Spiro heterocyclization of methyl 4,5-dioxo-4,5-dihydro-1H-pyrrole-2- carboxylates with acyclic enamino ketones

Reactions of monocyclic 2,3-dihydro-1H-pyrrole2,3-diones with acyclic enamino ketones were not studied previously. We examined reactions of methyl 1-aryl-3-benzoyl-4,5-dioxo-4,5-dihydro-1H-pyrrole-2carboxylates Ia and Ib [1] with equimolar amounts of 4-arylaminopent-3-en-2-ones IIa and IIb and 3-(4-tolylamino)-1,3-diphenylprop-2-en-1-one (IIc). The reactants were heated in boiling anhydrous benzene or m-xylene for 2–240 min (until the reaction mixture turned colorless), and the products were the corresponding 9-acetyl-1,7-diaryl-4-benzoyl-3-hydroxy-8-methyl-1,7-diazaspiro[4.4]nona-3,8-diene-2,6diones IIIa and IIIb and 9-acetyl-1,7-diaryl-4-benzoyl-3-hydroxy-8-phenyl-1,7-diazaspiro[4.4]nona-3,8diene-2,6-diones IIIc and IIId. The spectral parameters of spiro compounds IIIa–IIId were very similar to those of model octahydrospiro[indole-3,2'-pyrroles] whose structure was proved by X-ray analysis [2, 3].