Studies on the Reaction of Cycloalkanones with Malonodinitrile

Cyclopentanone reacts with malononitrile catalyzed by piperidine or sodium acetate to afford under any case cyclopentylidenemalononitrile dimer: 5‐aminospiro‐[2,6,7,7a‐tetrahydroindene‐7,1′‐cyclopentane]‐4,6,6‐tricarbonitrile ( 7 ) as the sole product. Contrary to this behavior, cyclohexanone reacts with malononitrile catalyzed by piperidine to afford the analogous cyclohexylidenemalononitrile dimer: 2‐aminospiro‐[3,4,5,6,7,4a‐hexahydronaphthalene‐4,1′‐cyclohexane]‐1,3,3‐tricarbonitrile ( 11 ); whereas when the reaction is catalyzed by sodium acetate, it afforded 9,10‐diaza‐8,11‐dioxo‐tricyclo‐[4.3.3.0^1,6]‐dodecane‐7,12‐dicarbonitrile ( 12 ). The structures of these products were established on the basis of their elemental analysis and spectral data, and plausible mechanism has been postulated to account for their formation. X‐ray crystallography was carried out as a further evidence for structures 7 and 12 .