An Efficient Synthesis of γ-Methylene-γ-butyrolactone (α'-Angelicalactone). Application to the Synthesis of Deoxyobtusilactone and Deoxyisoobtusilactone

The mercury(II)-catalyzed cyclization of 4-pentynoic acid proceeds efficiently to give γ-methylene-γ-butyrolac-tone (α'-angelicalactone). The enolate of this lactone reacts with 11-dodecenal producing separable diastereomeric β-hydroxylactones. The corresponding methanesulfonate derivatives undergo partially selective elimination to afford deoxyobtusilactone and deoxyisoobtusilactone.