An Unexpected Reaction of 3-Ethoxycyclohex-2-enone with 3-Oxo-1,2-pyrazolidinium ylides: Preparation of 9-aryl-xanthenediones

An unexpected result from the reaction of 3-ethoxycyclohex-2-enone with 3-oxo-1,2-pyrazolidinium ylide is described. This transformation catalyzed by TFA/H2O in the presence of DMSO, leading to 9-aryl-xanthenediones in good yields (75-94%). The structures of the prepared compounds were characterized thoroughly by IR, elemental analysis, MS, NMR together with X-ray crystallographic analysis. A possible mechanism of this unusual reaction process is proposed.