Quaternary Ammonium, Phosphonium, and Tertiary Sulfonium Salts as Hydrogen‐Bonding Catalysts

The powerful synthetic utility of onium salts such as quaternary ammonium, phosphonium, and tertiary sulfonium salts is well established in the field of organic chemistry. Quaternary ammonium and phosphonium salts are known as reliable organocatalysts in ion-pairing catalysis via the activation of anionic nucleophiles. Although ion-pairing catalysis is a major direction for onium salt catalysis, hydrogen-bonding catalysis of onium salts, which is promoted via the activation of electrophiles, has received attention in recent years. This chapter introduces new possibilities of onium salt catalysts as hydrogen-bonding catalysts.