ASYMMETRIC DIELS-ALDER REACTIONS OF CHIRAL (E)-2-CYANOCINNAMATES WITH CYCLOPENTADIENE

Several chiral derivatives of (E)-2-cyanocinnamic acid are used as trisubstituted dienophiles, and their asymmetric Diels-Alder reactions with cyclopentadiene are studied. The reactions of (E)-2-cyanocinnamates of (S)-ethyl lactate and (R)-pantolactone with cyclopentadiene, catalyzed by TiCl4, allow the synthesis of enantiomerically pure cycloadducts whose absolute configurations are assigned by an X-ray diffraction study of enantiomerically pure (1S,2S,3R,4R,5R,6R)-iodolactone. The results obtained show that the alpha-cyano group influences asymmetric induction, probably through an influence on the s-cis/s-trans equilibrium of the enoate moiety of the chiral dienophile.