Density Functional Theory Study of the Mechanisms of Iron-Catalyzed Intramolecular C–H Amination [1,2]-Shift Tandem Reactions of Aryl Azides

The
mechanisms of iron­(II) bromide-catalyzed intramolecular C–H
bond amination [1,2]-shift tandem reactions of aryl azides have been
studied using density functional theory calculations. The tandem reaction
from R1, 1-azido-2-(1-methoxy-2-methylpropan-2-yl)­benzene,
to produce P2, 2,3-dimethyl-1H-indole, was calculated. Our results showed that the overall
catalytic cycle includes the following steps: (I) extrusion of N2 to form iron nitrene; (II) C–H bond amination; (III)
formation of the middle product P1, 2-methoxy-3,3-dimethylindoline; (IV) iminium ion formation ; (V)
[1,2]-shift process; and (VI) formation of indole P2. The rate-limiting step is the [1,2]-shift process,
where the energy barrier ΔE = 28.7 kcal/mol
in the gas phase. Our calculated results also indicated that the preference
for the [1,2]-shift component of the tandem reaction is methyl <
ethyl.