A Cs 2 CO 3 -promoted domino reaction between thioaurones and sulfur ylides was developed. A series of spiro [benzo[b]thiophene-2(3H),1'-cyclopropan]-3-ones were obtained in good-to-high yields. The present domino strategy tolerated both electron-withdrawing and electron-donating groups on both thioaurones and sulfur ylides. The reaction mechanism and the origin of the observed diastereoselectivity were investigated.Scheme 4. The proposed mechanism and the stereoselectivity, along with the computed relative free-energy values (given in square brackets, kcal/mol) by DFT calculations.