(i) Zn, aq. HCl, (ii) Br2; Multistep reaction;

1: (E)-3-iodo-1-phenylsulfonylprop-1-ene With n-butyllithium in tetrahydrofuran; hexane T=-78°C; 0.0833333 h; 2: isobutyraldehyde in tetrahydrofuran 1 h; Further stages.;