Synthesis of both enantiomers of annuionone A (1), an allelopathic agent isolated from Helianthus annuus (sunflower), was accomplished. The absolute configuration of the naturally occurring I was determined to be IS,5R,8R. (c) 2005 Elsevier Ltd. All rights reserved.
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