An investigation of the chemistry of phenylsulphonylcyclopentadiene

Phenylsulphonylcyclopentadiene (7) exists mainly as the 1-isomer, and the assigned structure of its dimer (6) has been corroborated by n.m.r. decoupling experiments. Both the diene (7) and its cyclopentadienide anion (8) were unusually unreactive, although anion (8) rapidly perdeuteriates and undergoes Michael addition, α to the sulphonyl group, to methyl vinyl ketone, albeit in very low yield to form adduct (11). On being heated to 65 °C compound (11) rearranges, and two consecutive 1,5-shift products have been tentatively identified by n.m.r. spectroscopy.