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Fused pyrazole systems are biologically important molecules. An efficient two-step protocol has been developed to make new molecules of this family via the reaction between dimethyl acetylenedicarboxylate, triphenylphosphine and N-aminophthalimide in the presence of benzoic acid or N-aminophthalimide derivatives. This reaction occurred easily in an ambient temperature to give stable phosphorus ylides, which, upon heating, underwent an intramolecular Wittig reaction to afford the pyrazolo [5, 1-a] isoindole derivatives.