Hydrogen-Bonding Catalysts are Hard to Predict

Significance

The authors synthesized various primary amine catalysts with fused hydrogenbonding donor moieties, among them 1-4, to study the influence of the pK _a of the donor moiety, thus the hydrogen bonding ability in detail. The studied conjugate additions gave ambivalent results. However, it became clear that catalysts with either very acidic single hydrogen-bonding sites (1) or effective double hydrogen-bonding sites (3) are superior, since catalysts with less acidic (2) or without hydrogen-bonding abilities (4) were in most cases not comparably effective.