Esterification Catalysis by Pyridinium p-Toluenesulfonate Revisited—Modification with a Lipid Chain for Improved Activities and Selectivities

The lipid analogues of pyridinium p-toluenesulfonate (PPTS) were examined for catalyzing the condensation of an equimolar mixture of carboxylic acids and alcohols under mild conditions without removal of water. Although PPTS is a poor catalyst, the introduction of a lipid chain and nitro group significantly improved the activity of PPTS and led to selectivity at suppressing elimination side reactions of alcohols. 2-Oleamido-5-nitro-pyridinium p-toluenesulfonate (6) is a lead catalyst that promoted various esterification reactions with yields up to 99%.