Zur Synthese von Derivaten des Pyrido[1,2‐a]azepins

On the Synthesis of Derivatives of Pyrido[1,2‐a]lazepine The conjugated pyridinium ylides of type 4 undergo 8π ‐electrocyclisation affording the heterobicyclic allenes 5 which, in the presence of H2O and H2O2, are subsequently transformed into the substituted pyrido[1,2‐a]‐azepinones 6, a novel heterocyclic system. The chemical behaviour of 6a,b is dominated by cleavage of the lactam bond and subsequent reaction to pyridinc and isoquinoline derivatives, respectively; e.g. reaction of 6a, b with 4,5‐dihydro‐4‐methyl‐3H‐1,2,4‐triazole‐3,5‐dione affords the cycloadducts 11 and 12 almost quantitatively. The successful transformation of 6b into 15 is described, the latter being the first representative of the presently unknown, potentially antiaromatic pyrido[1,2‐a]azepine (1).