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.

本研究采用密度泛函理论计算方法，对芳基叠氮化物在铁(II)溴化物催化下的分子内C-H键胺化[1,2]-转移串联反应机制进行了探讨。计算了从R1，1-叠氮-2-(1-甲氧基-2-甲基丙烷-2-基)苯，到产物P2，2,3-二甲基-1H-吲哚的串联反应过程。我们的研究结果表明，整个催化循环包括以下步骤：（I）氮气从铁氮烯中挤出；（II）C-H键胺化；（III）中间产物P1，2-甲氧基-3,3-二甲基吲哚的形成；（IV）亚胺离子形成；（V）[1,2]-转移过程；（VI）吲哚P2的形成。速率决定步骤为[1,2]-转移过程，其中气相中的能量障碍ΔE = 28.7 kcal/mol。我们的计算结果还表明，串联反应中[1,2]-转移成分的优先顺序为甲基 < 乙基。