Construction of Sulfonyl Oxabenzo[3.3.1]bicyclic Core via Cyclocondensation of β‑Ketosulfones and o‑Formyl Allylbenzenes

NH4OAc mediated domino Knoevenagel/Diels–Alder cyclocondensation of β-ketosulfones 1 and o-formyl allylbenzenes 2 provides sulfonyl oxabenzo[3.3.1]­bicyclic core 4 in a cosolvent of toluene and HOAc (v/v = 1/1) at reflux for 3 h. The intermediate 3 contains a chalcone motif. The uses of various ammonium salts and solvent systems are investigated for facile and efficient transformation. The plausible mechanisms have been proposed and the DFT calculations have been included.