arenesulfonyl chlorides with cis- or trans-β-methylstyrene catalyzed by dichlorotris(triphenylphosphine)ruthenium(II) in the presence of triethylamine proceeded smoothly to give only (E)-2-arylsulfonyl-1-phenylpropene. The recovered cis-β-methylstyrene was isomerized to trans form, while trans-β-methylstyrene did not isomerize to the cis one.