A Ring Expansion Route to Benzofused N‐Heterocycles Through Aryne Insertion into 1,3‐Diaza‐heterocycles

Arynes have been found to undergo formal σ‐bond insertion into a C(sp3)–N bond for the first time. This transformation is utilized in the ring expansion of 1,3‐diaza‐heterocycles to afford benzofused medium‐ring N‐heterocycles in a single step. This represents a novel route to biologically relevant 2,3,4,5‐tetrahydro‐1 H ‐benzo[ e ][1,4]diazepines, prepared directly from easily accessible imidazolidines. An example of the ring expansion of a 1,3‐diazetidine is also reported, which affords the corresponding 1,2,3,4‐tetrahydroquinazoline.