Synthesis and application of axially chiral biscarbolines with functional N-O and sulfone for 1,2-transfer hydrogenations of ketimines

A series of axially chiral biscarboline-based sulfones were synthesized from l-tryptophane and applied for enantioselective 1,2-transfer hydrogenations of ketimines using trichlorosilane. The catalyst 4e, which had a tertiary butyl group, exhibited a good conversion and high enantioselectivities up to 96%ee in the series of reactions.