Assembly of Pyrano[2,3- <i>c</i> ]pyrazol-5-ol from Electron-Deficient Bifunctional Peroxides via Michael Addition/Cyclization/Ring-Opening

A base-mediated formal [3+3] annulation between electron-deficient bifunctional peroxides and pyrazolones was disclosed, delivering various pyrano[2,3-<i>c</i>]pyrazol-5-ols in good yields. This cascade annulation method exhibits mild conditions and good substrate tolerance. Preliminary mechanistic studies and DFT calculations provide strong evidence supporting the Michael addition/cyclization/ring-opening process. In vitro cytotoxicity experiments reveal that this simple protocol establishes a useful framework for synthesizing potential candidate molecules of antitumor drugs.