A convenient Michael addition/cyclization sequence of alkyl isocyanide–acetylenic ester zwitterionic adducts with various pyrazolone derivatives, leading to the formation of dialkyl 6-(alkylamino)-1-methyl-4-oxo-3-phenyl-9-aryl-2,3-diazaspiro[4.4]nona-1,6,8-triene-7,8-dicarboxylates in moderate to good yields, is described. The structure of the target compounds was confirmed by an X-ray diffraction study.
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