Enantioselective Baeyer-Villiger Oxidation of 3-Substituted Cyclobutanones

Significance

The authors report an organocatalytic Baeyer-Villiger reaction of 3-substituted cyclo­butanones 1, leading to enantiomerically enriched γ-lactones 2. The reaction is catalyzed by chiral phosphoric acids and 30% aqueous H₂O₂ is used as oxidant. The highest enantioselectivities were achieved in chloroform at -40 °C with catalyst 3. Thus, a variety of 3-aryl-substituted cyclo­butanones was converted into the corresponding lactones in excellent yields (91-99%) and moderate to high enantioselectivities (er = 78:22 to 97:3). In one case the catalyst loading could even be reduced to 1 mol% without loss of enantio­selectivity.