2-(2-Hydroxyaryl)cinnamic amides: a new class of axially chiral molecules

The syntheses of several differently substituted amides formally derived from a chiral amine, either E-2-(2-hydroxyphenyl)cinnamic acid or both E- and Z-2-(2-hydroxynaphthyl)cinnamic acid, are reported. These molecules display a restricted rotation about the C2-Caryl bond. The barriers to rotation about the C2-Caryl bond were measured by the dynamic 1H NMR and were found to vary between 11.8 and 24.5 kcal mol-1, depending on the substitution. In particular, E-2-(2-hydroxynapthyl)cinnamic amides, displayed a high barrier to rotation (ΔGc‡ = 24.4 kcal mol-1) and could be isolated in both diastereomerically pure forms at room temperature. The X-ray structure of one E-2-(2-hydroxynapthyl)cinnamic amide, was resolved, enabling for the determination of the absolute configuration of the chiral axis (aR).