Spiro heterocyclization of dimethyl 1-(4-methylphenyl)-4,5-dioxo-4,5- dihydro-1H-pyrrole-2,3-dicarboxylate by the action of 3-arylamino-5,5- dimethylcyclohex-2-en-1-ones

Reactions of dialkyl 4,5-dioxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylates with enamines were reported previously. By reaction of 1-(4-methylphenyl)-4,5-dioxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylate (I) with an equimolar amount of 3-arylamino-5,5-dimethylcyclohex-2-en-1-one IIa or IIb in boiling toluene (reaction time 3–4 h) we obtained methyl 1-aryl-1′-(4methylphenyl)-4′-hydroxy-6,6-dimethyl-2,4,5′-trioxo1,1′,2,4,5,5′,6,7-octahydrospiro[indole-3,2′-pyrrole]-3′carboxylates IIIa and IIIb. The spectral parameters of compounds IIIa and IIIb turned out to be quite similar to those of model 3′-benzoyl-1-cyclohexyl-4′-hydroxy6,6-dimethyl-1′-phenyl-1,1′,2,4,5,5′,6,7-octahydrospiro[indole-3,2′-pyrrole]-2,4,5′-trione whose structure was proved by X-ray analysis [1].