Cycloaddition of C,C‐Disubstituted Ketonitrones with Acceptor Methylenecyclopropanes and Subsequent Rearrangement Cascade of 5‐Spirocyclopropane‐isoxazolidines

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 1 to the double bond of dimethyl methylenecyclopropane-1,2-dicarboxylate 2 or 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 4 or pyrrolo[1,2-a]quinolines 6.