[Display omitted] An interesting product divergence in the reaction of trifluorodiazoethane with arylidene-1,3-indanediones is reported. The reaction conducted using 10 mol% of silver carbonate afforded trifluoromethylspiropyrazolines, while with excess of cesium fluoride in methanol, the cycloaddition was followed by nucleophilic ringopening of the spiropyrazoline to afford trifluoromethylated -ca
diazomethylphosphonate leading to the formation of two different types of products is reported. The reaction carried out in acetone in the presence of catalytic amount of cesium fluoride afforded spiropyrazoline phosphonates via 1,3-dipolar cycloaddition reaction, whereas the reaction in methanol yielded an interesting class of pyrazolylphthalides. This strategy provides an efficient alternative method