Solvent-free synthesis of a series of differently N-substituted 4-amino-2-methylquinazolines under microwave irradiation

A fast, highly efficient and environmentally friendly microwave accelerated solvent-free procedure for the synthesis of a series of differently N-substituted 4-amino-2-methylquinazolines is developed. The transformation proceeded very clean, without any traces of side products. It was shown that aliphatic amines react quantitatively after 5 min irradiation, while the rate of conversion by anilines strongly depends on the place and the type of the substituents in their molecules. The results are explained by the competition of the steric and electronic effects of the amine substituents. The by-product of the reaction, hydrogen chloride, is quantitatively quenched as ammonium salts by the amines, used as nucleophiles, thus preventing its release into the environment.