridines were furnished in high yields with up to 93% ee.
The current catalytic system was very sensitive for the steric hindrance
of phenanthridines. Bulky substituents at one phenyl group of
phenanthridines were required to obtain the high enantioselectivity. But
large substituents adjacent to the C=N bonds would diminish the
reactivity sharply.