Irradiation of N-methyl-1,2-naphthalendicarboximide 1 together with phenylacetylene in benzene afforded unprecedented reductive insertion products dihydronaphthazepinediones 2a and 2b, which were characterised by NMR spectroscopy (1H, 13C), IR spectroscopy, MS, elemental analysis and assignments confirmed by X-ray crystallographic analysis.