The [2,3]-sigmatropic rearrangement of propargyl benzenesulphinates to allenyl phenyl sulphones

α-Methyl-, α-phenyl-, α,α -dimethyl-, and α-ethyl-α-methylpropargyl benzenesulphinates were found to undergo thermal rearrangement in high yields to sulphones, accompanied by a simultaneous acetylene-allene isomerization. The allenic sulphones produced by the rearrangement of the α-monosubstituted propargyl esters underwent further rearrangement under the reaction conditions, to γ-substituted propargyl phenyl sulphones, by way of a base-catalyzed [1,3] - prototropic shift. A kinetic study of the rearrangement reaction was carried out using two different esters. This study revealed that the rearrangement exhibited a relatively low sensitivity to the effect of solvent ionizing power and substituents. These data and other pertinent evidence suggest a concerted [2,3] - sigmatropic rearrangement.