Dehydrative Condensation of Dicarboxylic Acids with Aminoboronic Acids

Significance

An efficient bifunctional Brønsted base assisted aminoboronic acid catalyst (3) has been developed by the authors for the intramolecular dehydrative condensation of dicarboxylic ­acids. With 1 mol% of catalyst 3 and RCN (R = Et, n-Pr, n-Bu) as solvent, various aromatic and aliphatic dicarboxylic acids can be converted into the corresponding anhydrides in high yields (73-100%) under azeotropic reflux conditions. The reaction is suggested to proceed via the formation of monoacyl boronate intermediates. In the proposed activation models A and B, one free amino group would act as a Brønsted base, while the protonated one would act as a proton donor.