Enhanced Enantioselectivity in the Fluorescent Recognition of a Chiral Diamine by Using a Bisbinaphthyl Dialdehyde

A bisbinaphthyl dialdehyde shows greatly enhanced enantioselective fluorescent response (ef = 10.0) in the fluorescent recognition of a chiral diamine, 1,2-diphenylethylenediamine, over a previously reported monobinaphthyl dialdehyde (ef = 1.1). This compound can be used to determine the enantiomeric composition of the diamine by fluorescence measurement. The NMR and mass spectroscopic studies have demonstrated that the chirality matched reaction of the bisbinaphthyl dialdehyde with the diamine in the presence of Zn(OAc)₂ favors the formation of a macrocyclic product more than the chirality mismatched. This enantioselective cyclocondensation should contribute to the observed highly enantioselective fluorescent response because the macrocyclic Zn(II) complex is proposed to give much greater fluorescence enhancement than the acyclic ones.