Stereoselective Synthesis of (+)-Annuionone A and (-)-Annuionone B.

A stereoselective synthetic approach was utilized to synthesize enantiopure annuionones A (1b) and B (2b), two ionone-type norsesquiterpenoids that both bear a 6-oxabicyclo[3.2.1]octane framework and possess allelopathic activity. A stereoselective Diels-Alder reaction based on chiral trisubstituted dienophile 20 was employed to obtain the optically active polysubstituted cyclohexane core of both natural products. Using this approach, (+)-annuionone A (1b) and (-)-annuionone B (2b) were synthesized from lactol (+)-15 in 10% overall yield.