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

AbstractDeprotonation 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)