Useful Ammonium Triflate Catalysts for Esterification

　DPAT (1) is a useful esterification catalyst developed by Tanabe et al. affording esters in high yields from equimolar amounts of carboxylic acids and alcohols under mild reaction condition.^1a-c) In this case, desired esters can be obtained by simple operation without addition of dehydrating agent and azeotropic water removal. There is also a report using fluorous solvent, in which 1 is useful for the substrate with high steric hindrance.^1d)
　PFPAT (2) shows higher activity than 1 and it can be applied widely to esterification and lactonization.^1b,c) Furthermore, 2 can be removed after work-up; washing with NaOH aqueous solution removed CF₃SO₃H, followed by distillation (C₆F₅NH₂: bp 153℃ / 760 mmHg). 2 is expected to be applied to various fields because it has high activity and it can be removed easily after the reaction.