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

Arynes have been found to undergo formal sigma-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-1H-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.