The dilemma between acid and base catalysis in the synthesis of benzimidazole from o-phenylenediamine and carbon dioxide.

The tandem synthesis of benzimidazole and other azoles can be achived by the N-formylation of ortho-substituted anilines followed by a cyclization reaction. However, CO2-based N-formylations with hydrosilane reducing agents are base catalyzed whereas the cyclization reaction is acid catalyzed. The mismatch in catalytic conditions means that only one of the steps can be catalyzed in a single pot reaction.