Ring Closure Reactions of 2,6-Diazaheptatrienyl Metal Compounds: Synthesis of 3-Aminoindole Derivatives and 14-Membered Macrocyclic Dimers

2,6-Diazaheptatrienyl metal compounds 6–K+ are
easily accessible from the corresponding diimines 6 by
deprotonation using KO-t-Bu as base. According to
quantum chemical calculations, they are, in comparison to other isomeric
species with nitrogen atoms in other positions, highly reactive intermediates,
which undergo in dilute solution at 50 °C ring closure reactions
to form 3-aminoindole derivatives 8/10. In contrast,
in more concentrated solution at room temperature, the formation of
14-membered macrocyclces 13 as a result of formal dimerization
is observed. The 3-aminoindole derivatives obtained in this work possess
rare substitution patterns, and the macrocyclic compounds are essentially
unknown. Two-fold vinylogous derivatives 7 give rise
to tricyclic systems with δ-carboline backbone 12. The experimental results are interpreted using high-level DFT calculations
with regard to the possible reaction mechanism and the nature of the
transition state of the five-membered ring formation. The molecular
structures in the solid state of all types of compounds were elucidated
by X-ray diffraction.

2,6-二氮杂庚三烯基金属配合物6–K⁺可通过以叔丁醇钾（KO-t-Bu）为碱，对相应的二亚胺6进行脱质子反应便捷合成。据量子化学计算结果，相较于其他氮原子位于不同位点的异构体，该类配合物属于高活性反应中间体：在50℃的稀溶液中，它们会发生环合反应，生成3-氨基吲哚衍生物8/10。与之相反，在室温下的浓溶液中，可观测到通过形式上的二聚反应生成14元大环化合物13的过程。本研究中获得的3-氨基吲哚衍生物具有罕见的取代模式，而这类大环化合物此前鲜有报道。双插烯衍生物7可形成带有δ-咔啉（δ-carboline）骨架的三环体系12。研究通过高精度密度泛函理论（DFT）计算对实验结果进行了解析，以探究其可能的反应机理及五元环形成过程的过渡态本质。所有类型化合物的固态分子结构均通过X射线衍射（X-ray diffraction）得以阐明。