Novel polycyclic heterocycles. XI. Synthesis of 11,12‐dihydropyrido[2,1‐b] [1,3]benzodiazepines, 6H‐pyrido[1,2‐c] [1,3,5]benzoxadiazepines, and 6H‐Pyrido[1,2‐c] [1,3,5]benzothiadiazepines

An unusually facile dehydrobromination, involving the ortho‐bromine atom and the = NH proton of a 2‐imino‐1‐(phenethyl)‐, 2‐imino‐1‐(phenoxymethyl)‐, or 2‐imino‐1‐(phenylthiomethyl)‐pyridine (2a‐e) has led to the synthesis of three novel bridgehead nitrogen tricyclic systems: 11,12‐dihydropyrido[2,1‐b] [1,3]benzodiazepines (3a,b), 6H‐pyrido[1,2‐c] [1,3,5]benzoxadiazepines (3c,d) and 6H‐pyrido[1,2‐c][1,3,5]benzothiadiazepines (3e). As anticipated, these cyclizations required a base, e.g., potassium carbonate, and a catalyst, e.g., copper bronze. What was unusual, was that these reactions occurred in methanol or n‐propanol, under reflux, either under anhydrous conditions, or in the presence of large amounts of water. The pmr spectra of these compounds are discussed.