New synthetic methodology for ring expansion of n-sized conjugated cycloalkenones into homoallylic n+3 lactones: 3-step synthesis of fragrant phoracantholide

Under the influence of Lewis acidic boron trifluoride–diethyl etherate, epoxides are activated sufficiently to undergo rapid nucleophilic opening by ketone enolate ions at −78°C, forming useful γ-lactols. Application of this protocol to n+3 ring expansion features one-flask, multicomponent, sequential reactions.