Asymmetric Synthesis of <i>C</i>₂-Symmetric Vicinal Diamines via Reductive Dimerization of <i>N-</i>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.