O-HYDROXYPHENONES AND O-METHOXYCROTONOPHENONES AS DIENOPHILES IN THE CONVENTIONAL AND ASYMMETRIC DIELS-ALDER REACTION

The o-hydroxy and o-methoxycrotonophenones are highly reactive dienoph iles in the Diels-Alder reaction with cyclopentadiene promoted by a ti tanium catalyst, showing chemical yields as high as 95% depending on t he solvent. This reaction does not take place without Lewis acid in si milar experimental conditions. Moreover, the use of the chiral titaniu m catalyst derived from ,2-hexaphenyl-4,5-bis(hydroxymethyl)-1,3-dioxo lane (4) allows the synthesis of the optically active cycloadducts in high diastereoselectivity although with moderate to low enantiomeric e xcesses.