N-heterocyclic carbene/copper-cocatalyzed
[4 + 3] annulation of
salicylaldehydes with aziridines was developed, giving the corresponding
1,4-benzoxazepinones in good yields with exclusive regioselectivity.
Copper serves as a Lewis acid to activate the small strained aziridines,
and the formation of NHC-salicylaldehyde adduct plays an important
role in improving the regioselectivity.