Abstract: A method includes preparing a protected amine compound represented by the following structural formula: wherein the dotted line - - - is a covalent bond or no bond. The method includes the step of, in the presence of superatmospheric CO2: a) intermolecularly reacting an iminium compound with a nucleophile Nu represented by the following structural diagram: or b) intramolecularly reacting an iminium group of an iminium compound represented by the following structural formula, the iminium compound having a nucleophile: with the nucleophile of the iminium compound, thereby forming the protected amine compound.