Bislactonization of unsaturated diacids using lead tetraacetate

The reaction of lead tetraacetate with unsaturated carboxylic acids (or salts) to from bislactones (γ or δ) can be controlled to produce efficiently $\text{cis}$ addition of two carboxylic oxygens to the double bond, in consonance with an initial plumbolactonization step followed by S_N2 displacement of lead.