Sulfone

A sulfone contains an $\mathrm{R}-\mathrm{S}(\mathrm{O}{)}_2-R\prime$ group. An aryl sulfone withdraws electron density and commonly directs electrophilic aromatic substitution to meta positions.

$\mathrm{C}{\mathrm{H}}_2=\mathrm{CHS}{\mathrm{O}}_2\mathrm{Ph}$, an activated dienophile whose sulfone group can be removed reductively after cycloaddition.