2,2′-Biphenol-Derived Phosphoric Acid Catalyst for the Dehydrative Esterification of Carboxylic Acids with Alcohols

Abstract A dehydrative esterification from an equimolar mixture of carboxylic acids and primary or secondary alcohols in toluene at 100 °C was promoted without the necessity to remove water by using a simple 2,2′-biphenol-derived phosphoric acid catalyst (2.5–10 mol%). This reaction was also successfully conducted at the gram scale. To demonstrate the synthetic utility of this catalytic system, pharmaceutically useful substrates and acid-sensitive substrates were examined using these acid–base cooperative phosphoric acid catalysts, which exhibit relatively weak Brønsted acidity.