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

AbstractA 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.