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.