Dehydrative Intramolecular Condensation Catalyst for the Synthesis of Carboxylic Anhydrides

2,6-Bis[(2,2,6,6-tetramethyl-1-piperidinyl)methyl]phenylboronic Acid (1) is a hybrid catalyst developed by Ishihara et al., which has Lewis acid and Brønsted base moieties in a molecule. A small amount of 1 smoothly catalyzes the dehydrative intramolecular condensation of dicarboxylic acids, such as phthalic acid, to afford the corresponding carboxylic anhydrides in high yields under mild conditions. In addition, it has been also reported that a diimide can be directly synthesized from a tetracarboxylic acid and a primary amine as a model reaction for the synthesis of polyimides.