Asymmetric Synthesis of C₂-Symmetric Vicinal Diamines via Reductive Dimerization of N-Acylpyridinium and Related Salts

A new route to C₂-symmetric diamines via an asymmetric reductive dimerization of 1-acylpyridinium salts and their benzo derivatives is described. This method is practical as the starting heterocycles and chiral auxiliaries are readily available. The titanium reducing agent is inexpensive and easy to prepare. Several novel enantiopure C₂-symmetric diamine derivatives were synthesized using this method.