Starting from 2-chloropyridine 1, a series of 1, 2-diazepin-3-ones 16 was prepared by a five- step synthesis. The key intermediates were the bicyclic oxadiazolium salts 10 which led, through a methoside ion induced ring opening, to the expected 2-methoxypyridinium ylides 11. The photoinduced ring enlargement of ylides 11 proved to be regiospecific and led to 3- methoxy-l, 2-diazepines, the immediate precursors of the final diazepinones 16.
![N-[(4'-methoxybenzoyl)imino]-2-methoxypyridinium ylide Structure](https://image.chemsrc.com/caspic/158/75267-78-6.png)
