The β-lactone route to α,β-unsaturated δ-lactones. Total syntheses of (±)-goniothalamin and (−)-massoialactone

The HF-induced translactonization of 2′-silyloxy-3-trimethylsilyl-2-oxetanones, obtained through Lewis acid-promoted [2+2] cycloaddition between β-silyloxyaldehydes and trimethylsilylsilylketene, into α,β-unsaturated δ-lactones is applied to the syntheses of (±)-goniothalamin and (−)-massoialactone.