Mechanistic and selectivity investigations into Fe-catalyzed 2, 3-disubstituted azaindole formation from β,β-disubstituted tetrazole

Computational studies at the B3LYP-D3(BJ) level were performed to explore the mechanism and migratorial selectivity of Fe-catalyzed 2,3-disubstituted azaindole formation from beta, beta-disubstituted tetrazole and mecha-nistic details of key steps in this reaction are compared to those in Rh2-catalyzed indole formation. The calculated results show: Fe-catalyzed spirocyclization proceeds via a radical pathway, which is contrary to Rh-2-catalyzed spirocyclization that occurs via a carbocation pathway; the migration of C -> C significantly prefers to that of C -> N due to far lower breakage extents of Fe-N and C-C bonds. In addition, the comparisons of uncatalyzed vs. catalyzed N-2 extrusion and C -> C migration show that iron porphyrin catalyst can lower activation energies of these two steps.