Fast transimination in organic solvents in the absence of proton and metal catalysts. A key to imine metathesis catalyzed by primary amines under mild conditions

Abstract

Amine–imine exchange reactions of sterically unhindered reactants were found to be surprisingly fast at room temperature in a variety of nonaqueous solvents in the absence of proton and metal catalysts. The reaction mechanism suggested by ab initio calculations in the gas phase involves nucleophilic addition to the CN bond in concert with proton transfer from the amine NH bond to the imine nitrogen via a highly imbalanced transition state. These very fast transimination reactions were utilized in the catalysis of imine metathesis. Imine metathesis, usually carried out in organic solvents at high temperature in the presence of metal catalysts, occurs smoothly at room temperature in the presence of primary amines under nonacidic conditions as a result of coupled transimination processes. Kinetic data fully consistent with the proposed reaction mechanism were obtained.