Unsymmetrically 3,3'-substituted axially chiral bis(tetrahydroisoquinoline) N,N'-dioxides exhibit unique catalytic activity in the asymmetric allylation of aromatic aldehydes (up to 96% ee). The product of the enantioselective allylation of benzaldehyde served as abuilding block for the preparation of an intermediate in the synthesis of diospongine.