Aromatic amination/imination approach to chiral benzimidazoles.

The powerful Buchwald-Hartwig amination was utilized for the construction of the benzimidazole nucleus with the substituted nitrogen atom bearing a chiral substituent. A successive amination/imination was followed by an acid-catalyzed ring closure step to give the benzimidazole ring. The products were deprotonated and acylated at the C2 position and could be alkylated on nitrogen to give chiral benzimidazolium salts.