Threo and erythro-δ-hydroxy-α,β-unsaturated γ-lactones are obtained with useful diastereoselection by condensing 2-trimethylsiloxyfuran and aldehydes by varying the reaction reaction conditions. A stereomechanistic rationale is presented together with a practical two-step synthesis of the threo and erythro 5-hydroxy-4-decanolides (L factors).