A new reaction cascade to give tricyclic cores of 2,4‐dihydro‐1H‐azeto[1,2‐a]quinolines (benzocarbacephems) and pyrrolo[1,2‐a]quinolines starting from acyclic N‐aryl ketonitrones and acceptor ring substituted methylenecyclopropanes has been reported. This reaction includes 1,3‐dipolar cycloaddition of N‐aryl‐C,C‐diaryl or N‐aryl‐C,C‐bis(methoxycarbonyl) nitrones 1to the double bond of dimethyl methylenecyclopropane‐1,2‐dicarboxylate 2or benzylidenecyclopropane‐1,1‐dicarboxylate 3, followed by Brandi–Guarna rearrangement of the initially formed 5‐spirocyclopropane‐isoxazolidine cycloadducts to give 2,4‐dihydro‐1H‐azeto[1,2‐a]quinolines 4or pyrrolo[1,2‐a]quinolines 6.