1,7‐Electrocyclization Reactions of 2‐Aza‐4,5‐benzoheptatrienyl‐ and 4‐Aza‐6,7‐benzononatetraenyllithium Compounds: Synthesis of Novel 2‐Benzazepines and (Benzocyclooctenyl)amines

Abstract

Deprotonation reactions of N‐benzyl‐ and N‐allylimines 1 and 4 led to benzo‐annulated 2‐azaheptatrienyl‐ and 4‐azanonatetraenyllithium compounds, which underwent 1,7‐electrocyclization reactions to yield the novel 2,3‐dihydro‐1H‐benzo[c]azepines 3, 5, 11 and 13 or the (5,6‐dihydrobenzocycloocten‐5‐yl)amines 6 after subsequent addition of acyl chlorides, carbamoyl chlorides, imidoyl chlorides or pivaldehyde, respectively. Acyl and carbamoyl chlorides reacted as electrophiles at the nitrogen atom, whereas imidoyl halides and pivaldehyde attacked position C‐5 in the seven‐membered ring. In the case of pivaldehyde, the final tricyclic product 13 is the result of a subsequent nucleophilic attack at the imine moiety after a proton shift. The temperature dependence of the reaction cascades was studied, allowing preferred formation either of the seven‐membered heterocyclic systems 3 and 5 or of the eight‐membered carbocycles 6. All compounds were fully characterized, including by X‐ray diffraction studies of 6c, 6f, 11a and 13a. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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

“…Various applications of these principles allowed easy and straightforward access to a large number of N-heterocyclic systems just by appropriate positioning of the nitrogen atom in polyenylic anionic starting materials . Besides linear examples, also benzannulated compounds react in the same manner.…”

Recent advances in 8π electrocyclization reactions

“…33 Later, this method was further extended to aromatic imines substituted with alkynyl or alkenyl groups (Scheme 13). 34 These reactions successfully converted various carbo- and heterocyclic alkynylimines and alkenylimines into their corresponding azepines. In terms of the mechanism, the treatment of imines with a strong base formed a p–π conjugated eight-electron system that afforded azepine derivatives by means of an 8π electrocyclization reaction.…”

Modification and Unexpected Reactivity of 2-Borylbenzaldimines: Acylated and Silylated Derivatives as Well as Dimeric Compounds

“…Our group is well experienced in the preparation and application of anionic intermediates: e.g., by deprotonation of aza- and diazapolyenes for subsequent electrocyclic reactions − and for effective functionalization . Thus, we report herein the synthesis of novel N -alkyl and benzyl B/N heterocyclic compounds 3 with a CH 2 R group in the position α to nitrogen, allowing for deprotonation to give borylated 2-azaallyl- and 2-azapentadienyllithium compounds .…”