A consecutive synthesis of spiro[cyclopenta[b]pyrrole-5,2'-indene] derivatives via spirocyclization/annulation...

The reaction between ninhydrin-malononitrile adduct [2-(1,3-dioxo-1,3-dihydro-2H-inden-2-ylidene)malononitrile] and ethyl 2-(alkylamino)-4-aryl-4-oxo-but-2-enoates (prepared from ethyl 2,4-dioxo-4-arylbutanoate and alkylamines) in the presence of Et₃N in MeCN at room temperature afforded 3-alkylamino-2-aryloyl-1',3',4-trioxo-1',3'-dihydrospiro[cyclopentane-1,2'-inden]-2-ene-5,5-dicarbonitriles in 78-95% yields. Five derivatives of these NH-acidic compounds are used to intercept the reactive zwitterionic intermediates generated from dimethyl acetylenedicarboxylate and Ph₃P to produce dimethyl 4,4-dicyano-6-aryloyl-1-alkyl-1',3'-dioxo-1',2,3',4-tetrahydro-1H-spiro[cyclopenta[b]pyrrole-5,2'-indene]-2,3-dicarboxylates. Radical scavenging activity of four derivatives was investigated by radical trapping of diphenylpicrylhydrazine and ferric reduction power experiments. The antibacterial activities of six derivatives were studied by disk diffusion test on Gram-positive and Gram-negative bacteria.