Three-component spiro heterocyclization of pyrrolediones with malononitrile and pyrazolone

The reaction of ethyl 1-benzyl-4,5-dioxo-2-phenyl4,5-dihydro-1H-pyrrole-3-carboxylate (Ia) and 4,5-diphenyl-1H-pyrrole-2,3-dione (Ib) with malononitrile and 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one at a ratio of 1 : 1 : 1 in boiling anhydrous toluene in the presence of an equimolar amount of triethylamine (reaction time 20–30; TLC monitoring) gave substituted 6-amino-3-methyl-2′-oxo-1,5′-diphenyl-5-cyano-1′,2′dihydro-1H-spiro[pyrano[2,3-c]pyrazole-4,3′-pyrroles] IIa and IIb. Compounds II are likely to be formed as a result of initial condensation of the ketone carbonyl group of pyrroledione I (C=O) with the activated methylene group of malononitrile, followed by nucleophilic addition of the CH carbon atom and OH group of the pyrazolone enol tautomer to C and cyano carbon atom, respectively. The described reaction is the first example of threecomponent spiro heterocyclization of substituted 1H-pyrrole-2,3-diones with malononitrile and fivemembered heterocyclic enol, leading to the formation of difficultly accessible spiro[pyrano[2,3-c]pyrazole4,3′-pyrrole] heterocyclic system. Ethyl 6-amino-1′-benzyl-5-cyano-3-methyl-2′oxo-1,5′-diphenyl-1′,2′-dihydro-1H-spiro[pyrano[2,3-c]pyrazole-4,3′-pyrrole]-4′-carboxylate (IIa). Malononitrile and triethylamine, 1 mmol each, were