The first synthesis of (-)-isoambreinolide, (+)-vitexifolin D and (+)-vitedoin B.

A very efficient method for synthesizing spirolactones is reported. Treatment of delta,epsilon-unsaturated carboxylic acids with iodine and triphenylphosphine under mild conditions leads to the corresponding spiro gamma-lactones in high yield and with complete stereoselectivity. Utilizing this, the first synthesis of the terpene spirolactones (-)-isoambreinotide, (+)-vitexifolin D and (+)-vitedoin B has been achieved.