Enantioselective N-heterocyclic carbene-catalyzed rearrangement of enol ε-lactones†

β-Lactones are common substructures in bioactive molecules. Herein, we developed an enantioselective N-heterocyclic carbene (NHC)-catalyzed rearrangement of enol ε-lactones for the construction of bicyclic β-lactones. The reaction works well for both exo- and endo-enol ε-lactones, giving the corresponding bicyclic β-lactones with two or three contiguous stereocenters, respectively. The reaction features readily available starting materials, 100% atom economy, mild conditions, high diastereo- and enantioselectivity.