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. 1,3‐Dipolar cycloaddition of acceptor ring‐substituted methylenecyclopropanes and trisubstituted N,C,C‐triaryl‐ and N‐aryl‐C,C‐bis(methoxycarbonyl)nitrones proceed with the formation of new polycycliccompounds with azeto[1,2‐a]quinoline or pyrrolo[1,2‐a]quinoline cores.