Planar Chiral PHANOLs as Organocatalystsfor the Diels-Alder Reaction via Double Hydrogen-Bondingto a Carbonyl Group

Planar chiral PHANOLs have been shown to catalyze Diels-Alder reactions of a,b-unsaturated aldehydes and ketones with various dienes. Rate accelerations of up to ca. 30-fold were obtained using the electron deficient 4,12-dihydroxy-7,15-dinitro[2.2]paracyclophane as a catalyst. It is proposed that the carbonyl group of the dienophile is activated via a double hydrogen-bonding mode. Although the PHANOLs are inherently chiral, little or no asymmetric induction was observed when using enantiopure (R)-PHANOL.