Planar Chiral PHANOLs as Double Hydrogen Bonding Donor Organocatalysts: Synthesis and Catalysis

Abstract 4,12‐Dihydroxy[2.2]paracyclophanediol (PHANOL; 1), and its para‐substituted derivatives 2, 5 and 7, were found to catalyse Diels–Alder cycloadditions of α,β‐unsaturated aldehydes or ketones with dienes and/or epoxide ring opening reactions with amines. The mode of catalysis by the PHANOLs is via double hydrogen bonding to the two sp2 lone pairs of a carbonyl group or the two lone pairs of the epoxide. The order of activity of the PHANOLs for catalysis of the Diels–Alder reaction essentially correlates with the expected hydrogen‐bond donor strength based on the degree of electron‐withdrawing capability of the group(s) in the para position. In contrast, ortho‐substituted PHANOLs 10, 11 and 14 were not active as catalysts due to steric interference with the double hydrogen bonding mode. 1H NMR and IR spectral data for the various PHANOLs are discussed in support of the proposed double hydrogen bond mode.