Various differently substituted (2‐alkenylbenzylidene)amines 4b−d gave, upon deprotonation with amide bases and addition of an electrophile, the respective 4,5‐dihydro‐3H‐benzo[c]azepines 6a−k in moderate to good yields. The imines 4 are easily accessible from 2‐bromobenzaldehyde (1) by Wittig olefination, formylation with DMF, and subsequent condensation with benzylamine. The ring‐closure reaction is interpreted as an anionic 1,7‐electrocyclization reaction involving benzo‐annulated 2‐azaheptatrienyllithium compounds. This reaction, and the subsequent addition of the electrophiles, proceed with excellent diastereoselectivity, determined by the (E) or (Z) configuration of the imines 4b−d. The corresponding allylimines 4e,f do not give ninemembered heterocycles 7, but rather the corresponding 3‐vinyl‐4,5‐dihydro‐3H‐benzo[c]azepines 6l,m. Molecular structures of several compounds 6 in the solid state were determined by X‐ray crystallography, including the structure of a 14‐membered ring dimer 8. High‐level quantum chemical calculations on model anions concerning structures and relative energies of possible intermediates and transition states support the pericyclic mechanism suggested for the ring‐closure reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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.

No abstract

Ring Closure Reactions of 2,6-Diazaheptatrienyl Metal Compounds: Synthesis of 3-Aminoindole Derivatives and 14-Membered Macrocyclic Dimers. -In dilute solution, potassium salts of diimines of type (I) undergo intramolecular cyclization to afford 3-aminoindoles. In more concentrated solution they undergo dimerization to 14-membered N-heterocycles. The vinylogous analogue (IX) provides the δ-carboline (X) under dilute conditions. -(NEUE, B.; REIERMANN, R.; GERDES, K.; FROEHLICH, R.; WIBBELING, B.; WUERTHWEIN*, E.-U.; J. Org. Chem. 76 (2011) 21, 8794-8806, http://dx.

No abstract