Theoretical studies on iron-catalyzed azaindoline formation: mechanism and site-selectivity.

The mechanism and site-selectivity for Fe-catalyzed azaindoline formation from 1,2,3,4-tetrazole were examined computationally. The H-atom abstraction/radical rebound stepwise mechanism is proposed. The aliphatic H-atom abstraction (HAA) vs. electrophilic aromatic substitution (EAS) steps are responsible for the sp3vs. sp2 C–H amination site-selectivity and a larger steric congestion disfavors sp2 EAS, thus resulting in Fe-catalyzed site-selectivity toward sp3 C–H amination.